Daily Prey Consumption and Functional Response of Orius insidiosus: Implications for Biological Control of Scirtothrips dorsalis in Strawberries

Simple Summary

Chilli thrips, Scirtothrips dorsalis Hood, have recently become a major pest of Florida strawberries after its invasion in the US. Biological control is an important measure in the integrated management of this pest. However, biological control of S. dorsalis heavily depends on the release of predatory mites. The predatory insect Orius insidiosus can also be a potential biocontrol agent for S. dorsalis. This study observed the daily prey consumption rate and type of functional response expressed by O. insidiosus with increased prey density. Results showed that O. insidiosus adults consumed more prey than fifth-instar nymphs and showed Type II functional response preying on both adult and immature life stages of S. dorsalis. The results revealed that O. insidiosus has the potential to suppress the population of S. dorsalis.

Abstract

Strawberry is an important specialty crop grown in Florida. Recently, chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), have become a significant threat to Florida strawberry production. Pesticide applications are not always recommended because of the development of insecticidal resistance. Biological control can be a viable control option for this pest. However, the management of S. dorsalis using predatory bug Orius insidiosus Say (Hemiptera: Anthocoridae) has never been explored in strawberries. Therefore, this study’s aim was to evaluate the predation efficacy of O. insidiosus through daily consumption rate and the functional response while preying on S. dorsalis. The results suggest that adult O. insidiosus has a significantly higher daily consumption rate than fifth-instar nymphs when feeding on both life stages of S. dorsalis. A Type II functional response was expressed by O. insidiosus when feeding on larval and adult S. dorsalis, indicating that the predation rate can increase with the prey density before it reaches a saturation point. The attack rates (a) and prey handling time (T_h) were also computed on second-instar larvae and adult S. dorsalis, respectively. The results indicate that O. insidiosus can be used as an augmentation biocontrol agent for S. dorsalis management in strawberries.

1. Introduction

Strawberry Fragaria × ananassa Duchesne (Rosales: Rosaceae) is an important horticultural crop in Florida, U.S.A., cultivated on over 5200 hectares and generating a revenue of about USD 511 million annually [1]. Various arthropod pests, including tarnished plant bug Lygus lineolaris (Pallisot de Beauvois) (Hemiptera: Miridae), two-spotted spider mite Tetranychus urticae (Koch) (Acari: Tetranychidae), and cyclamen mite Phytonemus pallidus (Banks) (Acari: Tarsonemidae), infest open-field strawberries throughout the growing season in Florida [2]. Lately, the invasive chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), has become a significant pest of Florida strawberries after its introduction from Southeast Asia in 2005 [3]. Scirtothrips dorsalis infestation on strawberry plants produces dark malformed leaves and bronzed, cracked fruits. The management of S. dorsalis is mainly dependent on insecticide applications; however, excessive insecticide use can result in resistant S. dorsalis populations [4] and harm the non-target organisms [5]. Biological control may provide an alternative or complementary strategy to insecticide application for managing S. dorsalis. Biological control can be defined as the use of living organisms to reduce the pest population, making it less prevalent than it would be naturally [6].

Orius insidiosus Say (Hemiptera: Anthocoridae), commonly known as the minute pirate bug, is a generalist predator [7] abundant in many parts of the United States that feeds on many important insect pests. Orius spp. are commercially available and can be used in augmentation biocontrol in greenhouses or open-field agriculture to manage different thrips species [8]. For example, a high density Orius spp. was found to control the population of Thrips palmi Karny (Thysanoptera: Thripidae) in greenhouse eggplants in Japan [9]. The predation efficacy of Orius spp. was observed against Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) and Thrips tabaci Lindeman (Thysanoptera: Thripidae) on sweet pepper in the greenhouse [8]. Orius insidious was also an effective predator of F. occidentalis on chilli pepper in the field [10].

Orius laevigatus (Fieber) (Hemiptera: Anthocoridae), native to Europe, was efficient in controlling F. occidentalis in strawberries [11] and in that study, the number of F. occidentalis per strawberry flower reduced when the predators were released compared to the control cages without the predators. However, very few studies have evaluated Orius spp. for managing S. dorsalis. Orius laevigatus and Amblyseius swirskii Athias-Henriot (Arachnida: Phytoseiidae) effectively controlled S. dorsalis on chilli pepper in Sri Lanka [12]. Another study found that O. insidious in association with A. swirskii effectively reduced S. dorsalis population and O. insidious was more efficient in controlling adult thrips than A. swirskii [13].

Many reports have shown the efficiency of anthocorid bugs feeding on soft-bodied insects, including thrips [14]. However, pest control by predators depends on many factors, including the predator’s biological and behavioral traits [15]. One important method to evaluate a biological control agent’s efficacy is to ascertain its response to the changes in prey densities or understand its functional response [15].

The functional response of a predator can be defined as a relationship between prey density and prey consumption [16]. It is commonly used as a primary indicator of the ability of a candidate biocontrol agent to suppress the pest population below the threshold level [17,18]. Three types of functional responses were defined by Holling 1959 [19]. In Type I, predators demonstrate a linear increase in the consumption rate with an increase in prey density; in Type II, predators gradually decrease the prey consumption as the prey density increases; and in Type III, predators demonstrate a rise in consumption rate which follows a sigmoidal response shape. Functional response helps one to understand two crucial parameters of predators, i.e., prey handling time and searching ability [20].

Previous studies using Orius laevigatus and Orius majusculus (Reuter) (Hemiptera: Anthocoridae) showed a Type II functional response when preying on two aphid species, Aphid gossypii Glover and Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) [21]. In another study, O. laevigatus and O. majusculus were tested for functional responses on whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) pupae (fourth-instar nymphs) and F. occidentalis second-instar larvae in greenhouse vegetables. This study also found a Type II functional response by both Orius spp. [22]. A previous study with Orius sauteri (Hemiptera: Anthocoridae) (Poppius) showed a Type II functional response towards Thrips palmi [23].

In Florida strawberries, the main biological control agents used for the management of S. dorsalis and T. urticae are predatory mites. The potential of Orius spp., which are known thrips predators, to control S. dorsalis in strawberries has not been studied before. Therefore, the objective of the study was to (1) determine the rate of daily prey consumption by adult and fifth-instar nymphs of predatory insect Orius insidiosus and (2) determine the type of functional response expressed by O. insidiosus with increased prey density. As both larvae and adults of S. dorsalis are damaging life stages to strawberry plants, both life stages were tested in this experiment. On the other hand, all life stages of O. insidiosus are predatory, which is why both the fifth-instar nymph and adults were tested for their daily prey consumption rate.

2. Materials and Methods

Laboratory colony of S. dorsalis: Upland cotton plants, Gossypium hirsutum L. (Malvaceae), were grown from seed in pots (10.2 cm × 8.9 cm, Greenhouse Megastore, Danville, IL, USA) with soil (BWI Pro-Mix 2.8 cf; BWI Companies, Nash, TX, USA) in a growth room at the Gulf Coast Research and Education Center (GCREC) (27.7604, −82.2275), for maintaining an S. dorsalis colony. The cotton plants infested with S. dorsalis were kept inside cages (Bug Dorm, BioQuip Products Inc. Compton, CA, USA) at 25 ± 5 °C and 60 ± 5% RH in a 16L:8D hour photophase. New cotton plants were introduced inside the previously infested cages every two weeks. All plants were watered as needed every alternate day and fertilized (J R Peter’s Jacks General All-Purpose Fertilizer, Allentown, PA, USA) once in two weeks.

Strawberry plant husbandry: Bare-root transplants of the strawberry cultivar “Florida Brilliance” (US Patent PP 30,564) [24] were obtained from a commercial nursery (Crown Nursery LLC, Red Bluff, CA, USA). The transplants were planted in pots of the same size as described in the previous section and maintained accordingly. Plants were kept inside a greenhouse at GCREC with a temperature of 25 ± 5 °C and 75 ± 5% relative humidity (HOBO U23 Prov2; Onset Computer Corporation, Bourne, MA, USA) and a natural photoperiod. After almost three weeks, when the plants had at least five full-grown trifoliates, the leaves were used in the experiment.

Rate of daily prey consumption: All bioassays were conducted in the Strawberry and Small Fruit Entomology Lab at Gulf Coast Research and Education Center (27.712490°, −82.302322°). Each experimental unit was a polypropylene Petri dish with a 5 cm diameter (Fisherbrand, Suwanee, GA, USA). Orius insidiosus were purchased from commercial sources (BioBee Ltd., Salisbury, MD, USA and Crop Defenders Ltd., Plymouth, MI, USA). All the predators used in the study were starved for 24 h upon arrival before the experiment and provided with water only. One young strawberry leaf was fitted inside the Petri dish. A small piece of moist filter paper was provided as a moisture source (5.5 cm diameter Whatman qualitative filter paper, Sigma-Aldrich^®, Saint Louis, MO, USA). Ten adult S. dorsalis were collected from the existing colony by aspiration and released in the Petri dish. One individual O. insidiosus adult was released as a predator in the Petri dish. A similar experimental arena was prepared for the fifth-instar nymph of O. insidiosus, with ten S. dorsalis provided as prey. Two life stages, i.e., second-instar larvae and adults of S. dorsalis, were tested separately in these arenas as prey for O. insidiosus. After releasing both prey and predator, the Petri dishes were sealed with Parafilm™ (Fisher Scientific, Hampton, NH, USA) and labeled with the date. The Petri dishes were maintained at 25 °C and 65% RH in a 16L: 8D photoperiod. Petri dishes were examined under a stereomicroscope (Stemi 508, Carl Zeiss, Germany) at 40× magnification after 24 h and the number of prey consumed was recorded. Each experiment was repeated three times with ten replications per treatment.

Functional Response: The experimental arena was a 5 cm polypropylene Petri dish (Fisherband, Suwanee, GA, USA). Each Petri dish had a strawberry leaf (Florida Brilliance) and a moist filter paper (5.5 cm diameter Whatman qualitative filter paper, Sigma-Aldrich^®, MO, USA) as a moisture source. Prey densities of 5, 10, and 20 S. dorsalis adult and second-instar larvae were used in the study. Adult Orius insidiosus were starved for 24 h before the experiment and provided with water only. One adult predator was released into the arena with the prey. After 24 h, the prey consumption was evaluated under a stereomicroscope (Stemi 508, Carl Zeiss, Germany) at 40× magnification and the mortality data were recorded. The experiment was performed at 25 ± 1 °C and 65 ± 5% RH in a 16L: 8D photoperiod. The experiment was conducted with ten replicates for each prey density and repeated three times.

Data analysis: The difference between prey consumption by adults and 5th-instar nymphs of O. insidiosus was determined using a generalized linear mixed model (Proc Glimmix) in SAS OnDemand for Academics web platform (SAS Ins. Cary, NC, USA). Mean separation was performed using Tukey’s HSD at α = 0.05.

Functional response was determined by the number of prey consumed at different prey densities. Data analysis was performed in two steps. In the first step, logistic regression analysis was performed to determine the type of functional response expressed by O. insidiosus. The linear coefficient was determined by logistic regression of the proportion of the consumed (N_a/N₀) prey as a function of prey offered [25].

$${\displaystyle \frac{{\mathrm{N}}_{\mathrm{a}}}{{\mathrm{N}}_0}}={\displaystyle \frac{\exp ({\mathrm{P}}_0+{\mathrm{P}}_1{\mathrm{N}}_0^1+{\mathrm{P}}_2{\mathrm{N}}_0^2+{\mathrm{P}}_3{\mathrm{N}}_0^3)}{1+\exp ({\mathrm{P}}_0+{\mathrm{P}}_1{\mathrm{N}}_0^1+{\mathrm{P}}_2{\mathrm{N}}_0^2+{\mathrm{P}}_3{\mathrm{N}}_0^3)}}$$

(1)

where N_a = prey consumed, N₀ = initial prey offered, P₀, P₁, P₂, and P₃ are the intercept, linear, quadratic, and cubic co-efficients, respectively, and N_a/N₀ is the probability of prey consumed. These parameters were calculated by Proc CATMOD in SAS OnDemand for Academics web platform (SAS Ins. Cary, NC, USA). According to Juliano, [26] when P₁ < 0 and P₂ > 0, the proportion of consumed prey decreased gradually as the initial number of prey increased. This phenomenon follows a Type II functional response. The maximum likelihood estimates show how the independent variable, which was the different initial prey counts, influences the likelihood of different predation outcomes. This study divided the initial prey count into three levels, 5 as low, 10 as medium, and 20 as high, and the outcome may represent different predator behaviors: low, medium, and high predation activity. In our study, the model considered the medium initial prey density (10 S. dorsalis per O. insidiosus) as the reference level.

In the second step of the analysis, after the type of functional relationship had been determined, the Holling disc equation (Equation (2)) was used to understand the parameters of predator attack rate or instantaneous searching rate (a) and handling time (h). A non-linear least square regression was performed by Proc NLIN in SAS OnDemand for Academics web platform to estimate these parameters.

$${\mathrm{N}}_{\mathrm{a}}={\displaystyle \frac{\mathrm{aT}{\mathrm{N}}_0}{1+{\mathrm{T}}_{\mathrm{h}}{\mathrm{N}}_0}}$$

(2)

where N_a = number of prey consumed; N₀ = initial number of prey; a = searching efficiency or attack rate; T = total time available for the predator exposure, which was 24 h in our experiment; and T_h = handling time per prey. The attack rate (a) and handling time (T_h) were analyzed after the determination of Type II functional response following the Holling disc equation [19].

3. Results

3.1. Daily Consumption Rate of O. insidiosus on S. dorsalis

In both experimental settings, adult O. insidiosus consumed a significantly higher number of prey than fifth-instar nymphs. In the experimental arena where the adult S. dorsalis was offered as prey, the adult O. insidiosus consumed a significantly higher number of prey compared to the fifth-instar nymphs (F = 77.2, df = 1,56, p < 0.0001) (Figure 1). A similar result was obtained when the second-instar larvae of S. dorsalis were offered as prey (F = 82.5, df = 1,56, p < 0.0001) (Figure 2).

3.2. Functional Response of O. insidiosus on S. dorsalis (Second-Instar Larvae)

The intercept (P₀) represents the baseline log odds when all other variables were at their reference level, which is the medium initial prey category in this case. When the second-instar larvae were offered as prey, the first possible outcome was −1.22003 (p < 0.0001) (

Table 1. Maximum likelihood estimates from logistic regression of the proportion of the second-instar larva of S. dorsalis eaten by adult O. insidiosus.

Parameter		Co-Efficient	Function Number	Estimate	STD Err	Chi-Square	Pr > Chi-Square
Intercept		P0 Intercept	1	−1.2203	0.1357	80.87	<0.0001
		P0 Intercept	2	0.1951	0.0918	4.52	0.033
Initial_prey_cat	High	P1 Linear	1	−0.2338	0.1601	2.13	0.1441
	High	P1 Linear	2	−0.2158	0.1057	4.17	0.0412
	Low	P2 Quadratic	1	0.6607	0.2267	8.53	0.0035
	Low	P2 Quadratic	2	0.7211	0.1584	20.73	<0.0001

), suggesting that the baseline likelihood of this outcome was low before considering changes in prey availability, whereas possible outcome 2 was 0.1951 (p = 0.033). This was positive and statistically significant above zero, indicating a higher baseline likelihood of this outcome relative to the reference category (Table 1). This result suggests that predators will be more likely to engage in predation activity when the initial prey is at the reference level (10 S. dorsalis per O. insidiosus).

The first possible outcome of the linear co-efficient (P₁) showed that certain predation outcomes decreased as the estimate was negative and not significant (−0.2338 p = 0.1441). This result indicated that high initial prey density had very little effect on predator behavior (Table 1). In comparison, possible outcome 2, regarding the high initial prey density, showed an estimate of −0.2158 (p = 0.0412). This result indicated that the odds of the outcome were significantly low, relative to the reference category. This suggests that O. insidiosus might be less likely to consume a higher amount of prey when initial prey density is high.

The two possible outcomes of the quadratic co-efficient (P₂) were 0.6607 (p = 0.0035) and 0.7211 (p = <0.001) These two estimates were positive and significant, which indicates the increase in the log odds of different biological outcomes such as partial or complete predation of available prey compared to the reference category. This suggests that when the initial prey S. dorsalis numbers were low, the predator was more likely to engage in predation.

3.3. Functional Response of O. insidiosus on S. dorsalis (Adults)

The possible outcomes of intercept (P₀) were 0.8500 (p < 0.0001) and 0.3973 (p = 0.0195), respectively, which were positive and significantly above zero. These results indicate that O. insidiosus would show some predacious activity without considering the initial prey density when adult S. dorsalis is offered as prey (

Table 2. Maximum likelihood estimates from logistic regression of the proportion of the adult S. dorsalis eaten by adult O. insidiosus.

Parameter			Function Number	Estimate	STD Err	Chi-Square	Pr > ChiSq
Intercept		P0 Intercept	1	0.8500	0.1597	28.34	<0.0001
		P0 Intercept	2	0.3973	0.1701	5.46	0.0195
Initial_prey_cat	High	P1 Linear	1	−0.4989	0.1732	8.30	0.004
	High	P1 Linear	2	−2.3432	0.2238	109.60	<0.0001
	Low	P2 Quadratic	1	0.6698	0.2890	5.37	0.0205
	Low	P2 Quadratic	2	1.9053	0.2852	44.64	<0.0001

).

The linear co-efficient (P₁) showed both possible outcomes as negative and statistically significant: −0.4989 (p = 0.004) and −2.3432 (p = <0.0001) (Table 2). These values indicated that the predator O. insidiosus was less likely to engage in predation activity when the initial prey density was high.

The quadratic co-efficient (P₂) showed both of the possible outcomes as positive and significant, 0.6698 (p = 0.0205) and 1.9053, (p < 0.0001), respectively. These positive and significant estimates indicated an increase in the log odds of the predation activity, suggesting that when prey availability is low, the predator will likely acquire more prey.

In summary, the negative values in the high initial prey density in both cases of second-instar larvae and adult S. dorsalis indicate that O. insidiosus was less likely to exploit all of the prey. However, when the initial prey was low, the predator was more likely to maximize the predation rate. This suggests a Type II functional response where predation activity increases rapidly at a low prey density and decreases towards a higher initial prey density.

The attack rates of O. insidiosus on the second-instar larvae and adult S. dorsalis were 0.0342 ± 0.0018 h⁻¹ and 0.0335 ± 0.0042 h⁻¹ per unit of prey density, respectively. The prey handling time was 0.01 ± 0.00 h and 0.8135 ± 0.2419 h for second-instar larvae and adult thrips, respectively (

Table 3. Mean ± SE of attack rate (a) and handling ability (T_h) of O. insidiosus on second-instar larvae and S. dorsalis adults.

Prey Stage	Parameters	Estimate ± SE	Asymptomatic 95% CL		R2
			Lower	Upper
Second-instar larvae	a	0.0342 ± 0.0018	0.0306	0.0379	0.735
	Th	0.01 ± 0.00	0.011	0.01
S. dorsalis adult	a	0.0335 ± 0.004	0.0248	0.0423	0.789
	Th	0.8135 ± 0.2419	0.3328	1.2941

).

4. Discussion

4.1. Daily Prey Consumption

Orius insidiosus adults demonstrated higher prey consumption than the fifth-instar nymphs when both adult and second-instar larvae of S. dorsalis were provided as prey. This result could be due to their better maneuverability than the O. insidiosus nymphal stages [26]. Predators often prefer to prey on insects with less mobility, which could explain the higher predation rate on second-instar larvae of S. dorsalis. Another study found that Orius laevigatus and Orius majusculus were feeding more on sedentary leaf-inhabiting thrips species Echinothrips americanus (Thripidae: Thysanoptera) than mobile thrips like F. occidentalis [27]. A similar result was found by Isenhour and Yeargan [28] where the adult O. insidiosus killed more soybean thrips, Sericothrips variabilis (Beach), compared to O. insidiosus nymphal instars. A lower predation rate by the juvenile stage of a predator could be due to their smaller body size, slower movement, and long prey handling time [29].

4.2. Functional Response of O. insidiosus

The determination of the functional response of any biocontrol agent will advance our understanding of their potency in the regulation of pest population [30]. Previous studies have indicated that most arthropod predators exhibit a Type II functional response [31]. Similarly, our results indicated Type II functional response by O. insidiosus to both life stages of S. dorsalis (Table 1 and Table 2).

Other Orius spp. have previously shown Type II functional responses against various pests. For example, Orius nijer Wolff (Hemiptera: Anthocoridae) and Orius minutus L. (Hemiptera: Anthocoridae) have shown Type II functional responses when Tetranychus urticae adults and second-instar larvae of onion thrips, Thrips tabaci Lindeman, were offered as prey [18]. Orius sauteri (Poppius) also showed a Type II functional response when fed on Megalurothrips usiatus (Bagnall) (Thysanoptera: Thripidae) [32]. Orius albidipennis (Reuter) (Hemiptera: Anthocoridae) exhibited a Type II functional response when preying on Megalurothrips sjostedji Trybom [33]. Another important predator that showed a Type II functional response was the Asian ladybird beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) when feeding on various species of aphids [34].

Predators showing low handling time and high attack rates are believed to be more efficient biological control agents [18]. However, in our study, the attack rate by O. insidiosus was low, observed as 0.0342 ± 0.0018 and 0.0335 ± 0.004 on second-instar larvae and adults of S. dorsalis, respectively (Table 3). As discussed before, the attack rate of the predator can be restricted by handling time [30]. Various thrips species often show anti-predatory behavior, including waging of the abdomen and secretion of anal fluids [35,36] which could have negatively impacted the handling time of the predator. However, in the field, predators can face limitations due to searching area and time [30,37,38]. Handling time refers to a predator’s time to overpower, process, and consume the prey [19]. Low handling implies that the predator can quickly process and consume the prey faster, ultimately increasing the feeding rate. In the case of Type II functional response, low handling time can lead to a higher predation rate [39] because the predator is less constrained with time, allowing it to consume more prey before reaching saturation. From the result of our study, we can say that O. insidiosus will consume prey relatively quickly when the prey density is low. However, when prey density increases, predation becomes limited because of handling time. The predators that show Type II functional response can be used in inundative biological control to reduce the pest population [40].

Functional response is a vital tool in understanding predators’ efficacy, but it cannot be the only measure of the success or failure of a biological control agent. Other biotic and abiotic factors such as host patchiness, intrinsic growth rates, predation and competition, other environmental factors and the ability to survive on alternate food sources, can also significantly affect the adeptness of a predator in managing a pest population [41,42]. Functional response studies performed in laboratory conditions may lack the ability to determine predation characteristics in field conditions [43]. Previous studies have found differences in functional response in the predatory stink bug Podisus maculiventris (Say) (Hemiptera: Pentatomidae) in laboratory and field conditions [44]. Some reasons for this discrepancy could be because of the use of a small study arena in the laboratory which may not be typical for the searching ability of the predator and the spatial complexity of an actual field [45,46,47]. Lastly, plant characteristics such as leaf hairs or trichomes can also influence the predation efficacy of a predator [48,49].

In the field, dispersal ability, prey searching potential, and the presence of other prey species can influence the predation efficacy of any predator. Due to the ability to utilize alternate food sources such as pollen, the dispersal ability of O. insidiosus can be influenced in the field depending on the presence or absence of flowers. A higher dispersal rate of adult O. insidiosus females was found in the strawberry flowers without pollen, and the least dispersal was observed in the flowers with pollen. The flowers with the main prey F. occidentalis result in the intermediate dispersal rate [50]. Apart from dispersal, foraging behavior is another important factor for predatory insects because it directly impacts the predator’s ability to locate prey and reduce the pest population. Orius insidiosus was found to be responsive to the non-volatile cue released by prey species and involved in intensive foraging behavior, with more turns in the foraging area and higher immobile time [51]. In the field, when multiple thrips species were present, O. insidiosus killed more F. occidentalis than Frankliniella bispinosa (Morgan) (Thysanoptera: Thripidae), because F. bispinosa was more mobile and smaller in size than F. occidentalis [52]. This can result in a change in the functional response of a predator from Type II to Type III [53].

This study helps to understand the daily predation rate and interaction of Orius insidiosus with S. dorsalis in the control environment with increased prey density. Considering that Orius spp. had many previous reports of successfully controlling other thrips species in open fields and in the greenhouse, this study may be the first step towards its evaluation as a potential biological control agent against S. dorsalis in strawberries. The range of prey density tested in this study may be expanded in future studies to test population densities above 20 S. dorsalis per strawberry leaf and per O. insidiosus. However, in the current study, this range was selected, keeping in mind the action threshold of S. dorsalis which typically ranges from 2 to 10 thrips per plant tissue type depending on the plant host [54,55]. This type of experiment with even higher prey densities presents a logistical challenge with handling highly mobile prey such as S. dorsalis.

5. Conclusions

Our study indicates that adult Orius insidiosus demonstrates a Type II functional response to both prey life stages, i.e., adult and second-instar larvae of S. dorsalis. In addition, adult O. insidiosus consumed a significantly higher number of prey than the fifth-instar nymphs in 24 h. However, further field studies are needed to understand the predator responses in the field, including foraging behavior, dispersal activity among strawberry plants, and population dynamics in the field. This study highlights the potential of O. insidiosus as a biological control agent for S. dorsalis in strawberries, offering a sustainable alternative to chemical insecticides.