Search Results (51)

Bemisia tabaci is a major pest of open-field melons in Mediterranean regions. Combining several species of natural enemies can improve pest control but it can give undesirable results when the species engage in antagonistic interactions. This study evaluated the effectiveness of Deraeocoris serenus, Orius laevigatus, and Eretmocerus eremicus as biological control agents and the interactions among the species. This was assessed with the presence–absence of all three species combined in a full-factorial assay. Each microcosm consisted of a melon plant grown in a 5 L pot enclosed in fine mesh, with each of the eight treatments replicated four times. Whiteflies were counted on three leaves per plant, and natural enemies were counted on the whole plants over six weeks. Basal leaves were taken to the laboratory and observed for the emergence of parasitoids. All three natural enemies independently significantly reduced whitefly numbers. Deraeocoris serenus was the most effective biocontrol agent, achieving whitefly reductions of more than 100-fold compared to the control. In contrast, O. laevigatus and E. eremicus achieved reductions of approximately 2.4-fold and 3.6-fold, respectively. No additive or synergistic effects in whitefly control were observed when two or more natural enemies were combined. Deraeocoris serenus and O. laevigatus were found to engage in mutual antagonistic interactions, and these two predators also interfered with the parasitoid. In addition, E. eremicus was also found to interfere with D. serenus. Understanding such interactions is essential for optimizing the management of natural enemies and improving biological pest control. Full article

This study examines the impact of fear effects and cooperative hunting strategies in the context of intraguild predation food webs. The presented model includes a shared prey species with logistic growth and assumes that both the intraguild prey and intraguild predator draw their sustenance from the same resource. Using a Lyapunov function enables the system’s global stability to be proven. The impacts of key parameters on system stability are determined through bifurcation analysis. Numerical simulations show that even slight increases in the intensity of fear have drastic impacts on intraguild prey populations and, at higher levels, populations may go extinct. In addition, shifts in the parameter of cooperative hunting have a profound impact on the survival of the intraguild prey. Full article

Our study investigates predation among sympatric owl species in the Judea Region, specifically focusing on the predation by Eurasian Eagle Owls (Bubo bubo) on smaller owl species. Field observations conducted between 2006 and 2009 revealed recurrent predation events, with 172 individuals documented as preyed upon by Eurasian Eagle Owls. These results align with previous studies, demonstrating the role of larger owl species as intraguild predators that affect the survival and reproduction of smaller owls. Our findings emphasize the need for further research on intraguild predation and its ecological consequences. This study contributes to a broader understanding of the complex interactions within nocturnal raptor communities and underscores the importance of incorporating such dynamics into conservation strategies to safeguard owl biodiversity in fragmented landscapes. Full article

The ladybirds Coccinella septempunctata and Harmonia axyridis are important biocontrol agents for the small walnut aphid Chromaphis juglandicola, a key walnut pest. C. juglandicola outbreaks occur in walnut orchards, and walnut yields have declined. Intraguild predation (IGP) is prevalent among natural enemies that coexist in shared habitats and prey upon the same extraguild prey. We designed laboratory experiments to evaluate the potential for IGP between these two ladybirds at different temperatures and extraguild (EG) prey densities, and the ability of IGP to control EG prey under different conditions. We measured IGP rates in first instar larvae, female adults, and male adults (both starved for 24 h) in the vulnerable immature life stages of two ladybird eggs. Intraguild (IG) prey (H. axyridis eggs or C. septempunctata eggs) and EG prey (C. juglandicola) consumption were tallied after 24 h. Temperature and EG prey density influenced IGP rates, with temperature contributing the most to the variance. IGP increased with increasing temperature (15–35 °C), with both factors interactively influencing the EG prey consumption rate and exhibiting highly significant effects. EG prey consumption increased with temperature and density. This research provides theoretical support for the rational use of H. axyridis and C. septempunctata in the joint biological control of C. juglandicola Full article

To date, evaluating the diets of natural enemies like carabids has largely been limited to spatially explicit and short-term sampling. This leaves a knowledge gap for the intra-annual dynamics of carabid diets, and the provision and timing of delivery of natural pest control services. Season-long pitfall trapping of adult carabids was conducted in conventional winter wheat fields, from November 2018 to June 2019, in five French departments. Diagnostic Multiplex PCR of carabid gut contents was used to determine the dynamics of carabid diets. The overall detection rate of target prey DNA was high across carabid individuals (80%) but varied with the prey group. The rate of detection was low for pests, at 8.1% for slugs and 9.6% for aphids. Detection of intraguild predation and predation on decomposers was higher, at 23.8% for spiders, 37.9% for earthworms and 64.6% for springtails. Prey switching was high at the carabid community level, with pest consumption and intraguild predation increasing through the cropping season as the availability of these prey increased in the environment, while the detection of decomposer DNA decreased. Variation in diet through the cropping season was characterized by: (i) complementary predation on slug and aphid pests; and (ii) temporal complementarity in the predominant carabid taxa feeding on each pest. We hypothesize that natural pest control services delivered by carabids are determined by complementary contributions to predation by the different carabid taxa over the season. Full article

Over recent decades, intraguild predation (IGP) has attracted special attention, both from the theoretical and practical standpoints. The present paper addresses the interference competition between two Trichogramma species (egg parasitoids)—on the one hand, the extrinsic interactions (i.e., the indirect competition between female T. achaeae and T. brassicae), and on the other, the intrinsic interactions between the larvae of both species. Furthermore, T. achaeae is a better competitor than T. brassicae due to a dual mechanism—the former acts as a facultative hyperparasitoid of the latter, exclusively considering parasitism relationships as well as presenting predation activity by host feeding, which gives preference to eggs previously parasitized by T. brassicae over non-parasitized eggs. Both mechanisms are dependent on the prey density, which is demonstrated by a change in the functional response (i.e., the relationship between the numbers of prey attacked at different prey densities) of T. achaeae adult female—it changes from type II (i.e., initial phase in which the number of attacked targets increases hyperbolically and then reaches an asymptote, reflecting the handling capacity of the predator), in the absence of competition (an instantaneous search rate of a′ = 9.996 ± 4.973 days⁻¹ and a handling time of T_h = 0.018 ± 0.001 days), to type I (i.e., linear increase in parasitism rate as host densities rise, until reaching a maximum parasitism rate, and an instantaneous search rate of a′ = 0.879 ± 0.072 days⁻¹ and a handling time of T_h ≈ 0) when interference competition is present. These results show that there is a greater mortality potential of this species, T. achaeae, in conditions of competition with other species, T. brassicae in this case. Based on this, their implications in relation to the biological control of pests by parasitoid species are discussed. Full article

Sweet pepper is a crop that benefits from phytosanitary treatments with low environmental impact, especially the successful control of pests through the introduction of biological control agents in greenhouses. However, predators that naturally occur in these surroundings often enter greenhouses. The precise roles of these natural predators and their interactions with the introduced predatory insects and mites are often unknown. This study investigated the relationships between Nesidiocoris tenuis, which is naturally present, and Amblyseius swirskii and Orius laevigatus, which are two species of generalist predators released for the control of multiple pests. This study was conducted for two years on 13 commercial sweet pepper crops in various types of greenhouses (tunnels and traditional greenhouses) in Sicily. The environmental complexity value (ECV) for each site was estimated based on 18 points detected around the site according to the different habitats that occurred at each coordinate. The results showed that the occurrence of N. tenuis in greenhouses, independently of their typology (tunnel or traditional greenhouse), was mainly promoted by the greater diversification of habitats immediately surrounding the pepper crops (in a circular area with a diameter of 500 mt), with an increase in its density during the crop season. Moreover, N. tenuis–O. laevigatus’s co-occurrence in flowers suggested that they were not impacted by each other’s presence and that their co-occurrence had a significant effect on pest reduction, although their co-occurrence was density-dependent. As an intraguild predator, N. tenuis competed with O. laevigatus for Frankliniella occidentalis when many predators were present. In addition, N. tenuis also competed with A. swirskii when they both occurred in flowers at a higher density. This study highlights the importance of pepper plant flowers in promoting a higher occurrence of juvenile forms of N. tenuis within flowers. Amblyseius swirskii colonized the plants in 3 weeks, distributing itself almost uniformly over the leaves with a clear control action against not only Bemisia tabaci but also F. occidentalis when present on the flowers. Thus, this concurrent analysis of several commercial pepper sites within the same production area suggests that, even with similar pest control plans, the diverse variability in the presence of natural enemies must be considered when selecting control strategies for pepper crop pests and that N. tenuis, favored by complex surrounding habitats, contributes actively to pest reduction. Full article

In biological control, joint releases of predators and parasitoids are standard. However, intraguild predation (IGP) can occur when a predator attacks a parasitoid, potentially affecting pest control dynamics. In addition to the focal prey (FP), Trialeurodes vaporariorum, the intraguild predator (IG-predator) Geocoris punctipes can consume the parasitoid Eretmocerus eremicus (IG-prey). In this IGP context with multiple prey, an alternative prey (AP), like the aphid Myzus persicae, may influence interactions. Theory predicts that, in simple interactions, a predator’s functional response (FR) to the FP changes with the presence of an AP. However, whether this holds in an IGP context is unknown. In this study, we empirically tested that prediction. Our results show that without IGP, G. punctipes exhibits a generalized FR with and without AP. Nevertheless, with IGP, the predator exhibited a Type II FR at low and high AP densities, increasing pressure on the FP and potentially favoring short-term biological control strategies. However, when 25 AP were offered, the predator’s response shifted, underscoring the importance of monitoring AP densities to prevent potential disruptions in FP control. In both contexts, the increase in AP produced a handling time increase and a decrease in consumption rate. These results indicate that the theoretical prediction of the effect of AP on the FR is met only under specific conditions, and the complexity of multitrophic interactions must be considered. Full article

Scavenging guilds often have several trophic levels with varying dominance and intra-guild predation, competition, and interaction. Apex predators can control subordinate predators by limiting their numbers and affecting behaviour but also supply a continuous food source by abandoning carcasses. Camera traps monitored the scavenger guild in Alpe di Catenaia, Tuscan Apennine, for three years to determine intraguild interactions and the behaviour response. Wild boar visited most feeding sites but only scavenged in 1.4% of their visits. Red fox was the most frequent scavenger, traded vigilance and feeding equally, and selected low vegetation density, while marten invested more in feeding than vigilance. Marten was the prime follower, appearing within the shortest time after another scavenger had left the site. Red fox occasionally looked upwards, possibly to detect birds of prey. Badger showed scarcely any vigilance, did not feed much on carcasses but scent-marked abundantly. Wolves showed the highest vigilance in proportion to feeding at carcasses among the scavengers. Sites with good visibility were selected by all scavengers except martens who selected poor visibility and new moon illumination. Scavengers were mostly nocturnal, showed weak responses to twilight hours or lunar illumination, and all but red fox avoided human disturbance areas. Full article

The predatory mites Neoseiulus barkeri (Hughes) and the predatory thrips Scolothrips takahashii (Priesner) are known as potential biocontrol agents for the two-spotted spider mite Tetranychus urticae (Koch). These two predator species occur simultaneously on crops in agricultural ecosystems and are proved to be involved in life-stage specific intraguild predation. The intraguild prey may play a role in securing the persistence of the intraguild predators during food shortage periods. To understand the potential of intraguild prey as food source for intraguild predators in the N. barkeri and S. takahashii guild at low T. urticae densities, the survival, development and reproduction of both predators was determined when fed on heterospecific predators. The choice tests were conducted to determine the preference of the intraguild predator between the intraguild prey and the shared prey. Results showed that 53.3% N. barkeri and 60% S. takahashii juveniles successfully developed when fed on heterospecific predators. Female intraguild predators of both species fed on intraguild prey survived and laid eggs throughout the experiment. In the choice test, both intraguild predator species preferred their extraguild prey T. urticae. This study suggested that intraguild prey served as an alternative prey for intraguild predators prolonged survival and ensured the reproduction of intraguild predators during food shortage, ultimately decreasing the need for the continual release of the predators. Full article

Maternal effects can reduce offspring susceptibility to predators by altering resource allocation to young and reproducing larger offspring. While the perception of predation risk can vary according to a prey’s life stage, it is unclear whether maternally experienced intraguild predation (IGP) risk during different life stages influences the maternal effects of predatory insects. We investigated the influence of exposure to intraguild predators (Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)) during the larval and/or adult stages on reproductive decisions and offspring growth in Menochilus sexmaculatus (Fabricius). Independent of the life stage, when M. sexmaculatus females experienced IGP risk, their body weight and fecundity decreased, but the proportion of trophic eggs produced increased. However, egg mass, egg clutch number, and egg clutch size were not influenced by the treatment. Next, when offspring encountered H. axyridis, mothers experiencing IGP risk during the larval and/or adult stages could increase their offspring’s weight. Moreover, offspring in IGP environments reached a similar size as those with no-IGP environments when mothers experienced IGP risk during the larval and/or adult stages. Overall, M. sexmaculatus larval and/or adult exposure to IGP risk had no influence on egg size, but increased offspring body size when faced with H. axyridis. Additionally, mothers experiencing IGP risk during different life stages showed increased production of trophic eggs. Because IGP is frequently observed on M. sexmaculatus and favours relatively larger individuals, different stages of M. sexmaculatus express threat-sensitively to IGP risk; inducing maternal effects can be an adaptive survival strategy to defend against H. axyridis. Full article

The fall armyworm (FAW), Spodoptera frugiperda, has become one of the most important pests on corn in China since it invaded in 2019. Although FAW has not been reported to cause widespread damage to rice plants in China, it has been sporadically found feeding in the field. If FAW infests rice in China, the fitness of other insect pests on rice may be influenced. However, how FAW and other insect pests on rice interact remains unknown. In this study, we found that the infestation of FAW larvae on rice plants prolonged the developmental duration of the brown planthopper (BPH, Nilaparvata lugens (Stål)) eggs and plants damaged by gravid BPH females did not induce defenses that influenced the growth of FAW larvae. Moreover, co-infestation by FAW larvae on rice plants did not influence the attractiveness of volatiles emitted from BPH-infested plants to Anagrus nilaparvatae, an egg parasitoid of rice planthoppers. FAW larvae were able to prey on BPH eggs laid on rice plants and grew faster compared to those larvae that lacked available eggs. Studies revealed that the delay in the development of BPH eggs on FAW-infested plants was probably related to the increase in levels of jasmonoyl-isoleucine, abscisic acid and the defensive compounds in the rice leaf sheaths on which BPH eggs were laid. These findings indicate that, if FAW invades rice plants in China, the population density of BPH may be decreased by intraguild predation and induced plant defenses, whereas the population density of FAW may be increased. Full article

(1) Background: The effects of density and the habitat conditions on the prey vulnerability in the Intraguild Predation (IGP) system were evaluated using the water bug D. rusticus as the top predator. (2) Methods: Using two different density levels (low or high) of the dipteran prey (mosquito and chironomid), the IGP system was set with A. bouvieri as the IG prey. (3) Results: The prey vulnerability was reduced in complex habitat conditions, irrespective of the prey and predator density levels and the prey identity. Correspondingly, the IG prey vulnerability was higher in the low shared prey density and complex habitat. The IG prey consumption by the top predator was higher with the mosquito as shared prey than chironomid as shared prey. Observations on the prey consumption indicated that the consumption of both the chironomid and the mosquito prey dwindled with the time for all combinations of the prey density and the habitat conditions. On a comparative scale, the prey clearance rates were higher for mosquitoes in contrast to the chironomid larvae as shared prey. (4) Conclusions: Apparently, a complex set of interactions involving the habitat conditions, top predator and the prey determines mosquito prey vulnerability against the water bug. Such interactions provide evidence for the coexistence of the mosquito larvae along with multiple predators in the wetland ecosystem. Full article

Intraguild predation (IGP) can have a significant impact on phytoplankton biomass, but its effects on their diversity and assemblage composition are not well understood. In this study, we constructed an IGP model based on the common three-trophic food chain of “fish (or shrimp)–large branchiopods (Daphnia)–phytoplankton”, and investigated the effects of IGP on phytoplankton assemblage composition and diversity in outdoor mesocosms using environmental DNA high-throughput sequencing. Our results indicated that the alpha diversities (number of amplicon sequence variants and Faith’s phylogenetic diversity) of phytoplankton and the relative abundance of Chlorophyceae increased with the addition of Pelteobagrus fulvidraco, while similar trends were found in alpha diversities but with a decrease in the relative abundance of Chlorophyceae in the Exopalaemon modestus treatment. When both predators were added to the community, the strength of collective cascading effects on phytoplankton alpha diversities and assemblage composition were weaker than the sum of the individual predator effects. Network analysis further showed that this IGP effect also decreased the strength of collective cascading effects in reducing the complexity and stability of the phytoplankton assemblages. These findings contribute to a better understanding of the mechanisms underlying the impacts of IGP on lake biodiversity, and provide further knowledge relevant to lake management and conservation. Full article

Disruptive selection arises when extreme phenotypes have a fitness advantage compared to more-intermediate phenotypes. Theory and evidence suggest that intraspecific resource competition is a key driver of disruptive selection. However, while competition can be indirect (exploitative) or direct (interference), the role of interference competition in disruptive selection has not been tested, and most models of disruptive selection assume exploitative competition. We experimentally investigated whether the type of competition affects the outcome of competitive interactions using a system where disruptive selection is common: Mexican spadefoot toads (Spea multiplicata). Spea tadpoles develop into alternative resource-use phenotypes: carnivores, which consume fairy shrimp and other tadpoles, and omnivores, which feed on algae and detritus. Tadpoles intermediate in phenotype have low fitness when competition is intense, as they are outcompeted by the specialized tadpoles. Our experiments revealed that the presence of carnivores significantly decreased foraging behavior in intermediate tadpoles, and that intermediate tadpoles had significantly lower growth rates in interference competition treatments with carnivores but not with omnivores. Interference competition may therefore be important in driving disruptive selection. As carnivore tadpoles are also cannibalistic, the ‘fear’ effect may have a greater impact on intermediate tadpoles than exploitative competition alone, similarly to non-consumptive effects in predator–prey or intraguild relationships. Full article