Insect Pests of Wheat in North India: A Comprehensive Review of Their Bio-Ecology and Integrated Management Strategies

Abstract

Wheat (Triticum aestivum L.) is a vital food crop for majority of the world’s population. However, its yield potential is significantly threatened by insect pests, which adversely affect production, quality, and overall food security. The diverse array of insect pests throughout wheat’s growth stages necessitates a comprehensive understanding of their interactions with wheat cultivation. This review critically assesses the diversity, biology, ecology, and management strategies of major insect pests in North India, including aphids, termites, pink stem borer, gram pod borer, armyworm, and brown wheat mite. These pests infest wheat at various growth stages, posing significant challenges to sustainable production. Moreover, existing pest control strategies are challenged by evolving agronomic practices in the region and climate change globally. As agricultural systems worldwide aim for sustainability and resilience in the face of climate change, this review advocates for the adoption of an integrated pest management (IPM) approach combining innovative and traditional pest control strategies to enhance ecosystem services and fortify the resilience of agricultural systems. By interlinking these pivotal elements, this review presents a valuable perspective on the important pests affecting wheat and the currently used IPM practices, emphasizing the need for adaptive management in the context of evolving climate challenges.

1. Introduction

Wheat (Triticum aestivum L.), an esteemed member of the grass family Poaceae, is a vital staple food crop for majority of the world’s population [1]. Globally, 798.98 million tons of wheat were harvested in 2023 from approximately 220.4 million hectares (Mha) of land, making wheat the top-ranked grain crop by cultivated area during 2023 [2]. This cereal crop contributes about 20% of the total dietary calories and proteins worldwide [3,4]. Wheat is cultivated across a wide range of latitudes, with China, India, U.S.A., Russia, France, Canada, Australia, Germany, Pakistan, and Ukraine being the top ten wheat-producing countries [2]. However, wheat productivity is primarily constrained by a plethora of biotic and abiotic stressors [5]. Among biotic stressors, insect pests and diseases are the main limiting factors for wheat production, causing significant quantitative and qualitative losses [6]. Of the 10,000 documented insect species that damage crops used by humans for food [7], about 100 are harmful to wheat [8].

In India, wheat is the second most important cereal crop after rice and serves as a staple food, particularly in Northern India [9]. The country is the second-largest consumer of wheat globally, after China. Wheat is produced in many regions of India, including Uttar Pradesh, Punjab, Haryana, Madhya Pradesh, Rajasthan, Bihar, Maharashtra, Gujarat, Karnataka, West Bengal, Uttarakhand, Himachal Pradesh, and Jammu and Kashmir. However, the northern states like Uttar Pradesh, Punjab, Haryana, and Rajasthan, together account for about 65% of the country’s total wheat production. Uttar Pradesh ranks first in wheat production, contributing approximately 35.34 million metric tons in 2024, followed by Punjab with 17.74 million metric tons and Haryana with 11.19 million metric tons [10].

In India, insect pests cause an annual loss of USD 49.85 million in wheat, with global losses estimated at 5–9% [11]. Before the Green Revolution, wheat was considered largely free from serious insect pests, with only the Gujhia weevil (Tanymecus indicus Faust) and grasshopper (Chrotogonus spp.) regarded as significant threats. However, the introduction of high-yielding semi-dwarf varieties, the increased use of inorganic fertilizers and pesticides, and advancements in production technologies have disrupted natural predator–prey balances, leading to pest outbreaks [12]. The shift to a monoculture rice–wheat cropping system further intensified pest pressures, as most wheat pests are either oligophagous or polyphagous, and this system provides a continuous food source that favors their buildup. As a result, new pests such as termites, aphids, armyworms, gram pod borers, and brown wheat mites have emerged as major threats [13,14,15]. Consequently, insect-induced yield losses in wheat have risen from an average of 3% in the pre-Green Revolution era to 5% in the post-Green Revolution era in India [16,17,18]. Furthermore, the continuous rice–wheat cropping system in the Indo-Gangetic Plains (area comprising Punjab, Haryana, Uttar Pradesh, Bihar, and West Bengal) has exacerbated pest pressures [19,20]. Mode of damage, and factors associated with increased incidence of major insect pests affecting wheat in North India are presented in

Table 1. The main herbivorous insect pests affecting wheat crop in the North India.

Pests	Common Name	Insect Species	Part Infested and Damage	Factors Associated with Increased Incidence	References
Soil and root pests	Termites	Microtermes obesi Holmgren, Odontotermes obesus Rambur	Cuts the roots and underground stem portion of plants; drying of plants	Raised bed sowing	[21,22]
	Root aphid	Rhopalosiphum rufiabdominalis Sasaki	Sucks sap from roots and crown region of stem; stunting of plants	Loose soils	[19]
Leaf-feeding pests	Corn leaf aphid Bird cherry-oat aphid English grain aphid Indian grain aphid	Rhopalosiphum maidis (Fitch) Rhopalosiphum padi (Linnaeus) Sitobion avenae (Fabricius) Sitobion miscanthi (Takahashi)	Sucks sap from leaves, stem and earheads; leaf discoloration and stunting; injects toxins and transmit barley yellow dwarf virus	Irrigated conditions	[22,23,24]
	Brown wheat mite	Petrobia latens (Muller)	Feeds on leaf tips and damages the plant cells; stippling of leaves; death of plants	Rainfed conditions	[22,25]
	Oriental armyworm	Mythimna separata (Walker)	Feeds on leaves of seedlings and earheads; defoliation	Fields with large loads of paddy straw	[21,26]
Stem-borer pests	Pink stem borer	Sesamia inferens Walker	Bores into the stem and kills central shoots; dead hearts	Fields that contain rice stubble	[13,19]
Earhead pests	Gram pod borer	Helicoverpa armigera (Hubner)	Feeds and destroys grains in the earheads	Fields where cotton–wheat rotation occurs	[21,26,27]

.

Additionally, recent changes in climate, such as elevated temperatures and erratic rainfall patterns, are likely to amplify spatiotemporal variations in both abiotic and biotic stresses for wheat producers, leading to significant spatial changes in yield and grain quality [28]. This includes anticipated alterations in pest physiology and survival rates during heat waves or frosts, population growth dynamics and geographical range for insects, host-range expansion and shortened crop cycles [29,30,31]. For instance, warmer winters may increase the number of aphid generations within a single wheat growing season [32]. As temperatures rise, pests and pathogens are expected to spread beyond their traditional habitats; for instance, the English grain aphid, Sitobion avenae (Fabricius) has already expanded its range to cover nearly the entire Northern Hemisphere [33].

In recent years, to mitigate the adverse effects of residue burning on the environment, there has been a shift from conventional to conservation agriculture in North India. The adoption of residue management practices, such as using the Happy Seeder for sowing wheat in standing paddy stubbles, has inadvertently increased the prevalence of sporadic pests in wheat fields in North India. Such pests like pink stem borer (Sesamia inferens Walker), armyworm (Mythimna separata Walker), and root aphid (Rhopalosiphum rufiabdominalis Sasaki) have emerged as significant threats [14,17]. According to Singh et al. [34], 43% of farmers have reported moderate to severe pest issues in wheat crops grown with residue retention. This change in pest dynamics has also increased the cost of insecticide application by USD 8.6 per hectare (ha) in residue-retained wheat crops compared to those without residue [35].

The rapidly growing world population and urbanization has led to a significant surge in the demand for improving wheat production, which must rise at an annual rate of 2% despite limited land resources [36,37]. However, wheat yields are only increasing at a rate of 0.9% annually, falling short of the 2.4% needed to double global production by 2050 [38]. Kumar et al. [39] projected a reduction of 6–23% and 15–25% in wheat yield in India during the 2050s and 2080s, respectively, under projected climate change scenarios. Although disease-resistant varieties have been effective against wheat diseases like rust, chemical control remains the primary and most effective tool under high insect pest-pressure scenarios in wheat. To meet food security demands, substantial amounts of chemical fertilizers and pesticides are applied, elevating environmental issues, and contributing to pest resurgence due to economically misguided chemical control practices [40]. Indiscriminate pesticide use is costly, ecologically unsustainable, and leads to insect resistance development [41]. Therefore, it is crucial to explore alternative and more sustainable pest management practices that minimize these drawbacks while ensuring crop protection. Given the imperative to increase wheat productivity without expanding agricultural land area or intensifying water and fertilizer use, climate-smart innovative pest management techniques integrating interdisciplinary methodologies need to be developed. These approaches, aimed at reducing crop losses caused by various insect pests, should also enhance ecosystem services, and bolster the resilience of agricultural systems in response to climate change challenges. Implementing an integrated pest management (IPM) framework is essential in creating effective and resilient production systems. Like with other agricultural crops, IPM modules for wheat integrate diverse strategies including cultural, mechanical, biological, and refined chemical approaches, tailored to meet growers’ needs and address pest issues [20,42]. This review discusses the bio-ecology and current management practices of key wheat pests in North India, highlighting future challenges related to wheat IPM in this region.

2. Major Wheat Pests: Bio-Ecology and Their Management Strategies

In North India, wheat is sown during October–November and harvested in April. The primary insect pests currently causing economic damage at different growth stages of wheat (Figure 1 and Figure 2) include foliar aphids: corn leaf aphid (Rhopalosiphum maidis), bird cherry-oat aphid (Rhopalosiphum padi), English grain aphid (S. avenae), and Indian grain aphid (Sitobion miscanthi); termites (Microtermes obesi and Odontotermes obesus); oriental armyworm (M. separata); pink stem borer (S. inferens); gram pod borer (Helicoverpa armigera); brown wheat mite (Petrobia latens); and root aphid (R. rufiabdominalis). Among these, foliar aphids and termites are the most common and significant pests in this region. However, the pink stem borer and root aphids, traditionally pests of rice (Oryza sativa L.), are emerging as significant threats to wheat as well [17,43,44].

2.1. Aphids

2.1.1. Pest Description

Aphids (Hemiptera: Aphididae) are one of the major pests affecting agricultural crops including wheat globally, with more than 250 species known to infest both row and horticultural crops [45]. Globally, 64 aphid species are reported to colonize the bread wheat; however, the wheat crop is attacked predominantly by four aphid species viz. R. maidis (Corn leaf aphid), R. padi (Bird cherry-oat aphid), S. avenae (English grain aphid), and S. miscanthi (Indian grain aphid) in India. These aphid species are known to cause yield loss by directly (3–21%) sucking the plant sap and/or indirectly (20–80%) by transmitting fungal and viral diseases [46]. The cultivation of high-yielding Mexican varieties, coupled with increased use of fertilizers and irrigation, has contributed to the heightened prevalence of aphids [47]. Additionally, R. rufiabdominalis has been documented infesting wheat roots [48]. Recently, the potato aphid, Macrosiphum euphorbiae Thomas, initially a pest of solanaceous crops, has been reported in association with wheat crops in North India [49]. Interestingly, aphid species exhibit distinct feeding preferences on wheat. R. padi infests all above-ground plant parts, with a higher prevalence on leaves and stems. R. maidis is confined solely to leaf whorls. S. miscanthi infests leaves and earheads and is the dominant aphid species on earheads [50].

Both adult and nymph aphids damage wheat plants by sucking cell sap, reducing the vitality of the plants. Infested plants exhibit pale and silky leaves and eventually wilt. Aphids also excrete honeydew, leading to the development of black sooty mold on leaves, which reduces the photosynthetic activity [51]. Infestation often starts from the field’s periphery, particularly where trees are planted [52]. Key feeding areas for aphids on wheat plants include the flag leaf sheath, main stem, and immature kernels during the flowering stage, resulting in the death of spikes, and shriveled or empty grains. Aphid saliva causes yellow or whitish streaks on leaves [51]. Heavy infestations can lead to stunted growth, reduced leaf size, bleached spikes, purplish streaks on tillers, loss of dry weight, and reduced chlorophyll content due to disruptions in the electron transport chain in leaves [53,54,55]. Late-sown wheat experiences higher aphid populations during the vegetative phase, while wheat sown in a timely manner has more aphids on earheads during the reproductive stage [56]. The economic threshold level for aphid infestation is set at five aphids per earhead, determined by observing ten randomly chosen earheads from each of the four sections in a one-acre field [21]. Furthermore, foliar aphids transmit barley yellow dwarf virus (BYDV), which causes severe damage to the crop [57]. BYDV is transmitted by three aphid species, i.e., R. maidis, R. padi, and S. avenae [24].

2.1.2. Bio-Ecology and Management

Adult aphids are soft-bodied and range in color from green to black, typically living in small colonies on leaves and spikes. They exhibit various stages, including winged (alates) and wingless (apterous) sexual and asexual forms [58]. Aphid infestations typically start from January until crop maturity, with the most severe damage observed during February-March when ears are ripening [58]. Their rapid spread is facilitated by asexual reproduction, where viviparous females directly give birth to nymphs rather than laying eggs. Rhopalosiphum padi reproduces parthenogenetically for several generations before switching to sexual reproduction [27]. Sitobion miscanthi reproduces year-round through viviparous parthenogenesis, while S. avenae can reproduce both sexually and parthenogenetically [58,59]. During autumn, alates fly to primary hosts such as Cynodon dactylon in the case of S. avenae to mate and lay eggs, without producing any visible feeding symptoms [27,58]. Aphids go through four nymphal instars, each lasting around 2–3 days, completing their development cycle in 7–8 days depending on temperature conditions. They can produce over 10–15 generations per season. Wingless forms produce more offsprings than winged forms but have a shorter lifespan. In the field conditions, viviparous wingless forms are common and present in large numbers [58]. While alate forms aid in long-distance movement and develop in response to food and space shortages, apterous forms physically damage the plant by sucking sap from young leaves, which leads to leaf distortion [27,52]. The rate of development, number of offspring, and adult lifespan are influenced by the type of host species, its age, and temperature conditions. Cold and dry weather conditions favor rapid reproduction, resulting in population explosions [27,60]. Temperature and the plant’s growth stage play crucial roles in aphid population dynamics. The minimum threshold temperature for nymphal development is 1.57 °C, while the highest intrinsic growth rate occurs during the wheat jointing stage at 18–21 °C. However, excessively high temperatures can reduce aphid survival and spread [27].

To control aphids, cultural, physical, mechanical, biological, chemical, and host plant resistance methods can be used. Singh and Singh [23] reported that the early sowing of wheat helps escape peak aphid attacks, while timely and late sowing wheat coincides with peak populations. Installing sticky traps at a rate of 12 to 15 per hectare for monitoring aphid incidence is recommended. Yellow sticky traps are more effective than blue traps [61,62]. Additionally, the zero-tillage system for sowing wheat can help reduce aphids. Compared to conventional tillage, zero-tillage often leads to sparser crop growth, which is less attractive to foliar aphids. The surface residues left in the field can also act like reflective mulch, making it harder for aphids to settle on the crop [22]. Reduced tillage has also been shown to limit root aphid damage. Increased soil compaction and lower porosity under this system restrict aphid movement, resulting in reduced infestation levels [19]. Chaudary et al. [63] evaluated a push and pull strategy for managing aphids in wheat and found that peas as a trap crop proved beneficial in reducing foliar aphid population from main crop without aid of pesticides. This effect is likely due to the pea crop attracting a higher abundance of natural enemies, such as lady beetles and parasitic wasps, which help regulate foliar aphid populations more effectively than in wheat monocultures. Additionally, intercropping may disrupt aphid host-finding ability, as volatiles from non-host plants (i.e., pea) can mask or overlap with wheat odors, reducing colonization [64]. Resistance to R. padi and S. avenae has also been identified in T. monococcum wheat genotypes MDR045 and MDR049 under field conditions, thus this resistance can be incorporated into commercial wheat varieties [65]. Singh and Singh [66] screened advanced breeding lines of wheat and observed moderate resistance to foliar aphids in lines HI 8823(d), DBW 317, MACS 6774, PBW 873, DBW 378, HD 3386, and UAS 310. Similarly, R. padi number, weight, survival, and reproduction potential was significantly lower on resistant lines viz., W064 and W068 [67]. Additionally, Sharma and Singh [68] reported that R. padi resistance in Aegilops tauschii accessions, i.e., PAU 14232 and PAU 14576 involves combination of antixenosis and antibiosis resistance mechanisms.

Under favorable weather conditions, aphids may reach devastating levels through asexual reproduction, such that chemical control often becomes necessary [44]. As the aphid incidence starts from periphery spraying border rows to control their spread into the interiors of wheat field is recommended. Spraying of thiamethoxam 25 WG (50 g/ha) or 5% neem seed kernel powder when aphid infestation exceeds economic threshold level is suggested [21,61]. Similarly, a study by Pathania et al. [69] found that the reduction in aphids using an aqueous neem extract (5 L/ha) and neem seed kernel extract (10%) was comparable to the reduction achieved with thiamethoxam; thus, neem (Azadirachta indica L.) can be a good eco-friendly alternative to synthetic pesticides. Moreover, Katare et al. [70] found that foliar application of sulfoxaflor 12 SC (24, 27 and 30 g active ingredient (a.i.)/ha) resulted in 94.54, 95.27 and 96.03% reduction in aphid populations, respectively, with 30 g a.i./ha being the most economical. A variety of natural enemies including different lady beetle species, hoverflies, parasitic wasps, and green lacewings attack aphids in wheat fields (Figure 3). Among these, the seven-spotted lady beetle (Coccinella septempunctata) is the most commonly observed predator of aphids in wheat. Important parasitoid wasp species include Lysiphlebus testaceipes, Diaeretiella rapae, and Aphelinus varipes. The larvae of green lacewings (Chrysoperla carnea) also feed primarily on aphids, although they are less frequently encountered in wheat ecosystems. These beneficial insects collectively help suppress aphid populations and prevent them from reaching economically damaging levels [27].

2.2. Termites

2.2.1. Pest Description

Termites are polyphagous social insects that belong to the order Blattodea and infra-order Isoptera, believed to have evolved around 220 million years ago from primitive wood-dwelling cockroaches [71,72]. They are classified into 12 families based on morphology and symbiotic relationships, with about 75% belonging to the largest family, Termitidae [73]. They live in highly organized colonies known as termitaria, with different castes such as workers, soldiers, and reproductive individuals [52]. Among the 300 termite species considered pests worldwide [74], about 35 species cause significant damage to both agricultural crops and infrastructure in India [75], leading to annual losses estimated at USD 35.12 million [76].

Ecologically, termites play a crucial role as major recyclers of lignocellulosic biomass from both live and dead plant material [73]. Termites are capable of degrading wheat straw lignin and polysaccharides with the help of their gut microbial symbionts [77]. Termites depend on enzymes secreted by intestinal protists like Mixotricha sp., and Trichonympha which are in turn associated with prokaryotes such as Bacillus sp., Enterobacter sp., Ochrobacterium sp., and Treponema sp. [73,78]; for the biodegradation of wheat straw [77]. Additionally, Termitomyces sp. fungus is cultivated within termite nests of higher termites, providing a protein-rich food source for the queen, king, and young termites [52,73].

Wheat is particularly susceptible to termite attacks throughout its growth stages with higher damage in rainfed and sandy soils than irrigated regions in India [21,75]. In particular, Odontotermes obesus and Microtermes obesi are the most destructive termite species of wheat in India, resulting in 43 to 80% yield losses [79,80,81]. Other termite species attacking wheat in North India include Odontotermes gurdaspurensis Holmgren and Holmgren and Microtermes mycophagus (Desneux) [82]. Overall, the damage due to termites can vary between 29 and 100% [83,84]. Termites feed on the roots and underground stem portions of plants at the seedling stage, typically 3–5 weeks after emergence [34,52]. Affected plants wither entirely and can be pulled and uprooted effortlessly, creating patchy gaps due to seedling death [52]. When termites attack plants during later growth stages, it leads to the development of white ears containing no grains.

2.2.2. Bio-Ecology and Management

Termites undergo the process of incomplete metamorphosis and complete their life cycle in three stages, i.e., egg, nymph, and adult [73]. Each termite colony is established and dominated by one queen and king. The queen can be up to 70 mm long while the king can be 10–20 mm long [52]. The queen lays thousands of eggs after mating in a nuptial chamber [85]. The eggs are generally dull, kidney-shaped, laid singly, and hatch in about 30–90 days. The nymph resembles the adult but are smaller in size and molts eight to nine times within 6–12 months to develop into a cream-colored adult with a dark-colored head [26,52]. The nymphs can either molt into workers or soldiers. A worker’s life span varies between 1 and 2 years with a mature colony comprising 200,000–2,000,000 workers [85]. Periodically, nymphs produce alate forms that swarm out for nuptial flights, typically during the monsoon season when the soil is wet from rain and therefore more easily penetrated by termites [26,52]. After mating, alates shed their wings and nest is established, and the abdomen of queen becomes substantially larger with thousands of eggs which upon oviposition hatch into young termites [52,86].

Insecticides remain the primary strategy for termite management in wheat crops worldwide [87]. Cultural methods to prevent termite infestation include destroying or burning crop residues, deep summer plowing to expose termite mounds and tunnels to sunlight and predators, flood irrigation, and application of fully decomposed farmyard manure [88]. The high-density sowing of wheat is also suggested, with appropriate thinning of plants that survive termite damage [27]. Termite damage is significantly higher in the early-sown crop compared to the timely-sown and late-sown crops, hence avoid early sowing of wheat in areas where termite infestation is a problem [23].

Amongst the chemical methods, seed treatment is quite efficacious against termites. Particularly, seed treatment with 4 mL of chlorpyriphos 20 EC or 1 g thiamethoxam 70 WS per kilogram (kg) of wheat seed is recommended before sowing wheat. Additionally, broadcasting 50 kg soil per hectare treated with 3 L chlorpyriphos 20 EC or 17.5 kg fipronil 0.3 G, followed by light irrigation can be practiced under severe infestations [21]. A study performed under semi-arid irrigated conditions in southwestern Punjab observed that seed treatment with thiamethoxam at 1 g/kg seed and broadcasting fipronil 0.3 G at 20 kg/ha significantly reduced damaged tillers per meter row compared to other treatments resulting in higher grain yields and relatively fewer harmful effects on natural enemy populations [89]. Additionally, Singh and Bala [90] reported that a pre-mixed combination of imidacloprid 18.5% + hexaconazole 1.5% at 2 mL/kg of wheat seed did not adversely affect germination, effectively reduced termite infestation, increased seed yield, and eliminated the need for separate treatments for termites and smuts. Mukhopadhyay et al. [91,92] evaluated a Steinernema abbasi-nematode enriched bioinsecticidal powder under field conditions and found a significant reduction in termite damage in wheat fields compared to the synthetic insecticide (chlorpyriphos 20% EC). In treated plants, agronomic traits such as plant height, spike weight, and number of spikelets per spike were also positively influenced, validating its potential as an effective biopesticide for organic farming and integrated pest management.

2.3. Oriental Armyworm

2.3.1. Pest Description

The oriental armyworm, Mythimna separata Walker (Lepidoptera: Noctuidae), is a defoliator pest that widely affects wheat crops in the Indo-Gangetic plains, including regions like Punjab, Haryana, Himachal Pradesh, and Uttar Pradesh [21,93]. It is a typical long-distance migratory insect that became a regular pest of late-sown wheat during the late 20th century and has caused huge economic losses since then [94,95,96]. Caterpillars are the only destructive stage in its life cycle [97] as they are capable of feeding on more than 300 plant species belonging to 100 families, i.e., rice, maize, sorghum, barley, sugarcane, and a variety of grasses [52,98,99]. The pest is called “Armyworm” due to its tendency to spread in a line across fields, consuming foliage as it moves, thus resembling a slow march. The larvae, after devastating one field, migrate to another field such that the field looks as though it has been subjected to cattle grazing [60]. Newly hatched larvae consume tender leaves while mature larvae feed on leaves, flag leaves, and ears, including awns and immature grains, and can cause up to 40% yield reductions [52,100]. Moreover, under severe infestations larvae may climb up to cut the stem just below the earhead [58]. Therefore, its outbreak may lead to complete crop loss depending upon the stage of crop [95]. Armyworm larvae hide during the day in stubbles or tillers, feeding at night or early morning. In moist conditions, they might feed during the daytime also [58]. However, pest attacks can be detected by spotting larvae and dark green fecal pellets near the plant’s stem. Armyworm infestations are more prominent in rice–wheat cropping systems [14,52]. This pest typically attacks wheat crops during March–April, but recent damage has also been reported in December in Happy Seeder + Mulcher-sown wheat or fields with large paddy straw loads [21,34].

2.3.2. Bio-Ecology and Management

Adults of armyworm are robust and tan colored with dark specks [15]. They are smaller than other cutworm-armyworm moths, measuring around 12 mm in length with a wingspan of 25–40 mm [52]. Forewings are grayish-yellow with circular and reniform spots having indistinct margins. The outer wing margin is obliquely blackened from the top rearward, featuring a dark streak and a row of dark spots. Hind wings are gray, with dark outer margin. Antennae are thread-like. Female moths lay about 500 eggs [58]. The eggs are round, shiny with fine reticulations and are deposited on the leaf surface in groups [52,101]. The hatching period ranges between 4 and 11 days in summer and 19 days in winter [26]. Upon hatching, the neonate larvae are very active and start feeding on the seedling leaves, thus its color changes from pale to light green. The larval stage is 13–14 days long during spring, but ranges between 88 and 100 days during winter and includes 6 instars [26,52]. Mature larvae are 30–40 mm long, green to pink with longitudinal light gray to black stripes and have a brown to orange head marked with an A-shaped pattern [102]. Pupation typically occurs in the soil at a depth of 0.5–5 cm, though it can also take place beneath dry leaves and lasts for about 9–13 days in May and 36–48 days in the winter. Thus, the life cycle is completed in 30–35 days and is repeated many times in a year [26]. The pest is capable of surviving on summer season crops like rice and continues to survive in the stubbles [58]. Extended drought periods followed by heavy rainfall increase its population [95].

To control armyworm, the foliar application of 1 L of quinalphos or 100 mL of chlorantraniliprole 18.5 SC in 200–250 L of water per hectare is effective in wheat crops. These insecticides will also control aphids. To enhance insecticide efficacy, applications should be carried out in the evening when armyworm larvae are most active. Alternatively, 17.5 kg of fipronil 0.3 G or 2.5 L of chlorpyriphos 20 EC mixed with 50 kg of moist sand can be spread across one hectare before first irrigation [21]. Singh and Sarao [103] observed that foliar application of chlorantraniliprole and soil application of fipronil are effective for managing armyworms in the early stages of wheat. However, commercial Bt formulations showed relatively less reduction in damage, with a 47–51% reduction observed over 14 days. Biocontrol agents are also efficacious for controlling this pest. For instance, the stink bug Andrallus spinidens (F.), found in the Kumaon region of Uttarakhand, preys on armyworm in wheat so can be exploited for biocontrol interventions [104]. Entomopathogenic nematode Steinernema carpocapsae causes significant mortality in second and fourth instar larvae under laboratory conditions, achieving 100% mortality in larval stages and 75% in pupal stages [105]. Similarly, in a laboratory study, the third and fourth larval instars of M. separata were highly susceptible to Heterorhabditis bacteriophora strain S15 EPN infection, with the highest mortality rates of 96% and 98%, respectively [106]. Ji et al. [107] exploited the use of RNAi to target and suppress the clock gene Msper, reporting a significant reduction in M. separata flight and reproductive activities. Thus, gene silencing can be developed as a novel pest control method against M. separata thereby decreasing its population and impact.

2.4. Pink Stem Borer

2.4.1. Pest Description

The pink stem borer (PSB), Sesamia inferens Walker (Lepidoptera: Noctuidae) is a polyphagous pest that is prevalent in South and Southeast Asian countries [60]. Some important hosts of this pest are rice, wheat, sugarcane, oats, maize, sorghum, and pearl millet [52]. The PSB feeds on rice from July to October in North India and then migrates to wheat crops. Infestation rates of 5.7–11.10% have been observed in wheat [108]. The incidence of PSB is increasing due to adoption of zero tillage system for sowing wheat [109,110]. Early sown wheat shows heavier PSB incidence than late sown crop [21,27]. Furthermore, the continuous rice–wheat cropping rotation in the northwestern plains of India, coupled with mild winters and a reduced fallow period between rice harvest and wheat sowing, has heightened the incidence of this pest in the region [111]. It attacks the wheat crop at seedling stage and can cause up to 50–60% damage [52,111]. The larva bores into the stem of the young plant and kills the central shoot thereby causing ‘dead heart’ symptoms. Upon destroying one young wheat tiller, the larva subsequently starts feeding onto adjacent tillers. Nonetheless, damage is confined to a few areas in a wheat field and does not follow any random distribution. However, if the larvae attack the wheat plant at heading stage, ‘white ears’ are produced [13,110].

2.4.2. Bio-Ecology and Management

The adult moth is small, stout, and straw-colored with a wingspan of about 28 mm [112]. While the hind wings have 3–4 veins and are white in color, the forewings have a reddish-brown suffusion along the median nervure with 2–5 veins [113]. The pest exhibits sexual dimorphism as in males the antennae are hairy/ciliated while females have simple antennae [113,114]. The adult female lays creamish-white eggs arranged in several rows under the leaf sheath. Occasionally, eggs can also be found positioned at the crown of wheat plants, on the soil or in the leftover stubbles of rice plants [112]. The larva hatch within 7–10 days and immediately bores into the stem to feed on internal tissues. The larval stage lasts up to 20–30 days and comprises 8 larval instars. Fully grown caterpillars have brown heads and pinkish 30–40 mm long cylindrical bodies with pink and buff markings [26,52,113]. They pupate in the stem of the wheat plant for 8–10 days [26]. Male pupa is about 10.5–12 mm long and 2.5–3 mm wide possessing two pads guarding the 9th sternite. In contrast, the female pupa can be 15.5–17.5 mm long and 3–4.5 mm wide, with a bursa copulatrix located on the 8th sternite [114]. The life cycle of this pest typically spans 40–70 days with 4–6 generations in a year influenced by the prevailing climatic conditions [26]. The larva remains dormant in winter and hibernates in rice stubbles [115].

Sowing wheat in October can be discouraged in fields with severe PSB infestation in the preceding rice crop. Additionally, the removal and destruction of the rice stubbles at the time of first plowing after the harvest of rice crops also reduces the pest being carried over to the wheat. Fields can be irrigated, preferably during daytime, as this enhances insect predation by birds [21,58]. Moreover, Singh and Singh [23] investigated the effect of sowing dates on PSB, finding that PSB incidence was significantly higher in early-sown wheat (7.35%) compared to timely-sown (5.97%) and late-sown (3.01%) crops. Additionally, Muhammad et al. [116] demonstrated that the appropriate management of rice stubbles, particularly using a rotavator as a tillage tool before sowing wheat, significantly reduces the incidence of PSB in the wheat crop. In case of severe infestation, the soil application of 17.5 kg of fipronil 0.3 G or 2.5 L of chlorpyriphos 20 EC mixed with 50 kg of moist sand per hectare can be performed before first irrigation. Alternatively, the foliar application of 125 mL of chlorantraniliprole 18.5 SC in 200–250 L of water per hectare is also effective [21]. Similarly, fipronil 0.3% GR applied at 20 kg/hectare resulted in the maximum reduction in tiller damage and higher grain yield of wheat in the districts of Amritsar and Gurdaspur, located in the northwestern part of Punjab [117]. Timbadiya and Sisodiya [118] reported that chlorantraniliprole 18.5 SC at 0.006% resulted in the highest grain and straw yields and was similarly effective to Spinosad 45 SC in reducing dead heart percentage due to PSB in durum wheat. They also observed that seed treatment with chlorpyriphos 20 EC provided the highest incremental cost–benefit ratio, followed by chlorantraniliprole 18.5 SC and spinosad 45 SC. Soil application of diatomaceous earth (silicon source) at 300 kg/ha is more superior in reducing PSB population than conventional insecticides and improves wheat yield by enhancing total sugars, total phenols, antioxidant, and defensive enzyme activities [119]. Pawar et al. [120] investigated the effectiveness of octadecane, a plant herbivore induced volatile in combination with egg parasitoid Trichogramma chilonis releases, finding that it dramatically minimizes the damage caused by PSB by increasing the biocontrol potential of T. chilonis.

2.5. Gram Pod Borer

2.5.1. Pest Description

Helicoverpa armigera Hubner (Lepidoptera: Noctuidae), commonly known as the cotton bollworm, gram pod borer, corn earworm, or Old World (African) bollworm, is a highly polyphagous and sporadic pest of wheat and other crops. It affects over 181 plant species across 68 diverse families, including important crops such as cotton, sunflower, rice, maize, sorghum, tomato, chickpea, and other legumes [121,122,123,124,125]. This pest is distributed throughout Asia, Europe, Australia, and Africa [122,126] and is considered one of the most damaging insect pest species globally, with an estimated global loss exceeding USD 3 billion annually [125]. In India, this pest affects around 96 different crops and causing annual monetary losses of up to USD 2 billion [127]. It has been reported as a regular pest on wheat in Punjab, Haryana, Delhi, Uttar Pradesh, Rajasthan, Gujarat, and Jammu and Kashmir [128].

Helicoverpa armigera’s notoriety stems from its polyphagy and the strong migratory abilities of its adults, capable of traveling up to 2000 km [129,130,131,132]. It is highly fecund, with rapid reproduction rates, completing 4–6 generations per year in most cropping regions, and up to 10–11 generations in some tropical climates [133,134,135]. Larvae are aggressive feeders, preferring reproductive structures but also consuming vegetative parts when necessary [136]. The pupae can enter facultative diapause during unfavorable conditions [135]. In wheat, a single caterpillar per tiller can cause a yield loss of 13.98% [137]. Young larvae consume leaves, while mature larvae feed directly on grains within heads, hollowing out internal tissues [26,52,138]. Additionally, its adults feed on wheat pollens, and first-generation larvae feed on wheat, while corn and cotton serve as hosts for subsequent generations [139]. The infestation rate on heads is up to 15%, but the grain damage on infested heads is about 3.90% [138].

2.5.2. Bio-Ecology and Management

Helicoverpa armigera is a holometabolous insect, which means that it has four major stages, the egg, larva, pupa, and adult [140]. The female moth lays 600–800 yellow ribbed eggs individually on the tender parts and buds of plants during the early evening hours [26,52,141]. The eggs are pomegranate shaped and 0.4–0.6 mm in diameter [140]. After 24 h of egg laying, a dark red or brown ring is developed on top of the eggs, which fully darken prior to hatching [52]. The eggs hatch in 2–4 days, and the caterpillars are initially brown and later turn green with dark broken lateral and dorsal stripes [26,141]. The larval stage comprises 4–6 instars and is completed in 28–35 days [52]. Fully mature larvae stop feeding and migrate to the soil for pupation. The pupa is dark brown in color and measures around 19 mm in length. The pupal stage lasts for 12–16 days [27,52]. Adult moths are strongly built and are 14–19 mm long with a wingspan ranging between 35 and 40 mm. Forewings are black or dark brown with kidney-shaped markings at the center. Hindwings display a gray band along the outer edges and are cream-white. Adults exhibit sexual dimorphism as male moths are yellowish-brown, while female moths are orange-brown in color [27]. The adults have a lifespan of 12–16 days [52]. Helicoverpa armigera is more prevalent in fields following a cotton–wheat rotation, typically infesting wheat near maturity, i.e., during March–April [21,27]. Staggered sowing and frequent irrigation can lead to heavy pest incidence [26]. However, wheat does not suffer significant harm from this pest and can act as a bridge host for H. armigera, facilitating its carry-over [26].

Protecting crops from H. armigera infestations is a significant challenge due to its polyphagous feeding behavior, extensive host range, ecological plasticity across diverse agro-climatic regions, and its demonstrated capacity to evolve resistance to multiple classes of chemical insecticides [142]. Despite various control measures, chemical control using synthetic and semi-synthetic insecticides remain the most widely used method. Approximately 50% of the total insecticide applications in India and China target H. armigera [143]. Nevertheless, regular pest population monitoring using light traps, pheromone traps, and in situ assessments at various levels is essential for its effective management [144]. Cultural practices like crop rotation with non-host crops and growing intercrops or barrier crops can minimize pest incidence [27,58]. The foliar spray of quinalphos at 2 L in 250 L of water per hectare is recommended for pest control in wheat crops [21]. Additionally, emamectin benzoate shows significant systemic toxicity on H. armigera larvae, making it a promising tool for IPM [145].

Furthermore, plant-derived products and biorational insecticides are being researched for their eco-safety and effectiveness in reducing pod borer growth and reproduction [146]. For instance, β-sitosterol a compound present in the stem extracts of Thevetia neriifolia has shown potential in inhibiting H. armigera growth by causing systemic toxicity and reducing midgut enzyme activities [147]. da Costa Inacio et al. [148] reported the use of tagitin and C-enriched leaf extract of Tithonia diversifolia provided high insect mortality, and antifeedant activity against H. armigera larvae. Furthermore, synergistic effects have been observed with a 1:1 combination of β-sitosterol and triflumuron, a chitin biosynthesis inhibitor, significantly inhibiting H. armigera larval growth and adult emergence [149]. These compounds can be promising alternatives to synthetic insecticides.

Various natural predators and parasitoids also play a crucial role in regulating Helicoverpa populations. These natural enemies can maintain pest levels below economic thresholds without insecticides [140]. Common natural enemies include hemipterans, coleopterans, chrysopids, ants, spiders, flies, and parasitoids wasps like Microplitis, Trichogramma, Telenomus, and others [150]. Moreover, the stink bug A. spinidens, found in the Kumaon region of Uttarakhand, preys on lepidopteran larvae, including H. armigera in wheat [104].

2.6. Brown Wheat Mite

2.6.1. Pest Description

The brown wheat mite (BWM), Petrobia latens, Muller 1776 (Acari: Tetranychidae), is a serious pest of dryland agriculture [151]. It is prevalent in the warmer regions of central India, extending somewhat into the northern plains. In Madhya Pradesh, Haryana, Delhi, Rajasthan, Punjab, and western Uttar Pradesh, it poses a significant threat to unirrigated wheat fields [152,153]. Damage is always associated with drought stress [154]. It was first documented on cumin in Rajasthan [155]. It can feed on onion, garlic, wild oat, melon, cucumber, coriander, carrot, strawberry, gladiolus, cotton, barley, lettuce, apple, lucerne, rice, and sorghum in addition to wheat [52]. It is mainly found on the upper surface of leaves [154]. Both adults and nymphs suck plant sap by inserting their needle-like stylets into the leaf blades, sheaths, green stem, and spikes [152]. Affected plants display a pale yellow/bronze appearance with stippling on leaves. Severe damage is inflicted on the lower leaves of wheat and barley, leading to iron deficiency and desiccation [156]. Mites start feeding from leaf tips, causing leaves to dry and die from the tip downwards. Infested fields look scorched and withered under heavy pest pressure. As a result of feeding, plants become chlorotic, resulting in unhealthy grain formation, but BWMs do not spin webs on the leaves [26]. The affected grains shrink and appear shriveled, thus losing their cosmetic and market value [52]. BWMs also transmit barley yellow streak mosaic virus on recrops of barley under dry conditions [154].

2.6.2. Bio-Ecology and Management

Mites are microscopic, measuring approximately 0.5 mm in length, with a metallic brown to black body and pale-yellow legs. Their front legs are noticeably longer than the remaining three pairs [61,157,158]. Eggs are typically laid under clods or in crevices, singly or in batches, in active (non-diapause) or dormant (diapause) states. Active eggs are invisible to the naked eye and are red in color, while dormant eggs are white and visible beneath clods. A female can lay 6–10 winter eggs and 1–3 summer eggs daily, resulting in 23–90 winter eggs (red in color) and 8–27 summer eggs (white in color) during her lifetime [158,159]. In cold and wet conditions, active eggs hatch in 9–11 days. Dormant eggs can persist in the soil for extended periods and hatch if wetted, usually in the following spring [26,154]. The nymphs are yellow in color and nymphal stage lasts 8–11 days. Adult females live for 10–20 days and reproduce through parthenogenesis. This parthenogenetic mite can raise three annual generations [159]. Consequently, mite populations often escalate to pest levels in dry conditions. The entire life cycle lasts 25.5 days, encompassing about eight developmental stages [26]. This mite thrives during long-term droughts lasting several years, as well as during extended dry spells within a cropping season [154].

BWM population levels are the highest in March–April in rainfed wheat [61]. Rainfall exceeding 6.35 mm often helps reduce mite populations and alleviate plant stress [27]. However, eggs laid in the soil can still lead to new generations [15]. Mites are active during the day and rest in the soil at night. While the economic threshold is not well defined, more damage occurs if plants are stressed or poorly tillered [52]. Research findings propose an economically justified treatment threshold of 25–50 BWMs per leaf in wheat plants that are 15.24 cm to 22.86 cm tall [27].

Rainfall or irrigation can significantly reduce mite numbers in wheat fields. For the proper management of the BWM, weekly monitoring should focus on field edges and corners where infestations are likely to begin. Managing volunteer wheat is crucial for preventing BWM [154]. Rotating wheat or barley with a non-host crop and deep plowing to eliminate diapausing mite eggs can also be effective. Adjusting planting dates to coincide with unfavorable weather conditions for mites can further help in their control [52]. Numerous natural predators have been reported to be effective against BWM under field environments. Recently, predatory mite viz., Tencateia villosa was reported in association with BWM from Rajasthan, while Anystis baccarum was reported from Punjab, and Himachal Pradesh, especially in dryland areas practicing rainfed farming [160]. Neoseiulus imbricatus is another predatory mite also associated with BWM and widely distributed throughout Punjab [161]. For chemical interventions, thiamethoxam 25 WG @ 50 g/ha or 5% neem seed kernel powder, typically used for aphid control, also helps manage BWM. However, a blanket application of thiamethoxam at the flag leaf stage can reduce coccinellid predators, ultimately increasing BWM populations [61]. Additionally foliar application of propargite at 0.15% have shown strong efficacy [27]. Certain wheat genotypes, such as NW 3069, MACS 6221, VI 924, PDW 315, PDW 317, DBW 46, HPW 308, HPW 309, HI 8692, and WH 1076, have demonstrated moderate resistance to mite infestations [162]. Singh and Singh [66] found that wheat germplasm VL 907, HI 1628, PBW 872, VL 3030, and UAS 310 exhibited the lowest BWM infestations, making them valuable sources for breeding programs focused on BWM resistance.

3. Challenges and Opportunities in Wheat Pest Management Under Changing Agroecological Conditions

Sustaining wheat production amidst changing climate and agricultural practices is crucial for food security. Continuous and large-scale rice–wheat cropping system in North India has intensified insect pest pressure on wheat [22]. The adoption of long-duration wheat varieties to increase the yield potential has reduced the fallow period between rice harvest and wheat sowing, facilitating the migration of pests like PSB and root aphid from rice to wheat crop [17,19,43,44]. Rice and wheat are typically harvested using combine harvesters, which leave stubbles of approximately 30–40 cm. While wheat straw is often salvaged for fodder, rice straw has limited fodder value due to its nutritional composition [163]. Consequently, rice residue has traditionally been disposed of through open-field burning [164]. However, environmental concerns over residue burning have prompted the adoption of conservation tillage, inadvertently increasing the threat posed by pests such as PSB and armyworm in subsequent wheat crops [19,164]. The integration of super straw management systems on combines results in loose straw spread evenly across fields [165,166], which, together with undisturbed stubble in reduced or zero tillage conditions, creates favorable conditions for pest survival. Under conventional tillage, the life cycles of pests are often disrupted through plowing because surviving insect stages are exposed to natural enemies as well as adverse environmental conditions. PSB, once regarded primarily as a rice pest, has now emerged as a cross-crop threat by surviving in rice stubble. In wheat crops sown under zero tillage, more than 70% of PSB larvae persist within underground rice stubble [167]. These surviving populations subsequently shift to wheat during favorable conditions, attacking wheat plants as early as the seedling stage, as illustrated in Figure 4 [19,22]. As a result, PSB incidence is lowest in conventionally sown wheat without residue (0.05%) but higher in residue-retained wheat (0.25%), showing that residue and zero-tillage help the pest survive and infest wheat earlier [110,168].

Similarly, armyworm damage, historically reported during March–April, is now frequently observed as early as December in wheat crops sown under zero tillage conditions, likely due to rice straw residue that shelters the infesting larvae [21,103]. Farmers increasingly report challenges in pest management in residue-retained fields, compounded by shifts in pest occurrence and peak damage periods. Moreover, the timing of insecticide applications has shifted due to changes in the pest bioecology and earlier infestations. Consequently, farmers now need to target PSB in wheat at the seedling stage, while armyworm infestations require treatment as early as December [21,164]. Rice residue not only supports pest survival but also shields larvae beneath the straw, protecting them from both chemical sprays and natural enemies. As a result, insecticides often fail to reach target pests, prompting farmers to increase application rates and frequency to compensate for reduced efficacy, which further disrupts natural biological control. Tillage intensity also influences natural enemy dynamics. Reduced tillage practices benefit resident predators like rove beetles and spiders as these survive well under less disturbed habitats but disadvantage non-resident natural enemies such as wasps and coccinellids which are more attracted to vigorous and green crop plants produced in tilled fields. Thus, tillage practices and residue management strategies directly shape pest dynamics and determine the effectiveness of different biological control strategies [22,169,170,171]. This underscores the need for systematic studies to reevaluate how different residue management systems affect pest biology, seasonal population dynamics and their management.

Climate variations are also impacting insect pest biology and behavior, altering their distribution and severity [172]. Research indicates that pests and pathogens are moving towards the poles due to global warming, expanding their range by 2.7 km per year since 1960 [33]. For instance, drought stress can flare up armyworm infestation in wheat [173]. Similarly, climate change can also influence the efficacy of biocontrol agents. Moreover, due to the changing climate many insect species are shifting to unconventional host plants for survival. Examples of significant pests include the potato aphid, M. euphorbiae, notorious for infesting solanaceous crops, now shifting its host range to wheat fields in New Delhi [49]. Similarly, the heavy incidence of the sugarcane leafhopper, Pyrilla perpusilla Walker, a major pest of sugarcane, has been reported in wheat fields in Chhattisgarh, located in central India [174].

Therefore, when developing IPM strategies, the interaction between the insect pest complex, climate change, and tillage practices must be considered. Robust pest monitoring systems are essential for estimating economic thresholds and detecting secondary and invasive pests to minimize yield losses. Adapting planting systems with increased crop diversity can mitigate climate change effects. Developing pest-resistant cultivars that balance resistance traits with climate resilience is essential for IPM practices. The timely release of stress-tolerant biocontrol agents synchronized with crop phenology, considering climate change-induced stress on their biology, is crucial for effective pest management [175].

Future climate scenarios are likely to exacerbate the wheat insect pest management, potentially reducing the efficacy of current management strategies. To address these challenges, research should focus on developing accurate monitoring systems to predict the impact of climate change on wheat insect pests. Understanding the biology and ecology of these pests in relation to their interactions with crops will provide valuable insights for effective management. Multidisciplinary research on climate change impacts and mitigation strategies is crucial to sustaining global wheat productivity. Proactive strategies, such as frequent pest scouting for early detection and eradication, preventive control measures, and using predictive modeling to forecast potential outbreaks or new introductions, could significantly enhance future of wheat insect pest management.

In addition to climate change, the shift in wheat pest dynamics due to continuous rice–wheat cropping and conservation tillage highlights the urgent need for adaptive pest management strategies. Implementing IPM framework that combines key components like crop diversification, pest-resistant cultivars, and optimizing the use of biocontrol agents is essential. Exploring novel methods such as genetic engineering for development of pest resilient varieties, RNA interference to target vital pest genes, synergistic combinations of biorational pesticides, precision agriculture, and optimizing plant herbivore-induced volatiles for improved biological control are promising avenues for the advancement of wheat insect pest management.