Preference and prey switching in a generalist predator attacking local and invasive alien pests

Dietary experience alters predatory behavior of two ladybird species on tomato potato psyllid

The tomato potato psyllid, Bactericera cockerelli, is an invasive pest in Australia, which can cause severe economic loss in the production of Solanaceous crops. As an invasive pest, B. cockerelli may also modify biotic interactions in Australian agricultural and native ecosystems. Resident generalist predators in an area may have the ability to utilize invasive pest species as prey but this will depend on their specific predatory behavior. The extent to which generalist predators learn from their previous dietary experience (i.e., whether they have used a particular species as prey before) and how this impacts subsequent prey choice will influence predator and prey population dynamics after invasion. In this study, one nonnative resident ladybird, Hippodamia variegata, and one native ladybird, Coccinella transversalis, were investigated. Dietary experience with B. cockerelli as a prey species significantly increased preference for the psyllid in a short term (6 h) Petri dish study where a choice of prey was given. Greater suppression of B. cockerelli populations by experienced ladybirds was also observed on glasshouse grown tomato plants. This was presumably due to altered prey recognition by experience. The result of this study suggest the potential to improve the impact of biological control agents on invasive pests by providing early life experience consuming the target species. It may prove valuable for developing improved augmentative release strategies for ladybirds to manage specific insect pest species.

Presence of nontarget prey, Tetranychus truncatus, affected the predation by Neoseiulus bicaudus on Tetranychus turkestani

Neoseiulus bicaudus (Wainstein) (Acari: Phytoseiidae) is a generalist predatory mite that consumes several pest species, including Tetranychus turkestani (Ugarov et Nikolskii) (Acari: Tetranychidae) in the Xinjiang Uygur Autonomous Region. The release numbers of predatory mites are based on the populations of target pests and their ability to control them. Populations of T. turkestani and T. truncatus Ehara (Acari: Tetranychidae) often coexist and damage many crops. To determine whether the presence of the non-target prey T. truncatus affects the ability of N. bicaudus to control the target prey T. turkestani. The study evaluated the predation rate and functional response of N. bicaudus to 4 stages of T. turkestani in the presence of T. truncatus. The consumption of T. turkestani by N. bicaudus gradually decreased as the proportion of T. truncatus increased. The functional response of N. bicaudus to T. turkestani was not changed when T. truncatus was presented, which was consistent with a type II response. The attack rate of N. bicaudus on the egg, larva, and nymph of T. turkestani was significantly decreased and the handling time of N. bicaudus on T. turkestani was significantly extended when T. truncatus was presented. The preference index showed that the preference of N. bicaudus for eggs and female adults of T. turkestani decreased with increasing density of T. turkestani in the same proportion as T. truncatus. The presence of T. truncatus can negatively affect the predation of T. turkestani by N. bicaudus. We suggest that the number of N. bicaudus released to control T. turkestani should be increased when T. truncatus coexist.

Direct and indirect effects of banker plants on population establishment of Harmonia axyridis and aphid control on pepper crop

Banker plant systems increase biological pest control by supporting populations of natural enemies, i.e., using non-pest arthropod species as alternative prey. However, the presence of alternative prey does not always result in improved control of the target pest species owing to the complexity of biotic interactions. To increase the effectiveness of banker plants in IPM programs, a fine understanding of the indirect interactions between target aphid and alternative prey mediated by biocontrol agents is necessary. In this study, we first established a banker plant system, banker plant (Vicia faba)-alternative prey (Megoura japonica)-predator (Harmonia axyridis), to control the target pest (Myzus persicae) on pepper. We found that M. japonica strongly preferred faba bean as a host plant and posed no risk to Solanaceous crops. Harmonia axyridis adults had no significant predation preference for the alternative prey. In the short term, the interaction direction of the two aphid species depended on the relative initial density and the timescale. Harmonia axyridis showed a stronger negative effect on M. persicae than that on M. japonica. In the long term, the presence of alternative prey, M. japonica, enhanced the control effect of H. axyridis to M. persicae with initial density of 100-500 aphids per plant. The presence of the alternative prey could proliferate the population of H. axyridis, with from 0.2- to 2.1-fold increase of H. axyridis eggs. Overall, we put forward a strategy for setting the initial density of alternative prey of the banker plant system to target the high and low density of aphids, which highlighted the importance of indirect interactions in designing a proper banker plant system.

Sesame as an Alternative Host Plant to Establish and Retain Predatory Mirids in Open-Field Tomatoes

The silverleaf whitefly (Bemisia tabaci) and the South America tomato pinworm (Tuta absoluta) are two of the most destructive pests of tomato. Open-field tomato production frequently relies on chemical treatments, which has been shown to lead to pesticide resistance. The integration of biological control using predatory mirid bugs is an effective alternative method for managing these pests. However, methods to establish and maintain populations of zoophytophagous mirids are not adequately described. We explored the potential use of two mirids naturally occurring in Florida, Nesidiocoris tenuis and Macrolophus praeclarus. We conducted 6 field experiments over 4 consecutive years to develop a strategy to maintain the mirids. Pre-plant inoculation of tomato plants did not lead to their establishment, likely due to the low prevalence of prey. We explored the use of sesame (Sesamum indicum) to retain the mirids. Intercropping sesame maintained the populations of N. tenuis throughout the duration of the crop. Macrolophus praeclarus never established in any of the open-field experiments. Nesidiocoris tenuis damage was minimal (<1 necrotic ring/plant) and mirid damage was reduced in the presence of sesame. Our results show that intercropping sesame may provide a means to utilize mirids to manage B. tabaci, an established pest, and provide options to tomato growers should T. absoluta invade USA.

Predation increases multiple components of microbial diversity in activated sludge communities

Protozoan predators form an essential component of activated sludge communities that is tightly linked to wastewater treatment efficiency. Nonetheless, very little is known how protozoan predation is channelled via bacterial communities to affect ecosystem functioning. Therefore, we experimentally manipulated protozoan predation pressure in activated-sludge communities to determine its impacts on microbial diversity, composition and putative functionality. Different components of bacterial diversity such as taxa richness, evenness, genetic diversity and beta diversity all responded strongly and positively to high protozoan predation pressure. These responses were non-linear and levelled off at higher levels of predation pressure, supporting predictions of hump-shaped relationships between predation pressure and prey diversity. In contrast to predation intensity, the impact of predator diversity had both positive (taxa richness) and negative (evenness and phylogenetic distinctiveness) effects on bacterial diversity. Furthermore, predation shaped the structure of bacterial communities. Reduction in top-down control negatively affected the majority of taxa that are generally associated with increased treatment efficiency, compromising particularly the potential for nitrogen removal. Consequently, our findings highlight responses of bacterial diversity and community composition as two distinct mechanisms linking protozoan predation with ecosystem functioning in activated sludge communities.

Does the dose make the poison? Neurotoxic insecticides impair predator orientation and reproduction even at low concentrations

BACKGROUND

Pesticides can be noxious to non-target beneficial arthropods and their negative effects have been recently recognized even at low doses. The predator Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) plays an important role in controlling insect pests in solanaceous crops, but its concurrent herbivory often poses relevant concerns for tomato production. Although insecticide side effects on N. tenuis have been previously studied, little is known on the potential implications of neurotoxic chemicals at low concentrations. We assessed the baseline toxicity of three neurotoxic insecticides (lambda-cyhalothrin, spinosad and chlorpyrifos) on N. tenuis by topical contact exposure. The behavioral and reproduction capacity of the predator was then investigated upon exposure to three estimated low-lethal concentrations (LC₁ , LC₁₀ and LC₃₀ ).

RESULTS

Predator survival varied among insecticides and concentrations, with LC₃₀ /label rate ratios ranging from 8.45% to 65.40% for spinosad and lambda-cyhalothrin, respectively. All insecticides reduced the fertility of N. tenuis females at all estimated low-lethal concentrations. Chlorpyrifos seriously compromised predator orientation towards a host plant even at LC₁ , while the same effect was observed for lambda-cyhalothrin and spinosad solely at LC₃₀ . Lambda-cyhalothrin (at all concentrations) and chlorpyrifos (at LC₁₀ and LC₃₀ ) also affected the time taken by N. tenuis females to make a choice.

CONCLUSION

The results indicate that all three insecticides can be detrimental to N. tenuis and should be avoided when presence of the predator is desirable. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Combination of generalist predators, Nesidiocoris tenuis and Macrolophus pygmaeus, with a companion plant, Sesamum indicum: What benefit for biological control of Tuta absoluta?

Tuta absoluta is one of the most damaging pests of tomato crops worldwide. Damage due to larvae may cause up to 100% loss of tomato production. Use of natural enemies to control the pest, notably predatory mirids such as Nesidiocoris tenuis and Macrolophus pygmaeus, is increasingly being promoted. However, considering the potential damage caused to tomatoes by these omnivorous predators in the absence of T. absoluta, an alternative solution could be required to reduce tomato damage and improve the predators' performance. The use of companion plants can be an innovative solution to cope with these issues. The present study aimed to determine the influence of companion plants and alternative preys on the predators' performance in controlling T. absoluta and protecting tomato plants. We evaluated the effect of predators (alone or combined) and a companion plant (sesame (Sesamum indicum)) on T. absoluta egg predation and crop damage caused by N. tenuis. The influence of an alternative prey (Ephestia kuehniella eggs) on the spatial distribution of predators was also evaluated by caging them in the prey presence or absence, either on tomato or sesame plants or on both. We found that the presence of sesame did not reduce the efficacy of N. tenuis or M. pygmaeus in consuming T. absoluta eggs; hatched egg proportion decreased when N. tenuis, M. pygmaeus, or both predators were present. More specifically, this proportion was more strongly reduced when both predators were combined. Sesame presence also reduced necrotic rings caused by N. tenuis on tomato plants. Nesidiocoris tenuis preferred sesame over tomato plants (except when food was provided only on the tomato plant) and the upper part of the plants, whereas M. pygmaeus preferred tomato to sesame plants (except when food was provided only on the sesame plant) and had no preference for a plant part. Combination of predators N. tenuis and M. pygmaeus allows for better coverage of cultivated plants in terms of occupation of different plant parts and better regulation of T. absoluta populations. Sesamum indicum is a potential companion plant that can be used to significantly reduce N. tenuis damage to tomatoes.

Effect of Drosophila suzukii on Blueberry VOCs: Chemical Cues for a Pupal Parasitoid, Trichopria anastrephae

Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical landscape may be altered by the invasion of exotic insect species. The spotted-wing drosophila (SWD), Drosophila suzukii (Diptera: Drosophilidae), is a highly polyphagous fruit pest native to eastern Asia and recently arrived in South America. Our study aimed to characterize the effect of SWD attack on the volatile organic compounds (VOCs) of blueberries, a common host fruit, and to correlate these odor changes with the olfactory-mediated behavioral response of resident populations of Trichopria anastrephae parasitoids, here reported for the first time in Uruguay. Using fruit VOC chemical characterization followed by multivariate analyses of the odor blends of blueberries attacked by SWD, we showed that the development of SWD immature stages inside the fruit generates a different odor profile to that from control fruits (physically damaged and free of damage). These differences can be explained by the diversity, frequency, and amounts of fruit VOCs. The behavioral response of T. anastrephae in Y-tube bioassays showed that female wasps were significantly attracted to volatiles from SWD-attacked blueberries when tested against both clean air and undamaged blueberries. Therefore, T. anastrephae females can use chemical cues from SWD-infested fruits, which may lead to a successful location of their insect host. Since resident parasitoids are able to locate this novel potential host, biological control programs using local populations may be plausible as a strategy for control of SWD.

Predators of the giant pine scale, Marchalina hellenica (Gennadius 1883; Hemiptera: Marchalinidae), out of its natural range in Turkey

Marchalina hellenica is a sap sucking scale insect endemic to the Aegean basin and it has been introduced to several regions in Greece and Turkey to increase pine honey production. It is also considered as a pest since heavy infestation may leave the host trees vulnerable to secondary pests. An understanding of its natural predators would facilitate planning biocontrol programs. Although there are several studies reporting the predators of M. hellenica in its native range, there is no study identifying those in its introduced range. We aimed to determine predators of M. hellenica in Burdur, one of its introduced sites in Turkey. We carried out sampling through regular visits in an M. hellenica-infested locality nearby Burdur Lake. Through field and laboratory observations, we identified 19 species predating upon M. hellenica. Comparing predators reported in previous studies in its native range and those we found in the present study showed that 12 of the species that we found are new reports for the species predating upon M. hellenica. The highest number of predator individuals belonged to the monophagous Neoleucopis kartliana. Myrrha octodecimguttata, Chilocorus bipustulatus and Harmonia quadripunctata were also the most frequently observed predators.

Using ensemble modeling to predict the impacts of assisted migration on recipient ecosystems

Assisted migration is a controversial conservation measure that aims to protect threatened species by moving part of their population outside its natural range. Although this could save species from extinction, it also introduces a range of risks. The magnitude of the threat to recipient ecosystems has not been investigated quantitatively, despite being the most common criticism leveled at the action. We used an ensemble modeling framework to estimate the risks of assisted migration to existing species within ecosystems. With this approach, we calculated the consequences of an assisted migration project across a very large combination of translocated species and recipient ecosystems. We predicted the probability of a successful assisted migration and the number of local extinctions would result from establishment of the translocated species. Using an ensemble of 1.5×106 simulated 15-species recipient ecosystems, we estimated that translocated species will successfully establish in 83% of cases if introduced to stable, high-quality habitats. However, assisted migration projects were estimated to cause an average of 0.6 extinctions and 5% of successful translocations triggered 4 or more local extinctions. Quantifying the impacts to species within recipient ecosystems is critical to help managers weigh the benefits and negative consequences of assisted migration.

Detrimental sublethal effects hamper the effective use of natural and chemical pesticides in combination with a key natural enemy of Bemisia tabaci on tomato

BACKGROUND

Bemisia tabaci (Hemiptera: Aleyrodidae) represents one of the greatest threats to agricultural crops. Chemical control is the primary tool used in integrated pest management (IPM) programs. However, release of the predator Nesidiocoris tenuis (Hemiptera: Miridae) on tomato plants is a highly recommended control tactic. The objective of this study was to evaluate the efficacy of a commercial borax plus citrus oil (BCO) product against B. tabaci in the presence and absence of N. tenuis. The synthetic insecticide lambda-cyhalothrin was used as a positive control. We also evaluated the sublethal effects of BCO on the behavior and predation rate of N. tenuis.

RESULTS

Our results demonstrated that BCO, alone and at its maximum recommended field rate for B. tabaci, was not effective in controlling the pest under laboratory conditions. Application of BCO simultaneous with N. tenuis release did not reduce the increase in the B. tabaci population. Effective control of B. tabaci was achieved using only N. tenuis. However, synthetic lambda-cyhalothrin pyrethroid, used here as a control, caused high pest mortality and led to on-site extinction of N. tenuis, which did not occur for insects exposed to BCO. Lambda-cyhalothrin and BCO significantly affected the foraging behavior of N. tenuis, reducing the predation rate, especially following exposure to lambda-cyhalothrin.

CONCLUSION

The insecticide lambda-cyhalothrin achieved satisfactory results in suppressing B. tabaci, but was harmful to N. tenuis. Additionally, lambda-cyhalothrin and BCO affected predator behavior. © 2020 Society of Chemical Industry.

How biological invasions affect animal behaviour: A global, cross-taxonomic analysis

In the Anthropocene, species are faced with drastic challenges due to rapid, human-induced changes, such as habitat destruction, pollution and biological invasions. In the case of invasions, native species may change their behaviour to minimize the impacts they sustain from invasive species, and invaders may also adapt to the conditions in their new environment in order to survive and establish self-sustaining populations. We aimed at giving an overview of which changes in behaviour are studied in invasions, and what is known about the types of behaviour that change, the underlying mechanisms and the speed of behavioural changes. Based on a review of the literature, we identified 191 studies and 360 records (some studies reported multiple records) documenting behavioural changes caused by biological invasions in native (236 records from 148 species) or invasive (124 records from 50 species) animal species. This global dataset, which we make openly available, is not restricted to particular taxonomic groups. We found a mild taxonomic bias in the literature towards mammals, birds and insects. In line with the enemy release hypothesis, native species changed their anti-predator behaviour more frequently than invasive species. Rates of behavioural change were evenly distributed across taxa, but not across the types of behaviour. Our findings may help to better understand the role of behaviour in biological invasions as well as temporal changes in both population densities and traits of invasive species, and of native species affected by them.

The omnivorous predator Macrolophus pygmaeus, a good candidate for the control of both greenhouse whitefly and poinsettia thrips on gerbera plants

The poinsettia thrips Echinothrips americanus Morgan is a relatively new pest that has spread rapidly worldwide and causes serious damage in both vegetable and ornamental plants. In this study, we investigated if and how effective this pest can be controlled in gerbera by the omnivorous predator Macrolophus pygmaeus (Rambur). Because herbivores on plants can interact through a shared predator, we also investigated how poinsettia thrips control is affected by the presence of the greenhouse whitefly Trialeurodes vaporariorum (Westwood), a pest that commonly coexists with E. americanus in gerbera. In laboratory studies, we found that the predator M. pygmaeus fed on both pests when offered together. Olfactometer tests showed a clear preference of the predators for plants infested by whiteflies but not by thrips. In a greenhouse experiment, densities of both pests on single gerbera plants were reduced to very low levels by the predator, either with both pests present together or alone. Hence, predator-mediated effects between whiteflies and thrips played only a minor role. The plant feeding of the shared predator probably reduced the dependence of predator survival and reproduction on the densities of the two pests, thereby weakening potential predator-mediated effects. Thus, M. pygmaeus is a good candidate for biological control of both pests in gerbera. However, further research is needed to investigate pest control at larger scales, when the pests can occur on different plants.

First Report Using a Native Lacewing Species to Control Tuta absoluta: From Laboratory Trials to Field Assessment

The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a destructive pest on tomato, has invaded most Afro-Eurasian countries. Recently invaded by the pest, most tomato crops in greenhouses and open fields in Tajikistan are currently suffering major damage. While failure in management using chemical insecticide has been frequently observed, alternative options such as biological control is urgently needed. In this study, we evaluated the effectiveness of the common green lacewing Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) against T. absoluta. In controlled laboratory conditions, C. carnea showed high predation rate on both T. absoluta eggs (i.e., 36 ± 2 eggs within 24 h and 72 ± 4 eggs within 48 h) and larvae, especially it can attack the larvae both inside and outside the leaf galleries (i.e., an average of 22% of the larvae was killed inside, and an average of 35% was killed outside). In a cage exclusion experiment, T. absoluta showed relatively low larval density in the cages with pre-fruiting release of C. carnea, whereas the larval density was four to six times higher in the “no release” cages. In the “post-fruiting release” cages, the pest population that had already built up during the pre-fruiting stage eventually crashed. In an open-field experiment, the tomato crops in control plots were fully destroyed, whereas low levels of larvae density and damage were observed in the biocontrol plots. Moreover, the field release of C. carnea resulted in significantly higher tomato yield than those without release, despite no differences between the “pre-fruiting release” and “post-fruiting release” treatments. We conclude that the local commercial biocontrol agent C. carnea could be promising for the management of T. absoluta in Tajikistan. It is also one of the first reports showing the management of T. absoluta using a lacewing species. The effectiveness should be validated by further field trials in larger area of commercial crops and various locations.

Prey preferences of notonectids towards larval mosquitoes across prey ontogeny and search area

BACKGROUND

Predatory biological control agents can be effective natural means of managing pests, vectors and invasive species. However, the strength of predator-prey interactions can be regulated through context-dependencies that often remain unquantified. In particular, refuge effects can influence the efficacy of biological agents towards target species, and such effects are often driven by prey size and search area differences. In this study, we quantify the prey preferences of two predaceous notonectids, Anisops breddini and Anisops sardeus, towards four different aquatic larval instar stages of the medically important mosquito Culex quinquefasciatus across variations in surface area and water depth.

RESULTS

Consumption rates differed significantly among the four larval sizes but not between the notonectids. Search area variations also elicited differences in consumption rates. Both predators tended to prefer second-instar mosquito prey among surface area and water depth variations, while generally avoiding the largest (fourth instar) and smallest (first instar) prey instar stages. For both predators, differential selectivity traits were emergent across surface area variations and water depth, with refuge effects for small prey generally greatest at intermediate-large depths with high surface areas. We thus demonstrate that predatory impacts of notonectids towards mosquito larvae differ significantly according to prey size, and likely peak at intermediate size classes.

CONCLUSION

Different mosquito size classes often coexist and compete, selectivity has important implications for adult mosquito proliferations. Further, in ephemeral aquatic habitats where surface areas and water depths are highly variable spatiotemporally, the efficacy of notonectids in controlling mosquito prey may differ substantially. © 2019 Society of Chemical Industry.

Spatio-temporal variations in wheat aphid populations and their natural enemies in four agro-ecological zones of Pakistan

Aphids are major pests of wheat crop in Pakistan inflicting considerable economic losses. A better knowledge of landscape scale spatial distribution of aphids and their natural enemies could be used to improve integrated pest management programs. Therefore, the present study aimed to document spatio-temporal variations in populations of wheat aphids and their natural enemies in Pakistan. The 2-year survey study was carried out at ten experimental farms located in five districts of four contrasted agro-ecological zones of eastern Pakistan (Punjab area) i.e. District Chakwal in arid zone, Gujranwala in rice-cropped zone, Faisalabad in central mixed-cropped zone, and Khanewal and Multan in cotton-cropped zone. The dominant aphid species i.e. Schizaphis graminum, Rhopalosiphum padi, R. maidis and Sitobion avenae varied significantly among the five districts surveyed. The population of S. graminum was observed more abundant in arid, R. padi in rice, S. avenae in aird and rice, and R. maidis in cotton-I zones. Aphids ended their population dynamics on 25^th March in central mixed-cropped zone and 12^th April in other three zones. Various species of natural enemies, mainly Coccinella septumpunctata, C. undecimpunctata, Menochilus sexmaculata, Chrysoperla carnea, Syrphidae and parasitoid mummies were inconsistently observed in four agro-ecological zones. The population of C. septumpunctata, was observed more abundant in rice zone, C. undecimpunctata and C. carnea in cotton-I and arid zones, M. sexmaculata in cotton-I and II zones, Syrphidae in cotton-I zone and parasitoid mummies in rice and arid zones. There were no clear relationships between aphid and the natural enemy populations. The present study may serve as a baseline regarding distribution of wheat aphids and their natural enemies and the results provided insights for further studies on the potential top-down (natural enemies) versus bottom-up (fertilization and irrigation regimes) forces in management of wheat aphids in eastern Pakistan.

Grassland harvesting alters ant community trophic structure: An isotopic study in tallgrass prairies

Disturbances have long been recognized as important forces for structuring natural communities but their effects on trophic structure are not well understood, particularly in terrestrial systems. This is in part because quantifying trophic linkages is a challenge, especially for small organisms with cryptic feeding behaviors such as insects, and often relies on conducting labor-intensive feeding trials or extensive observations in the field. In this study, we used stable isotopes of carbon and nitrogen to examine how disturbance (annual biomass harvesting) in tallgrass prairies affected the trophic position, trophic range, and niche space of ants, a widespread grassland consumer. We hypothesized that biomass harvest would remove important food and nesting resources of insects thus affecting ant feeding relationships and trophic structure. We found shifts in the feeding relationships inferred by isotopic signatures with harvest. In particular, these shifts suggest that ants within harvest sites utilized resources at lower trophic levels (possibly plant-based resources or herbivores), expanded trophic breadth, and occupied different niche spaces. Shifts in resource use following harvest could be due to harvest-mediated changes in both the plant and arthropod communities that might affect the strength of competition or alter plant nitrogen availability. Because shifts in resource use alter the flow of nutrients across the food web, disturbance effects on ants could have ecosystem-level consequences through nutrient cycling.

Potential for insecticide-mediated shift in ecological dominance between two competing aphid species

Competition is a key structuring component of biological communities, which is affected by both biotic and abiotic environmental stressors. Among the latter, anthropic stressors and particularly pesticides are noteworthy due to their intrinsic toxicity and large use in agroecosystems. However this issue has been scarcely documented so far. In this context, we carried out experiments under laboratory conditions to evaluate stress imposed by the neonicotinoid insecticide imidacloprid on intra and interspecific competition among two major wheat pest aphids. The bird cherry-oat aphid Rhopalosiphum padi L. and the English grain aphid Sitobion avenae F. were subjected to competition on wheat seedlings under varying density combinations of both species and subjected or not to imidacloprid exposure. Intraspecific competition does take place without insecticide exposure, but so does interspecific competition between both aphid species with R. padi prevailing over S. avenae. Imidacloprid interfered with both intra and interspecific competition suppressing the former and even the latter for up to 14 days, but not afterwards when a shift in dominance takes place favoring S. avenae over R. padi, in contrast with the interspecific competition without imidacloprid exposure. These findings hinted that insecticides are indeed able to mediate species interaction and competition influencing community structure and raising management concerns for favoring potential secondary pest outbreaks.

Prey-Stage Preference and Comparing Reproductive Performance of Aphidoletes aphidimyza (Diptera: Ceccidomyiidae) Feeding on Aphis gossypii (Hemiptera: Aphididae) and Myzus persicae

The predacious midge, Aphidoletes aphidimyza (Rondani), is an effective exclusive natural enemy of aphids in greenhouses and field crops. In this study, prey preference of A. aphidimyza was determined using seven treatments including different stages (third-instar nymphs and adults) of two prey species (Aphis gossypii Glover and Myzus persicae (Sulzer)) based on Manly's β preference index. Results of experiments consisting of two different preys showed that A. aphidimyza larvae consumed A. gossypii more than M. persicae, and the third nymphal stage of both species was preferred more, compared with adults. When all four types of prey were studied, Manly's index was 0.379, 0.235, 0.208, and 0.176 for nymphs of A. gossypii and M. persicae and adults of A. gossypii and M. persicae, respectively. Therefore, the nymphs of both species, as the most preferred prey, were used to study the reproductive performance of the predator in microcosm conditions. The significantly longer adult longevity (female: 7.62 ± 0.15, male: 7.42 ± 0.23 d), higher fecundity (93.75 ± 2.94 offspring per female), and higher intrinsic rate of increase (0.175 ± 0.009 d-1) of A. aphidimyza were obtained, while consuming third-instar nymphs of A. gossypii. Finally, this study indicated that third-instar nymphs of A. gossypii are the most suitable food for mass rearing of A. aphidimyza.

Effect of Age-Dependent Parasitism in Eggs of Tuta absoluta (Lepidoptera: Gelechiidae) on Intraguild Predation Between Nabis pseudoferus (Hemiptera: Nabidae) and Trichogramma brassicae (Hymenoptera: Trichogrammatidae)

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a destructive pest of tomato that can cause up to 100% yield loss. The predatory bug Nabis pseudoferus (Remane) (Hemiptera: Nabidae) and the parasitoid Trichogramma brassicae (Bezdenko) (Hymenoptera: Trichogrammatidae) are natural enemies of this pest. Since the interaction between predators and parasitoids in different trophic levels including intraguild predation (IGP) can decrease or increase the efficiency of natural enemies, the effects of age-dependent parasitism of host eggs on IGP between these two species were investigated under laboratory conditions. In no-choice and choice preference tests, the predatory bug was exposed to 40 parasitized and nonparasitized eggs of different ages (24, 48, and 72 h old). Investigation of switching behavior was conducted using various combinations of tomato leafminer eggs (30:90, 45:75, 60:60, 75:45, and 90:30 nonparasitized:parasitized eggs) using eggs of different ages (24, 48, and 72 h old). In no-choice tests, the highest feeding rate of the predatory bug was 39.21 ± 0.36 eggs on 24-h-old nonparasitized eggs and the lowest feeding rate was 1.4 ± 0.80 eggs on 72-h-old parasitized eggs. In choice tests, comparison of the Manly's β indices indicated that the predatory bug preferred to feed on nonparasitized eggs with 48- and 72-h-old eggs, but there was no significant preference for the 24-h-old eggs. Results of switching test showed that the linear regression between Manly's β index and different ratios of nonparasitized eggs to parasitized and nonparasitized eggs was not significant in 72-h-old eggs. However, this regression was significant with 24- and 48-h-old eggs and the predator's preference was dependent upon the ratio of nonparasitized and parasitized tomato leafminer eggs. Results of the current study showed that the increasing age of parasitized egg decreased intensity of IGP between N. pseudoferus and T. brassicae.

The function of supplemental foods for improved crop establishment of generalist predators Orius insidiosus and Dicyphus hesperus

As with many biological control agents, generalist predators rarely survive prolonged periods of prey scarcity. Towards improving crop establishment of two major predators used in North America, Orius insidiosus and Dicyphus hesperus, this study examined the role of supplemental foods in achieving greater predator survival and faster development. In controlled environment trials, developmental time and survival were compared for predators offered diets including Ephestia eggs, Artemia cysts, Typha pollen, or combinations of these. Nymphal developmental time was significantly shorter and survival greater for both predators reared on diets that included Ephestia eggs. Interestingly, D. hesperus could successfully complete nymphal development on Artemia cysts whereas O. insidiosus could not, alluding to fundamental physiological differences between these predators. In greenhouse assays, D. hesperus was more abundant after six weeks when offered diets that included Ephestia eggs either alone or in combination with pollen or Artemia cysts relative to other diets. In contrast, only diets of Ephestia eggs, Typha pollen or their combination could significantly increase O. insidiosus crop abundance relative to the unfed control. Together, this work highlights important differences in the relative values of supplemental foods for generalist predators used in crop protection. It is also meaningful in guiding biocontrol practitioners globally in the rapidly growing sector of greenhouse vegetable production.

Predator performance: inferring predator switching behaviors based on nutritional indices in a coccinellid-psylla-aphid system

BACKGROUND

Knowledge of the nutritional ecology of predatory coccinellids is important for the selection of efficient biocontrol agents. We examined five species common in pistachio orchards and determined their nutritional indices when fed on the key psylla pest of the system, Agonoscena pistaciae, in contrast to an alternative prey common on herbaceous plants in orchards, Aphis gossypii.

RESULTS

Feeding experiments revealed that Oenopia conglobata contaminata and Adalia bipunctata may be more efficient as biocontrol agents for A. pistaciae than for A. gossypii, as A. bipunctata had a high efficiency of conversion of ingested food and a high relative growth rate and O. conglobata contaminata had a high consumption index on psylla prey. In contrast, the nutritional indices of Coccinella undecimpunctata aegyptica, Hippodamia variegata and Exochomus nigripennis suggest that A. gossypii was a more suitable host food.

CONCLUSION

Where both the psyllids and the aphids occur in pistachio orchards, especially under conditions of unlimited access to A. gossypii, C. undecimpunctata aegyptica, H. variegata and E. nigripennis may prefer to move from psylla-infested leaves of pistachio trees and travel to and stay on weeds to feed on A. gossypii. The value of using nutritional ecology as a means of understanding and predicting biocontrol outcomes and selecting better candidates for mass rearing is discussed. © 2018 Society of Chemical Industry.

Foraging connections: Patterns of prey use linked to invasive predator diel movement

Invasive predators can profoundly impact native communities, especially in insular ecosystems where functionally equivalent predators were evolutionarily absent. Beyond direct consumption, predators can affect communities indirectly by creating or altering food web linkages among existing species. Where invasive predators consume prey from multiple distinct resource channels, novel links may couple the dynamics of disjunct modules and create indirect interactions between them. Our study focuses on invasive populations of Eleutherodactylus coqui (Anura: Leptodactylidae) on Hawaii Island. Coqui actively forage in the understory and lower canopy at night but return to the forest floor and belowground retreats by day. Recent dietary studies using gut contents and naturally occurring stable isotopes indicate higher than expected consumption of litter arthropods, which in these Hawaiian forests are primarily non-native species. We used laboratory studies to observe diurnal and nocturnal foraging behavior, and experimental field additions of C₄ vegetation as a litter tracer to distinguish epigaeic sources from food web pools in the C₃ canopy. Lab trials revealed that prey consumption during diurnal foraging was half that consumed during nocturnal foraging. Analysis of δ¹³C isotopes showed incorporation of C₄ carbon into litter arthropods within one month, and Bayesian mixing models estimated that 15–25% of the carbon in coqui tissue was derived from litter sources. These results support recent findings that E. coqui are not quiescent diurnally but instead actively forage. Such activity by a mobile invasive predator may introduce a novel linkage that integrates detrital and foliar resource pools, potentially distributing influences of invasive litter arthropods through the broader system to amplify impacts on native species.

Dynamics of Predation on Lygus hesperus (Hemiptera: Miridae) in Alfalfa Trap-Cropped Organic Strawberry

Alfalfa (Medicago sativa L.) (Fabales: Fabaceae) can be strategically planted as a trap crop for Lygus spp. in California's organic strawberry fields. Alfalfa has been shown to attract both Lygus spp. and, in turn, a Lygus-specific parasitoid, Peristenus relictus (Ruthe) (Hymenoptera: Braconidae). However, the impact of alfalfa trap-cropped strawberries on the Lygus spp. predator complex is unknown. Here we identify key predators of Lygus spp. found in organic strawberry. First, a general survey was conducted at an organic, non-trap cropped strawberry farm, to quantify predator abundance and to qualitatively assess their feeding activity on Lygus spp. We identified the 11 most abundant predator taxa present and, by using a Lygus-specific PCR assay, determined that about 18% of the insects and spiders contained Lygus spp. remains in their guts. We then conducted a study to examine alfalfa's role in conserving the most relevant predators in trap-cropped organic strawberries. Specifically, we quantified predator abundance and qualitatively measured predator feeding activity (by gut analysis) on Lygus spp. collected in strawberry plots either lacking or containing an alfalfa trap crop. Data revealed that some predator taxa, including the numerically dominant predator, Orius tristicolor (White) (Hemiptera: Anthocoridae), aggregated in alfalfa trap crops. The gut content analyses revealed that insect and spider predators collected from the alfalfa trap crop had a significantly higher proportion of their population containing Lygus spp. remains than those collected from nearby rows of strawberries. These results suggest that alfalfa trap cropping might be a useful tactic for conserving the biological control services of generalist predators in organically grown strawberries in California.

Opportunistic random searcher versus intentional search image user

We consider two types of optimal foragers: a random searcher and a search image user. A search image user can find its desired prey with higher and undesired prey with lower probability than a random searcher. Our model considers the density-dependent travelling time and the time duration of reproduction (oviposition). In the framework of optimal foraging theory for one predator-two prey systems, we find that there are ranges of prey densities in which the search image user has a higher net energy intake, and there are other ranges of prey densities in which the random searcher has higher net energy intake. The damsel bug Nabis pseudoferus Remane (Hemiptera: Nabidae) is a generalist predator rather than an omnivore. This species has a wide range of arthropod prey (predominantly insects and mites). Several aspects of the biology of this species have been studied, especially its cannibalistic behaviour, which is a quite important feature because N. pseudoferus is often used as a biological control agent against lepidopteran pests in greenhouse crops. Experimentally, we found that Nabis is a search image user in the above sense.

Ecology, Worldwide Spread, and Management of the Invasive South American Tomato Pinworm, Tuta absoluta: Past, Present, and Future

The South American tomato pinworm, Tuta absoluta (Meyrick), is native to the western Neotropics. After invading Spain in 2006, it spread rapidly throughout Afro-Eurasia and has become a major threat to world tomato production. Integrated pest management (IPM) strategies have been developed, but widespread insecticide use has caused selection for insecticide resistance as well as undesirable effects on key beneficial arthropods. Augmentation and conservation biological control relying on omnivorous mirid predators has proved successful for management of T. absoluta, where implementation is dependent on abiotic, biotic (e.g., alternative prey), and anthropogenic factors (e.g., pesticides). Research has been carried out on larval parasitoids, showing potential for further development of sustainable control. The development of resistant tomato varieties is ongoing, but they are not commercially available yet. Knowledge gaps remain to be filled to optimize IPM packages on tomato crops and to help prevent further spread worldwide.

A landscape genetic analysis of important agricultural pest species in Tunisia: The whitefly Bemisia tabaci

Combining landscape ecology and genetics provides an excellent framework to appreciate pest population dynamics and dispersal. The genetic architectures of many species are always shaped by environmental constraints. Because little is known about the ecological and genetic traits of Tunisian whitefly populations, the main objective of this work is to highlight patterns of biodiversity, genetic structure and migration routes of this pest. We used nuclear microsatellite loci to analyze B. tabaci populations collected from various agricultural areas across the country and we determine their biotype status. Molecular data were subsequently interpreted in an ecological context supplied from a species distribution model to infer habitat suitability and hereafter the potential connection paths between sampling localities. An analysis of landscape resistance to B. tabaci genetic flow was thus applied to take into account habitat suitability, genetic relatedness and functional connectivity of habitats within a varied landscape matrix. We shed light on the occurrence of three geographically delineated genetic groups with high levels of genetic differentiation within each of them. Potential migration corridors of this pest were then established providing significant advances toward the understanding of genetic features and the dynamic dispersal of this pest. This study supports the hypothesis of a long-distance dispersal of B. tabaci followed by infrequent long-term isolations. The Inference of population sources and colonization routes is critical for the design and implementation of accurate management strategies against this pest.

Population genetic structure of the biological control agent Macrolophus pygmaeus in Mediterranean agroecosystems

Biological control of agricultural pests relies on knowledge of agroecosystem functionality, particularly when affected by the use of mass-produced biological agents. Incorporating pre- and/or post-release information such as genetic diversity and structure on these agents using molecular-based approaches could advance our knowledge of how they perform in agroecosystems. We evaluated the population genetics of Macrolophus pygmaeus, the most widely used predatory mirid against many arthropod pests of greenhouse crops in the Mediterranean region, using the mitochondrial Cytb sequence and microsatellite data, and population genetics and phylogeny approaches. We investigated commercially mass-produced insects (i.e., commercial insects either mass-reared in the laboratory for many generations, or purchased by farmers and released in the greenhouses) and "wild" insects (i.e., that occur naturally outside or are collected in nature for release in the greenhouses). The mirids were mainly collected in agroecosystems in which solanaceous plants are grown in northern Spain, southern France and Greece. Both molecular markers and approaches distinguished 2 genetically differentiated populations. The less genetically diverse population, hereafter named the "commercial" strain included all individuals from laboratory mass-rearings and most releases of commercially bred individuals. The most genetically diverse population mainly comprised individuals originating from noncultivated environments, or from releases of "wild" individuals. Rare examples of hybridization between M. pygmaeus from the 2 populations were observed and asymmetric gene flow was revealed. These findings provide new insights into what happens to M. pygmaeus released in the agroecosystems we studied, and show that it is possible to monitor some commercial strains.

Survival of a specialist natural enemy experiencing resource competition with an omnivorous predator when sharing the invasive prey Tuta absoluta

Can specialist natural enemies persist in ecosystems when competing with omnivorous natural enemies for their shared prey? The consequences of omnivory have been studied theoretically, but empirical studies are still lacking. Omnivory is nevertheless common in nature and omnivorous predators coexist with specialists in many ecosystems, even when they are intraguild predators. This type of association is also common in agroecosystems in which biological control strategies are used. Our study provides an example of the outcome of such an association in the context of biological control of the invasive pest Tuta absoluta (Lepidoptera) in a tomato agroecosystem. The two natural enemies involved, that is, a specialist (Stenomesius japonicus (Hymenoptera) parasitoid) and an omnivore (Macrolophus pygmaeus (Hemiptera) predator), were able to coexist for 3 months in our experimental cages in the absence of metacommunity mechanisms (i.e., emigration and recolonization), contrary to theoretical expectations. However, they negatively affected each other's population dynamics. We found that spatial resource segregation was not a mechanism that promoted their coexistence. Regarding pest control, the specialist and omnivorous natural enemies were found to exhibit complementary functional traits, leading to the best control when together. Mechanisms that may have promoted the coexistence of the two species as well as consequences with regard to the inoculative biological control program are discussed.

Does Long-Term Feeding on Alternative Prey Affect the Biological Performance of Neoseiulus barkeri (Acari: Phytoseiidae) on the Target Spider Mites?

The predatory mite Neoseiulus barkeri (Hughes) is a good biological control agent for many small sucking pests. We aimed to determine whether rearing long term on alternative prey versus target prey species affected the performance of N. barkeri. Therefore, we investigated the prey preference, life tables, and population parameters of N. barkeri between alternative prey Tyrophagus putrescentiae (Schrank) and three species of spider mites, Tetranychus urticae Koch, Panonychus citri (McGregor), and Eotetranychus kankitus Ehara. We found that N. barkeri preferred the tetranychid mites to the alternative prey. Between the tetranychid mites, the predator consumed more P. citri and E. kankitus than T. urticae. When reared on T. urticae, the total developmental time and longevity of N. barkeri were the longest, whereas the intrinsic rate of increase was the lowest, indicating that the biotic fitness of predatory mite preyed on target of T. urticae was higher than on alternative prey of T. putrescentiae. However, total developmental time, longevity, and fecundity did not differ between N. barkeri reared on T. putrescentiae and P. citri, although these parameters were higher than those for mites reared on E. kankitus, indicating that the predatory mite reared on T. putrescentiae may not be affected to control P. citri, and that coexistence of P. citri and E. kankitus may enhance the control efficiency of N. barkeri. Altogether, our results demonstrated that long-term feeding on the alternative prey T. putrescentiae did not affect the performance of the predatory mite N. barkeri on various target spider mites.

Nutritional physiology and ecology of wildlife in a changing world

Over the last century, humans have modified landscapes, generated pollution and provided opportunities for exotic species to invade areas where they did not evolve. In addition, humans now interact with animals in a growing number of ways (e.g. ecotourism). As a result, the quality (i.e. nutrient composition) and quantity (i.e. food abundance) of dietary items consumed by wildlife have, in many cases, changed. We present representative examples of the extent to which vertebrate foraging behaviour, food availability (quantity and quality) and digestive physiology have been modified due to human-induced environmental changes and human activities. We find that these effects can be quite extensive, especially as a result of pollution and human-provisioned food sources (despite good intentions). We also discuss the role of nutrition in conservation practices, from the perspective of both in situ and ex situ conservation. Though we find that the changes in the nutritional ecology and physiology of wildlife due to human alterations are typically negative and largely involve impacts on foraging behaviour and food availability, the extent to which these will affect the fitness of organisms and result in evolutionary changes is not clearly understood, and requires further investigation.

Life-History Traits of Macrolophus pygmaeus with Different Prey Foods

Macrolophus pygmaeus Rambur (Hemiptera: Miridae) is a generalist predatory mirid widely used in augmentative biological control of various insect pests in greenhouse tomato production in Europe, including the invasive tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera, Gelechiidae). However, its biocontrol efficacy often relies on the presence of alternative prey. The present study aimed at evaluating the effect of various prey foods (Ephestia kuehniella eggs, Bemisia tabaci nymphs, Tuta absoluta eggs and Macrosiphum euphorbiae nymphs) on some life history traits of M. pygmaeus. Both nymphal development and adult fertility of M. pygmaeus were significantly affected by prey food type, but not survival. Duration of nymphal stage was higher when M. pygmaeus fed on T. absoluta eggs compared to the other prey. Mean fertility of M. pygmaeus females was greatest when fed with B. tabaci nymphs, and was greater when offered M. euphorbiae aphids and E. kuehniella eggs than when offered T. absoluta eggs. Given the low quality of T. absoluta eggs, the efficacy of M. pygmaeus to control T. absoluta may be limited in the absence of other food sources. Experiments for assessing effectiveness of generalist predators should involve the possible impact of prey preference as well as a possible prey switching.

Experimental Test of Preferences for an Invasive Prey by an Endangered Predator: Implications for Conservation

Identifying impacts of exotic species on native populations is central to ecology and conservation. Although the effects of exotic predators on native prey have received much attention, the role of exotic prey on native predators is poorly understood. Determining if native predators actively prefer invasive prey over native prey has implications for interpreting invasion impacts, identifying the presence of evolutionary traps, and predator persistence. One of the world’s most invasive species, Pomacea maculata, has recently established in portions of the endangered Everglade snail kite’s (Rostrhamus sociabilis plumbeus) geographic range. Although these exotic snails could provide additional prey resources, they are typically much larger than the native snail, which can lead to lower foraging success and the potential for diminished energetic benefits in comparison to native snails. Nonetheless, snail kites frequently forage on exotic snails. We used choice experiments to evaluate snail kite foraging preference in relation to exotic species and snail size. We found that snail kites do not show a preference for native or exotic snails. Rather, snail kites generally showed a preference for medium-sized snails, the sizes reflective of large native snails. These results suggest that while snail kites frequently forage on exotic snails in the wild, this behavior is likely driven simply by the abundance of exotic snails rather than snail kites preferring exotics. This lack of preference offers insights to hypotheses regarding effects of exotic species, guidance regarding habitat and invasive species management, and illustrates how native-exotic relationships can be misleading in the absence of experimental tests of such interactions.

Presence of Native Prey Does Not Divert Predation on Exotic Pests by Harmonia axyridis in Its Indigenous Range

In China, two invasive pests, Bemisia tabaci MEAM1 (Gennadius) and Frankliniella occidentalis (Pergande), often co-occur with the native pest, Aphis gossypii (Glover), on plants of Malvaceae and Cucurbitaceae. All three are preyed on by the native ladybird, Harmonia axyridis (Pallas); however, the native predator might be expected to prefer native prey to the exotic ones due to a shared evolutionary past. In order to clarify whether the presence of native prey affected the consumption of these two invasive species by the native predator, field-cage experiments were conducted. A duplex qPCR was used to simultaneously detect both non-native pests within the gut of the predator. H. axyridis readily accepted both invasive prey species, but preferred B. tabaci. With all three prey species available, H. axyridis consumption of B. tabaci was 39.3±2.2% greater than consumption of F. occidentalis. The presence of A. gossypii reduced (by 59.9% on B. tabaci, and by 60.6% on F. occidentalis), but did not stop predation on the two exotic prey when all three were present. The consumption of B. tabaci was similar whether it was alone or together with A. gossypii. However, the presence of aphids reduced predation on the invasive thrips. Thus, some invasive prey may be incorporated into the prey range of a native generalist predator even in the presence of preferred native prey.

Control of the Tomato Leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), in Open-Field Tomatoes by Indigenous Natural Enemies Occurring in Israel

The tomato leafminer, Tuta absoluta (Meyrick), had established in Israel by 2010, attacking both open-field tomatoes and greenhouse crops.We searched for its natural enemies in open-field tomatoes, and tried to determine their potential for controlling this pest. We surveyed the local natural enemies in open tomato fields and measured their impact on pest populations in an unsprayed field. We assessed the suppressive ability of the dominant hemipteran predator, Nesidiocoris tenuis Reuter, against T. absoluta under controlled laboratory conditions and evaluated the impact of its augmentation on T. absoluta control in open-field tomatoes. We found five natural enemy species:the predator, N. tenuis, two braconids, and two eulophids. Predation accounted for 64.5±9.2% (mean ± SE) of T. absoluta larval mortality, whereas parasitism accounted for 20.96±7.5%. Together, they eliminated the pest population at tomato harvest time. Under controlled conditions, predation by N. tenuis rose from 58 to 72% with increased density of T. absoluta, suggesting positive density dependence. The reduction of T. absoluta (83%) by N. tenuis was higher than that of Bemisia tabaci (32%), suggesting a preference of N. tenuis for T. absoluta. Augmentation of N.tenuis was as effective as conventional treatment insecticide treatment, and plant damage was low and did not seem to affect yield. Results indicate that reduced pesticide use enables indigenous natural enemies, particularly N.tenuis, to successfully control T. absoluta and prevent crop damage in open-field tomatoes.

Predation on the Invasive Copepod, Pseudodiaptomus forbesi, and Native Zooplankton in the Lower Columbia River: An Experimental Approach to Quantify Differences in Prey-Specific Feeding Rates

Invasive planktonic crustaceans have become a prominent feature of aquatic communities worldwide, yet their effects on food webs are not well known. The Asian calanoid copepod, Pseudodiaptomus forbesi, introduced to the Columbia River Estuary approximately 15 years ago, now dominates the late-summer zooplankton community, but its use by native aquatic predators is unknown. We investigated whether three species of planktivorous fishes (chinook salmon, three-spined stickleback, and northern pikeminnow) and one species of mysid exhibited higher feeding rates on native copepods and cladocerans relative to P. forbesi by conducting `single-prey' feeding experiments and, additionally, examined selectivity for prey types with `two-prey' feeding experiments. In single-prey experiments individual predator species showed no difference in feeding rates on native cyclopoid copepods (Cyclopidae spp.) relative to invasive P. forbesi, though wild-collected predators exhibited higher feeding rates on cyclopoids when considered in aggregate. In two-prey experiments, chinook salmon and northern pikeminnow both strongly selected native cladocerans (Daphnia retrocurva) over P. forbesi, and moreover, northern pikeminnow selected native Cyclopidae spp. over P. forbesi. On the other hand, in two-prey experiments, chinook salmon, three-spined stickleback and mysids were non- selective with respect to feeding on native cyclopoid copepods versus P. forbesi. Our results indicate that all four native predators in the Columbia River Estuary can consume the invasive copepod, P. forbesi, but that some predators select for native zooplankton over P. forbesi, most likely due to one (or both) of two possible underlying casual mechanisms: 1) differential taxon-specific prey motility and escape responses (calanoids > cyclopoids > daphnids) or 2) the invasive status of the zooplankton prey resulting in naivety, and thus lower feeding rates, of native predators feeding on invasive prey.

Effect of plant nitrogen and water status on the foraging behavior and fitness of an omnivorous arthropod

Omnivorous arthropods make dietary choices according to the environment in which they forage, mainly availability/quality of plant and/or prey resources. Such decisions and their subsequent impacts on life‐history traits may be affected by the availability of nutrients and water to plants, that is, through bottom‐up forces. By setting up arenas for feeding behavior observation as well as glasshouse cages for plant preference assessment, we studied effects of the presence of prey (Lepidoptera eggs) and nitrogen/water availability to host tomato plants on the foraging behavior and life‐history traits in the omnivorous predator Macrolophus pygmaeus (Heteroptera: Miridae). In the absence of prey, the predator fed equally on the plants treated with various levels of nitrogen and water. In the presence of prey, however, the feeding rate on plants decreased when the plant received low water input. The feeding rate on prey was positively correlated with feeding rate on plants; that is, prey feeding increased with plant feeding when the plants received high water input. Moreover, plants receiving high water input attracted more M. pygmaeus adults compared with those receiving low water input. For M. pygmaeus fitness, the presence of prey enhanced its fertility and longevity, but the longevity decreased when plants received low compared with high water input. In conclusion, the omnivorous predator may be obliged to feed on plants to obtain water, and plant water status may be a limiting factor for the foraging behavior and fitness of the omnivorous predator.

Prey Preference and Life Table of Amblyseius orientalis on Bemisia tabaci and Tetranychus cinnabarinus

Amblyseius orientalis (Ehara) (Acari: Phytoseiidae) is a native predatory mite species in China. It used to be considered as a specialist predator of spider mites. However, recent studies show it also preys on other small arthropod pests, such as Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Experiments were conducted to investigate (1) prey preference of A. orientalis between Tetranychus cinnabarinus (Boisd.) (Acari: Tetranychidae) and B. tabaci, and (2) development, consumption and life table parameters of A. orientalis when reared on T. cinnabarinus, B. tabaci or a mix of both prey species. When preying on different stages of T. cinnabarinus, A. orientalis preferred protonymphs, whereas when preying on different stages of B. tabaci, A. orientalis preferred eggs. When these two most preferred stages were provided together (T. cinnabarinus protonymphs and B. tabaci eggs), A. orientalis randomly selected its prey. Amblyseius orientalis was able to complete its life cycle on B. tabaci eggs, T. cinnabarinus protonymphs, or a mix of both prey. However, its developmental duration was 53.9% and 30.0% longer when reared on B. tabaci eggs than on T. cinnabarinus and a mix of both prey, respectively. In addition, it produced only a few eggs and its intrinsic rate of increase was negative when reared on B. tabaci eggs, which indicates that B. tabaci is not sufficient to maintain A. orientalis population. The intrinsic rates of increase were 0.16 and 0.23 when A. orientalis was fed on the prey mix and T. cinnabarinus, respectively. These results suggest that although B. tabaci is a poor food resource for A. orientalis in comparison to T. cinnabarinus, A. orientalis is able to sustain its population on a mix of both prey. This predatory mite may thus be a potential biological control agent of B. tabaci when this pest co-occurs with the alternative minor pest T. cinnabarinus.

Foraging behaviour of the parasitoid Eretmocerus eremicus under intraguild predation risk by Macrolophus pygmaeus

BACKGROUND

Intraguild predation (IGP), predation between species that use a common resource, can affect the populations of a pest, of the pest's natural enemy (IG prey) and of the predator of the pest's natural enemy (IG predator). In this study, we determined whether the parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) (IG prey), modifies its foraging behaviour under the risk of IGP by Macrolophus pygmaeus (Hemiptera: Miridae) (IG predator). Parasitoid behaviour was analysed using two bioassays (choice and no-choice) with the following treatments: (i) control, tomato leaf infested with whitefly nymphs; and (ii) PEP, tomato leaf infested with whitefly nymphs and previously exposed to the IG predator; and (iii) PP, tomato leaf infested with whitefly nymphs, with both, the IG predator and the IG prey present.

RESULTS

In both bioassays, we found that E. eremicus did not significantly modify the number of ovipositions, time of residence, duration of oviposition or behavioural sequence. However, in the no-choice bioassay, the number of attacks was higher and their duration shorter in the PEP treatment than in the control.

CONCLUSION

Our results indicate that the parasitoid may detect IGP risk to a certain extent, but it did not significantly modify its foraging behaviour, suggesting that simultaneous release of the two natural enemies can be successfully employed.