Dispersal of aphids, whiteflies and their natural enemies under photoselective nets

Integrated Pest Management of insects includes several control tactics, such as the use of photoselective nets, which may reduce the flight activity of insects. Limiting the dispersal of pests such as aphids and whiteflies is important because of their major role as vectors of plant viruses, while a minor impact on natural enemies is desired. In this study, we examined for the first time the dispersal ability of three vector species, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae) and Myzus persicae (Sulzer) (Hemiptera: Aphididae), in cages covered with photoselective nets. Contrary to the results obtained with aphids, the ability of the whitefly B. tabaci, to reach the target plant was reduced by photoselective nets. In a second set of experiments, the impact of UV-absorbing nets on the visual cues of two important predator species, Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae), was evaluated. The anthocorid was caught in higher numbers in traps placed under regular nets, whereas the mites preferably chose environments in which the UV radiation was attenuated. We have observed a wide range of effects that impedes generalization, although photoselective nets have a positive effect on pest management of whiteflies and aphids under protected environments.     

Aphid orientation and performance in glasshouses under different UV‐A/UV‐B radiation regimes

Visual cues leading to host selection and landing are of major importance for aphids and evidence suggests that flight activity is very dependent on ultraviolet (UV)‐A radiation in the environment. At the same time research on insect plant hosts suggest that the UV‐B component can deter some pests via changes in secondary metabolite chemistry. Here, we examine the potential of UV (UV‐A/UV‐B) radiation to control insect pests in the glasshouse environment. We first examined artificial exposure to UV‐B and the potential to trigger morphological and biochemical modifications in pepper (Capsicum annuum L., Solanaceae) with implications for the fitness of green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). UV‐B caused accumulation of leaf secondary metabolites and soluble carbohydrates, and stimulated photosynthetic pigments. However, UV‐B did not impact on foliar protein content and aphid performance was unaffected. Next, we studied how altering the UV‐A/UV‐B ratio environment affected aphid orientation and spatial distribution over time, either directly or by exposing plants to supplemental UV before insect introduction. Aphids directly settled and dispersed on their host pepper plants more readily in the presence of supplemental UV‐A and UV‐B. In the control treatment with ambient glasshouse UV‐A and UV‐B, insects remained more aggregated. Furthermore, insects were less attracted to peppers pre‐exposed to supplemental UV‐A and UV‐B radiation. Our results suggest that suppression of UV‐A and UV‐B inside the protected environment reduces aphid colonization and dispersal. Furthermore, application of moderate exposure of young pepper plants to supplemental UV‐B radiation could aid in protection from the colonization by phytophagous insects.     

Parasitoids aid dispersal of a nonpersistently transmitted plant virus by disturbing the aphid vector

• 1 Aphids are the major group of insects that vector plant viruses, and they often display a preference for foliage showing disease symptoms. Although this behaviour will increase the numbers of vectors acquiring the pathogen, it will not in itself result in a greater spread of the disease.
• 2 The present study examined how infection of Vicia faba by the nonpersistently transmitted virus bean yellow mosaic virus (BYMV) affected colonization by pea aphids Acyrthosiphon pisum. We then examined how foraging by the hymenopterous parasitoid Aphidius ervi affected aphid settling/movement behaviour and the consequences for dissemination of the virus.
• 3 In Petri dish arenas, aphids colonized discs from BYMV‐infected leaves more rapidly than discs from uninfected plants. Reflectance from infected foliage was approximately 20% higher than from uninfected leaves in the green–yellow wavelengths, indicating that aphids might be responding to visual cues from the brighter foliage. Settling was reduced by A. ervi, with the foraging wasps preventing the aphids reaching and/or remaining on the leaf tissue.
• 4 In multiple plant arenas, A. ervi caused a reduction in aphid numbers but also a nine‐fold increase in BYMV infection. It is hypothesized that disturbance by the parasitoids resulted in more aphid movement as well as more cases of aphids probing on a BYMV‐infected plant and then a new host within the critical time period for successful inoculation to occur. This effect of parasitoids on virus dispersal should be considered in epidemiological models of insect‐vectored plant diseases, and also when evaluating the use of natural enemies in biocontrol strategies of insect herbivore/vector pests.

     

The use of ultraviolet-blocking films in insect pest management in the UK; effects on naturally occurring arthropod pest and natural enemy populations in a protected cucumber crop

Studies in polytunnels were conducted to investigate the effects of ultraviolet (UV)‐blocking films on naturally occurring insect pests and their arthropod natural enemies on a cucumber crop. Within tunnels clad with Antibotrytis (blocks light < 400 nm) and UVI/EVA (UV transmitting), 5.8 and 23.4 times more aphids, respectively, were recorded on traps compared with those on traps within tunnels clad with XL 385 (blocks light < 385 nm). When all plants within the UVI/EVA tunnels had become heavily infested with aphids, half of the plants in XL 385 tunnels were uninfested. More Coleoptera and thrips (approximately two times) were recorded under the UVI/EVA film than under the UV‐blocking films, but for other arthropod pests (e.g. whitefly, leafhoppers), clear conclusions could not be drawn as low numbers were recorded. Substantial numbers of chalcid parasitoids and syrphids were found under the UV‐blocking films, but further research is needed to evaluate fully the effect of such films on biological control of aphids. Higher syrphid numbers and more aphid mummies were recorded under the UVI/EVA film, probably because of the higher numbers of aphids present in tunnels clad with this film. The potential that UV‐blocking films have as an effective component of commercial Integrated Pest Management (IPM) systems, for protected horticultural crops, is discussed.     

How does atmospheric elevated CO2 affect crop pests and their natural enemies? Case histories from China

Abstract Global atmospheric CO₂ concentrations have risen rapidly since the Industrial Revolution and are considered as a primary factor in climate change. The effects of elevated CO₂ on herbivore insects were found to be primarily through the CO₂‐induced changes occurring in their host plants, which then possibly affect the intensity and frequency of pest outbreaks on crops. This paper reviews several ongoing research models using primary pests of crops (cotton bollworm, whitefly, aphids) and their natural enemies (ladybeetles, parasitoids) in China to examine insect responses to elevated CO₂. It is generally indicated that elevated CO₂ prolonged the development of cotton bollworm, Helicoverpa armigera, a chewing insect, by decreasing the foliar nitrogen of host plants. In contrast, the phloem‐sucking aphid and whitefly insects had species‐specific responses to elevated CO₂ because of complex interactions that occur in the phloem sieve elements of plants. Some aphid species, such as cotton aphid, Aphis gossypii and wheat aphid, Sitobion avenae, were considered to represent the only feeding guild to respond positively to elevated CO₂ conditions. Although whitefly, Bemisia tabaci, a major vector of Tomato yellow leaf curl virus, had neutral response to elevated CO₂, the plants became less vulnerable to the virus infection under elevated CO₂. The predator and parasitoid response to elevated CO₂ were frequently idiosyncratic. These documents from Chinese scientists suggested that elevated CO₂ initially affects the crop plant and then cascades to a higher trophic level through the food chain to encompass herbivores (pests), their natural enemies, pathogens and underground nematodes, which disrupt the natural balance observed previously in agricultural ecosystems.     

Host plants and natural enemies of Bemisia tabaci (Hemiptera: Aleyrodidae) in China

Abstract The sweetpotato whitefly, Bemisia tabaci, has been a destructive pest in China for over the past two decades. It is an extremely polyphagous insect, being recorded feeding on hundreds of host plants around the world. Potential host plants and natural enemies of B. tabaci in the south, southeast, middle, north and northwest of China were investigated during the last decade. In total 361 plant species from 89 families were recorded in our surveys. Plants in the families Compositae, Cruciferae, Cucurbitaceae, Solanaceae and Leguminosae were the preferred host species for B. tabaci, which therefore suffered much damage from this devastating pest due to their high populations. In total, 56 species of parasitoids, 54 species of arthropod predators and seven species of entomopathogenic fungi were recorded in our surveys. Aphelinid parasitoids from Encarsia and Eretmocerus genera, lady beetles and lacewings in Coleoptera and Neuroptera were found to be the dominant arthropod predators of B. tabaci in China. The varieties of host plant, their distribution and the dominant species of natural enemies of B. tabaci in different regions of China are discussed.     

Entomopathogenic fungi stimulate transgenerational wing induction in pea aphids,Acyrthosiphon pisum (Hemiptera: Aphididae)

1. Aphid natural enemies include not only predators and parasitoids but also pathogens, of which fungi are the most studied for biological control. While wing formation in aphids is induced by abiotic conditions, it is also affected by biotic interactions with their arthropod natural enemies. Wing induction via interactions with arthropod natural enemies is mediated by the increase in their physical contact when alarmed (pseudo‐crowding). Pathogenic fungi do not trigger this alarm behaviour in aphids and, therefore, no pseudo‐crowding occurs. 2. We hypothesise that, while pathogenic fungi will stimulate maternally induced wing formation, the mechanism is different and is influenced by pathogen specificity. We tested this hypothesis using two entomopathogenic fungi, Pandora neoaphidis and Beauveria bassiana, an aphid specialist and a generalist respectively, on the pea aphid, Acyrthosiphon pisum Harris. 3. We first demonstrate that pea aphids infected with either pathogen and maintained in groups on broad bean plants produced a higher proportion of winged morphs than uninfected control aphids. We then show that, when maintained in isolation, aphids infected with either pathogen also produced higher proportions of winged offspring than control aphids. There was no difference between P. neoaphidis and B. bassiana in their effects on wing induction in either experiment. 4. Unlike the effect of predators and parasitoids on pea aphid wing induction, the effect of pathogens is independent of physical contact with other aphids, suggesting that physiological cues induce wing formation in infected aphids. It is possible that aphids benefit from wing induction by escaping infected patches whilst pathogens may benefit through dispersion. Possible mechanisms of wing induction are discussed.     

Colored shading nets impede insect invasion and decrease the incidences of insect‐transmitted viral diseases in vegetable crops

Black shading nets are commonly used to protect agricultural crops from excessive solar radiation and wind, and for water saving. Recent studies have demonstrated that when black nets were replaced by either red, yellow, or pearl nets (ChromatiNets^?) of equivalent shading capacity, it increased the fruit yield and improved the quality of bell peppers (Capsicum annuum L.) and tomatoes (Solanum lycopersicum L.) (both Solanaceae). We studied the effects of these colored shading nets on the infestation by aphids [Myzus persicae (Sulzer) and Aphis gossypii Glover (both Hemiptera: Aphididae)] and whiteflies [Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)], and the incidence of the viral diseases transmitted by these insects, for five consecutive years (2006–2010). These studies were conducted in the semi‐arid Besor region in southern Israel. The plants were grown in ‘walk‐in’ tunnels that were covered by several nets of 35% shading capacity in the range of photosynthetically active radiation. Although the shading nets permit free passage of these pests, the infestation levels of aphids and whiteflies in tunnels covered by either the yellow or pearl nets were consistently 2–3× lower than in tunnels covered by the black or red nets. In accordance with the pest results, when the incidences of Cucumber mosaic virus in pepper grown under the black or red nets ranged between 35 and 89%, they were 2–10× lower under the yellow or pearl nets. Similarly, when the incidences of necrotic Potato virus Y in tomato grown under black or red nets ranged between 42 and 50%, they were 2–3× lower under the yellow or pearl nets. Also, when the incidences of Tomato yellow leaf curl virus in tomato grown under the black or red nets ranged between 15 and 50%, but they were 2–4× lower under the yellow or pearl nets. Putative mechanisms of crop protection achieved by the yellow and pearl nets are discussed.     

Females of Cotesia vestalis,a parasitoid of diamondback moth larvae,learn to recognise cues from aphid‐infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non‐host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naïve parasitoids exhibited no preference between aphid‐infested and uninfested plants in a dual‐choice test, but those that had been previously fed aphid honeydew significantly preferred aphid‐infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid‐infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.     

Odour masking of tomato volatiles by coriander volatiles in host plant selection of Bemisia tabaci biotype B

The silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important pest insects in tomato crop systems worldwide. It has been previously demonstrated that intercropping tomato [Solanum lycopersicum L. Mill. (Solanaceae)] with coriander [Coriandrum sativum L. (Apiaceae)] reduces the incidence and severity of damage caused by B. tabaci. However, it is not yet known how coriander affects the insect′s behaviour. We evaluated the attractiveness of tomato constitutive volatiles to B. tabaci and what effect coriander constitutive volatiles have on the insect′s behaviour. To this end, we conducted three bioassays in a multiple‐choice four‐arm olfactometer (‘×’ type), measuring B. tabaci behaviour when offered tomato and coriander constitutive volatiles presented alone as well as together. We also evaluated the colonisation and establishment of B. tabaci in experimental plots with only single tomato plants and tomatoes intercropped with coriander in a greenhouse. Bemisia tabaci males and females recognised tomato constitutive volatiles as a positive stimulus (kairomonal effect), indicating that semiochemicals from this plant can play an important role in the insect’s host plant selection. Coriander constitutive volatiles reduced the attractiveness of tomato volatiles but no repellency to these volatiles was observed. Greater numbers of adults and nymphs of B. tabaci per plant were observed in tomato monoculture plots than in tomato intercropped with coriander. We suggest that coriander constitutive volatiles have an odour masking effect on tomato volatiles, thus interfering in the host plant selection of B. tabaci.     

Seasonal variation in natural mortality factors of Tuta absoluta (Lepidoptera: Gelechiidae) in open‐field tomato cultivation

The seasonal variation in natural mortality of phytophagous insects is determined by the relative importance of biotic and abiotic factors in agroecosystems. Knowledge regarding these factors throughout the year represents a key concern for IPM programmes. Seasonal population fluctuations of tomato pinworm, Tuta absoluta, led to an investigation of its natural mortality factors during the rainy season when the population level is low and during the dry season when population peaks occur. The aim of this study was to verify the seasonal variation in T. absoluta mortality factors in tomato crops. Immature stages of T. absoluta were obtained from laboratory‐rearing in the laboratory. These were taken to the field and monitored over two years. The mortality causes for each stage of insect development from egg to adult were assessed daily. Multiple biotic and abiotic mortality factors affected the immature T. absoluta stages such as rainfall, physiological disturbances, diseases, parasitoids and predators. The key T. absoluta mortality factor during summer–spring was predation. In addition, larvae predation correlated positively with temperature, wind velocity, photoperiod and rainfall. Nevertheless, during winter–fall, the key mortality factor was parasitism. Therefore, the critical stage for mortality was 3rd‐ and 4th‐instar larvae, being more vulnerable to natural control factors. Finally, the results showed the importance of vertical and horizontal action on natural mortality factors.     

Insect perception of ambient ultraviolet-B radiation

Solar ultraviolet‐B radiation (UV‐B, 290–315 nm) has a strong influence on the interactions between plants and animal consumers. Field studies in various ecosystems have shown that the intensity of insect herbivory increases when the UV‐B spectral band of solar radiation is experimentally attenuated using filters. This effect of UV‐B on insect herbivory has been attributed to UV‐B‐induced changes in the characteristics of plant tissues, and to direct damaging effects of UV‐B photons on the animals. We tested for effects of UV‐B radiation on insect behaviour using field experiments with the thrips Caliothrips phaseoli. When placed in a ‘choice’ tunnel under natural daylight, these insects showed a clear preference for low‐UV‐B environments, and this preference could not be accounted for by differences between environments in total irradiance. These results provide the first evidence of ambient UV‐B photoperception in an insect, challenging the idea that animals are unable to detect variations in the narrow UV‐B component of solar radiation.     

UV‐B impact on aphid performance mediated by plant quality and plant changes induced by aphids

Plants face various abiotic and biotic environmental factors and therefore need to adjust their phenotypic traits on several levels. UV‐B radiation is believed to impact herbivorous insects via host plant changes. Plant responses to abiotic challenges (UV‐B radiation) and their interaction with two aphid species were explored in a multifactor approach. Broccoli plants [Brassica oleracea L. convar. botrytis (L.), Brassicaceae] were grown in two differently covered greenhouses, transmitting either 80% (high UV‐B) or 4% (low UV‐B) of ambient UV‐B. Three‐week‐old plants were infested with either specialist cabbage aphids [Brevicoryne brassicae (L.), Sternorrhyncha, Aphididae] or generalist green peach aphids [Myzus persicae (Sulzer), Sternorrhyncha, Aphididae]. Plants grown under high‐UV‐B intensities were smaller and had higher flavonoid concentrations. Furthermore, these plants had reduced cuticular wax coverage, whereas amino acid concentrations of the phloem sap were little influenced by different UV‐B intensities. Cabbage aphids reproduced less on plants grown under high UV‐B than on plants grown under low UV‐B, whereas reproduction of green peach aphids in both plant light sources was equally poor. These results are likely related to the different specialisation‐dependent sensitivities of the two species. The aphids also affected plant chemistry. High numbers of cabbage aphid progeny on low‐UV‐B plants led to decreased indolyl glucosinolate concentrations. The induced change in these glucosinolates may depend on an infestation threshold. UV‐B radiation considerably impacts plant traits and subsequently affects specialist phloem‐feeding aphids, whereas aphid growth forces broccoli to generate specific defence responses.     

Influence of cornicle droplet secretions of the cabbage aphid,Brevicoryne brassicae,on parasitism behavior of na＇fve and experienced Diaeretiella rapae

Insects have evolved amazing methods of defense to ward off enemies. Many aphids release cornicle secretions when attacked by predators and parasitoids. These se cretions contain an alarm pheromone that alerts other colony members of danger, thereby providing indirect fitness benefits to the releaser. In addition, contact with cornicle se cretions could also threaten an attacker and could provide direct fitness to the releaser. However, cornicle secretions may also be recruited as a kairomonal cue by aphid natural enemies. In this study, we investigated the effect of the cornicle droplet volatiles of the cabbage aphid, Brevicoryne brassicae （L.）, on the hostsearching behavior of naive and experienced female Diaeretiella rapae （M＇Intosh） parasitoids in olfactometer studies. In addition, we evaluated the role ofB. brassicae cornicle droplets on the oviposition prefer ence of the parasitoid in a twochoice bioassay. Naive females did not exhibit any preference between volatiles from aphids secreting cornicle droplets over nonsecreting aphids, while experienced parasitoids exploited the secretions in their host location. Experienced females were also able to choose volatiles from both secreting and nonsecreting aphids over clean air, while this ability was not observed in naive females. Although secretion of cornicle droplets did not influence the percentage of first attack in either naive or experienced females, the success of attack （i.e. resulting in a larva） was significantly different between secreting and nonsecreting aphids in the case of experienced parasitoids.     

Natural enemy impacts on Bemisia tabaci (MEAM1) dominate plant quality effects in the cotton system

1. Plant quality (bottom‐up effects) and natural enemies (top‐down effects) affect herbivore performance. Furthermore, plant quality can also influence the impact of natural enemies. 2. Lower plant quality through reduced irrigation increased the abundance of the cryptic species from the Bemisia tabaci complex [hereafter B. tabaci Middle East Asia Minor 1 (MEAM1)], but not its natural enemies on cotton. It was therefore predicted that lower plant quality would diminish the impact of natural enemies in regulating this herbivore. 3. Over three cotton seasons, plant quality was manipulated via differential irrigation and natural enemy abundance with insecticides. Life tables were used to evaluate the impact of these factors on mortality of immature B. tabaci (MEAM1) over nine generations. 4. Mortality of B. tabaci (MEAM1) was consistently affected by natural enemies but not by plant quality. This pattern was driven by high levels of sucking predation, which was the primary (key) factor associated with changes in immature mortality across all irrigation and natural enemy treatments. Dislodgement (chewing predation and weather) and parasitism contributed as key factors in some cases. Analyses also showed that elimination of sucking predation and dislodgement would have the greatest effect on overall mortality. 5. The top‐down effects of natural enemies had dominant effects on populations of B. tabaci (MEAM1) relative to the bottom‐up effects of plant quality. Effects were primarily due to native generalist arthropod predators and not more host‐specific aphelinid parasitoids. The findings of this study demonstrate the important role of arthropod predators in population suppression and validate the importance of conservation biological control in this system for effective pest control.     

Quarantining behaviour of ants towards infected aphids as an antifungal mechanism in ant–aphid interactions

The ecological success of social insects, including ants, is tightly connected with their ability to protect themselves and their food resources. In exchange for energy‐rich honeydew, ants protect myrmecophilous aphids from various natural enemies. Fungal infection can have disastrous consequences for both mutualist partners, wherein aphids can be disease vectors. Behavioural responses towards fungus‐infected aphids of ant species in nature have scarcely been studied. Here, we studied the behaviour of honeydew foragers of four ant species – Formica polyctena Foerster, Formica rufa L., Formica pratensis Retzius (Hymenoptera: Formicidae, Formicini), and Lasius niger (L.) (Formicidae, Lasiini) – towards Symydobius oblongus (von Heyden) aphids contaminated with the generalist fungal pathogen Beauveria bassiana (Balsamo‐Crivelli) Vuillemin in the field. Aphid milkers from Formica spp. quickly detected and removed infected aphids from the host plant (Betula pendula Roth., Betulaceae). Neither ant species, the degree of aphid‐milker specialization (medium or high), nor the number of honeydew foragers had significant effects on the behaviour of Formica milkers towards infected aphids. Unlike Formica ants, L. niger usually displayed non‐aggressive behaviour (tolerance, antennation, honeydew collection, grooming). By the immediate removal of infected insects, Formica ants seem to minimize the probability of infection of symbionts as well as themselves. Quarantining behaviour may play an important role in ant–aphid interactions as a preventive antifungal mechanism formed under parasite pressure and thus contributing to the ecological success of ants.     

The effects of a plant defence priming compound, β-aminobutyric acid,on multitrophic interactions with an insect herbivore and a hymenopterous parasitoid

Biocontrol of aphids by natural enemies is utilized in many organic and integrated pest management schemes. β-aminobutyric acid (BABA), a non-protein amino acid, is a plant defence primer that suppresses growth of some insect herbivores when applied as a root drench. This investigation examined how applying BABA to host plants via the roots may impact on a parasitoid wasp of aphids. Female Aphidius ervi (Haliday) did not discriminate against pea aphids (Acyrthosiphon pisum (Harris)) reared on BABA-treated beans (Vicia faba L.) or show any modified responses to volatiles released from BABA-treated plants. BABA reduced the size of emerging wasps, primarily by inhibiting the growth of the host aphid. Metabolomic analysis revealed BABA in both aphids and emergent wasps indicating some potential for direct physiological inhibition to have occurred. Survival of the parasitoids was only reduced at doses of BABA likely to produce phytotoxic effects in many plant species, thus there may be potential to incorporate plant defence primers like BABA into integrated pest management practices. However, the precise mechanisms of BABA-inhibition of insects still require elucidation.     

Density and distribution of soybean aphid,Aphis glycines Matsumura (Hemiptera: Aphididae) in response to UV radiation

Increasing ultraviolet radiation (UV) has led to greater interest in its current and potential effects on organisms, including herbivorous insects. Here we report the short-term effects of UV on soybean aphids (Aphis glycines Matsumura), a common phytophagous pest of soybeans. We used two complementary approaches to examine how modifying UV radiation affects this phloem-feeding herbivore via changes to soybean aphid densities and their within plant distribution. We found that artificially adding UV in a lab setting decreased soybean aphid population size compared to a low UV control; however, blocking UV radiation in the field had minimal effects on aphid density. Further observations suggest that soybean aphid location could mediate UV effects; feeding on the underside of leaves may shield aphids from some harmful effects of UV. Our results demonstrate the potential importance of UV to insect herbivores and how behavior may influence such effects.     

Current status and future perspectives on natural enemies for pest control in Taiwan

ABSTRACT

In Taiwan, the agricultural policy, ‘Reduce the consumption of pesticide to half in the next 10 years’, was launched in 2017. Pesticide application, which results in contamination of food by chemical residues, pest resistance, and other adverse ecological effects, is a growing public and environmental concern. Pest control by natural predators is, thus, the best alternative. Biological control methods implemented based on insights obtained from studies on pest behaviour, rearing, and various crop management modes, increase the possibility of controlling pests in modern organic agricultural systems. More than a decade has passed since the first introduction of a predatory insect in Taiwan for pest control (in the 1990s). Predatory and parasitic natural enemies, including lacewing, predatory stink bugs, Orius, and parasitic wasps, were initially used for controlling thrips, aphids, spider mites, whiteflies, and lepidopteran pests. At present, there exists a wide range of integrated pest management (IPM) methods incorporating other non-chemical, biological, and agricultural methods. However, recently, there has been an increase in research and development on the utilisation of natural enemies of insects and the associated food safety issues. Mass production and release, storage, and handling techniques of insect predators and parasitoids have been successful in recent years. The final goal of present day research is to develop natural enemy products and provide an IPM-based model to farmers for using natural enemies in agricultural production systems, thereby reducing pesticide application and ensuring food security.     

Parasitoids induce production of the dispersal morph of the pea aphid, Acyrthosiphon pisum

In animals, inducible morphological defences against natural enemies mostly involve structures that are protective or make the individual invulnerable to future attack. In the majority of such examples, predators are the selecting agent while examples involving parasites are much less common. Aphids produce a winged dispersal morph under adverse conditions, such as crowding or poor plant quality. It has recently been demonstrated that pea aphids, Acyrthosiphon pisum, also produce winged offspring when exposed to predatory ladybirds, the first example of an enemy‐induced morphological change facilitating dispersal. We examined the response of A. pisum to another important natural enemy, the parasitoid Aphidius ervi, in two sets of experiments. In the first set of experiments, two aphid clones both produced the highest proportion of winged offspring when exposed as colonies on plants to parasitoid females. In all cases, aphids exposed to male parasitoids produced a higher mean proportion of winged offspring than controls, but not significantly so. Aphid disturbance by parasitoids was greatest in female treatments, much less in male treatments and least in controls, tending to match the pattern of winged offspring production. In a second set of experiments, directly parasitised aphids produced no greater proportion of winged offspring than unparasitised controls, thus being parasitised itself is not used by aphids for induction of the winged morph. The induction of wing development by parasitoids shows that host defences against parasites may also include an increased rate of dispersal away from infected habitats. While previous work has shown that parasitism suppresses wing development in parasitised individuals, our experiments are the first to demonstrate a more indirect influence of parasites on insect polyphenism. Because predators and parasites differ fundamentally in a variety of attributes, our finding suggests that the wing production in response to natural enemies is of general occurrence in A. pisum and, perhaps, in other aphids.