Behaviour of male and female parasitoids in the field: influence of patch size,host density,and habitat complexity

1. Two field experiments were carried out to examine the role of patch size, host density, and complexity of the surrounding habitat, on the foraging behaviour of the parasitoid wasp Cotesia glomerata in the field. 2. First, released parasitoids were recaptured on patches of one or four Brassica nigra plants, each containing 10 hosts that were placed in a mown grassland area. Recaptures of females were higher than males, and males and females aggregated at patches with four plants. 3. In experiment 2, plants containing 0, 5 or 10 hosts were placed in unmown grassland plots that differed in plant species composition, on bare soil, and on mown grassland. Very low numbers of parasitoids were recaptured in the vegetated plots, while high numbers of parasitoids were recaptured on plants placed on bare soil or in mown grassland. Recaptures were higher on plants on bare soil than on mown grassland, and highest on plants containing 10 hosts. The host density effect was significantly more apparent in mown grassland than on bare soil. 4. Cotesia glomerata responds in an aggregative way to host density in the field. However, host location success is determined mostly by habitat characteristics, and stronger host or host‐plant cues are required when habitat complexity increases.     

Plant‐mediated indirect effects and the persistence of parasitoid–herbivore communities

We have examined the effects of herbivore diversity on parasitoid community persistence and stability, mediated by nonspecific information from herbivore‐infested plants. First, we investigated host location and patch time allocation in the parasitoid Cotesia glomerata in environments where host and/or nonhost herbivores were present on Brassica oleracea leaves. Parasitoids were attracted by infochemicals from leaves containing nonhost herbivores. They spent considerable amounts of time on such leaves. Thus, when information from the plant is indistinct, herbivore diversity is likely to weaken interaction strengths between parasitoids and hosts. In four B. oleracea fields, all plants contained herbivores, often two or more species. We modelled parasitoid–herbivore communities increasing in complexity, based on our experiments and field data. Increasing herbivore diversity promoted the persistence of parasitoid communities. However, at a higher threshold of herbivore diversity, parasitoids became extinct due to insufficient parasitism rates. Thus, diversity can potentially drive both persistence and extinctions.     

Herbivore species identity rather than diversity of the non‐host community determines foraging behaviour of the parasitoid wasp Cotesia glomerata

Extensive research has been conducted to reveal how species diversity affects ecosystem functions and services. Yet, consequences of diversity loss for ecosystems as a whole as well as for single community members are still difficult to predict. Arthropod communities typically are species‐rich, and their species interactions, such as those between herbivores and their predators or parasitoids, may be particularly sensitive to changes in community composition. Parasitoids forage for herbivorous hosts by using herbivore‐induced plant volatiles (indirect cues) and cues produced by their host (direct cues). However, in addition to hosts, non‐suitable herbivores are present in a parasitoid's environment which may complicate the foraging process for the parasitoid. Therefore, ecosystem changes in the diversity of herbivores may affect the foraging efficiency of parasitoids. The effect of herbivore diversity may be mediated by either species numbers per se, by specific species traits, or by both. To investigate how diversity and identity of non‐host herbivores influence the behaviour of parasitoids, we created environments with different levels of non‐host diversity. On individual plants in these environments, we complemented host herbivores with 1–4 non‐host herbivore species. We subsequently studied the behaviour of the gregarious endoparasitoid Cotesia glomerata L. (Hymenoptera: Braconidae) while foraging for its gregarious host Pieris brassicae L. (Lepidoptera: Pieridae). Neither non‐host species diversity nor non‐host identity influenced the preference of the parasitoid for herbivore‐infested plants. However, after landing on the plant, non‐host species identity did affect parasitoid behaviour, whereas non‐host diversity did not. One of the non‐host species, Trichoplusia ni Hübner (Lepidoptera: Noctuidae), reduced the time the parasitoid spent on the plant as well as the number of hosts it parasitized. We conclude that non‐host herbivore species identity has a larger influence on C. glomerata foraging behaviour than non‐host species diversity. Our study shows the importance of species identity over species diversity in a multitrophic interaction of plants, herbivores, and parasitoids.     

Male and female Trybliographa rapae (Hymenoptera: Figitidae) behavioural responses to food plant, infested host plant and combined volatiles

Many parasitoids use volatiles produced by plants as important cues during their food and host search process. We investigated the attraction of the parasitic wasp Trybliographa rapae Westwood (Hymenoptera: Figitidae) to volatiles emitted from plants infested by the cabbage root fly Delia radicum L. (Diptera: Anthomyiidae), as well as to volatiles from a nectar food plant. Behavioural choice tests showed that male parasitoids were not attracted to any volatiles from plants infested by D. radicum or from nectar plants, while females showed clear attraction to both volatile sources. Young females were more attracted to combined volatiles of host and food plants over those from only the host plant, whereas older females showed no differences in attraction to the two odour sources. This suggests that intercropping attractive flowers with host plants could potentially be used to recruit newly emerged parasitoids from surrounding fields while older parasitoids invest more energy in host location than in additional food search. Volatiles from a whole infested plant were chosen over those emitted from separated above- and below-ground parts from infested plants. It is important to consider the availability of both energy and host resources for parasitoids when designing an eco-compatible management of a vegetable crop system.     

The role of herbivore‐ and plant‐related experiences in intraspecific host preference of a relatively specialized parasitoid

Parasitoids use odor cues from infested plants and herbivore hosts to locate their hosts. Specialist parasitoids of generalist herbivores are predicted to rely more on herbivorederived cues than plant-derived cues. Microplitis croceipes (Cresson)(Hymenoptera: Braconidae) is a relatively specialized larval endoparasitoid of Heliothis virescens (F.)(Lepidoptera: Noctuidae), which is a generalist herbivore on several crops including cotton and soybean. Using M. croceipes/H. virescens as a model system, we tested the following predictions about specialist parasitoids of generalist herbivores:(i) naive parasitoids will show innate responses to herbivore-emitted kairomones, regardless of host plant identity and (ii) herbivore-related experience will have a greater influence on intraspecific oviposition preference than plant-related experience. Inexperienced (naive) female M. croceipes did not discriminate between cotton-fed and soybean-fed H. virescens in oviposition choice tests, supporting our first prediction. Oviposition experience alone with either host group influenced subsequent oviposition preference while experience with infested plants alone did not elicit preference in M. croceipes, supporting our second prediction. Furthermore, associative learning of oviposition with host-damaged plants facilitated host location. I terestingly, naive parasitoids attacked more soybeathan cotton-fed host larvae in two-choice tests when a background of host-infested cotton odor was supplied, and vice versa. This suggests that plant volatiles may have created an olfactory contrast effect. We discussed ecological significance of the results and concluded that both plant- and herbivore-related experiences play important role in parasitoid host foraging.     

Host‐searching responses to herbivory‐associated chemical information and patch use depend on mating status of female solitary parasitoid wasps

1. In a tritrophic interaction system consisting of plants, herbivores, and their parasitoids, chemicals released from plants after herbivory are known to play important roles for many female parasitoids to find their hosts efficiently. On the plant side, chemical information associated with herbivory can act as an indirect defence by attracting the natural enemies of the host herbivores. 2. However, mated and virgin females of haplodiploid parasitoids might not necessarily respond to such chemical cues in the same way. Since virgin females can produce only sons, they might refrain from searching for hosts to invest eggs until copulation, in order to produce both sexes. 3. Here, we investigated differential host‐searching behaviours shown by mated and virgin females in the solitary parasitoid wasp, Cotesia vestalis, in response to herbivory‐associated chemical information from cruciferous plants infested by their host larvae, Plutella xylostella. 4. Mated females showed a significantly higher flight preference for host‐infested plants over intact plants, while no preference was observed with virgin females. Mated females also showed more intensive antennal searching and ovipositor probing behaviours to leaf squares with wounds caused by hosts than did virgin females. Furthermore, mated females stayed longer in host patches with higher parasitism rates than virgin females. 5. These results indicate that mating status of C. vestalis females clearly influences their host‐searching behaviour in response to herbivory‐associated chemical information and patch exploitation. Female parasitoids seem to forage for hosts depending on their own physiological condition in a tritrophic system.     

Role of volatile semiochemicals in host location by the egg parasitoid Anagrus breviphragma

Recent investigations conducted on several tritrophic systems have demonstrated that egg parasitoids, when searching for host eggs, may exploit plant synomones that have been induced as a consequence of host oviposition. In this article we show that, in a system characterized by host eggs embedded in the plant tissue, naïve females of the egg parasitoid Anagrus breviphragma Soyka (Hymenoptera: Mymaridae) responded in a Y‐tube olfactometer to volatiles from leaves of Carex riparia Curtis (Cyperaceae) containing eggs of one of its hosts, Cicadella viridis (L.) (Hemiptera: Cicadellidae). The wasp did not respond to host eggs or to clean leaves from non‐infested plants compared with clean air, whereas it showed a strong preference for the olfactometer arm containing volatiles of leaves with embedded host eggs, compared with the arm containing volatiles of leaves from a non‐infested plant or host eggs extracted from the plant. When the eggs were removed from an infested leaf, the parasitoid preference was observed only if eggs were added aside, suggesting a synergistic effect of a local plant synomone and an egg kairomone. The parasitoid also responded to clean leaves from an egg‐infested plant when compared with leaves from a non‐infested plant, indicating a systemic effect of volatile induction.     

Arboreal Ant Abundance and Leaf Miner Damage in Coffee Agroecosystems in Mexico

Shaded coffee agroecosystems traditionally have few pest problems potentially due to higher abundance and diversity of predators of herbivores. However, with coffee intensification (e.g., shade tree removal or pruning), some pest problems increase. For example, coffee leaf miner outbreaks have been linked to more intensive management and increased use of agrochemicals. Parasitic wasps control the coffee leaf miner, but few studies have examined the role of predators, such as ants, that are abundant and diverse in coffee plantations. Here, we examine linkages between arboreal ant communities and coffee leaf miner incidence in a coffee plantation in Mexico. We examined relationships between incidence and severity of leaf miner attack and: (1) variation in canopy cover, tree density, tree diversity, and relative abundance of Inga spp. shade trees; (2) presence of Azteca instabilis, an arboreal canopy dominant ant; and (3) the number of arboreal twig‐nesting ant species and nests in coffee plants. Differences in vegetation characteristics in study plots did not correlate with leaf miner damage perhaps because environmental factors act on pest populations at a larger spatial scale. Further, presence of A. instabilis did not influence presence or severity of leaf miner damage. The proportion of leaves with leaf miner damage was significantly lower where abundance of twig‐nesting ants was higher but not where twig‐nesting ant richness was higher. These results indicate that abundance of twig‐nesting ants in shaded coffee plantations may contribute to maintenance of low leaf miner populations and that ants provide important ecosystem services in coffee agroecosystems.     

Density‐mediated indirect interactions alter host foraging behaviour of parasitoids without altering foraging efficiency

1. Foraging decisions of parasitoids are influenced by host density via density‐mediated indirect interactions. However, in the parasitoid's environment, non‐suitable herbivores are also present. These non‐hosts also occur in different densities, which can affect a parasitoid's foraging behaviour. 2. The influence of non‐host densities can be expressed during the first phase of the foraging process, when parasitoids use plant volatiles to locate plants infested by their host. They may also play a role during the second phase, when parasitoids use infochemicals from the host and plant to locate, recognise and accept the host. 3. By using laboratory and field setups, it was studied whether the density of non‐host herbivores influences these two phases of the foraging behaviour of the parasitoid Cotesia glomerata as well as the parasitoid's efficiency to find its host, Pieris brassicae caterpillars. 4. The findings show that a high non‐host density, regardless of the species used, negatively affected parasitoid preference for host‐infested plants, but that the behaviour on the plant and the total host‐finding efficiency of the parasitoids were not influenced by non‐host density. 5. These results are discussed in the context of density‐mediated indirect interactions.     

Effects of quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested maize on the attraction of the larval parasitoid Cotesia kariyai

Cotesia kariyai Watanabe (Hymenoptera: Braconidae) is a specialist larval parasitoid of Mythimna separata Walker (Lepidoptera: Noctuidae). Cotesia kariyai wasps use herbivore‐induced plant volatiles (HIPVs) to locate hosts. However, complex natural habitats are full of volatiles released by both herbivorous host‐ and non‐host‐infested plants at various levels of intensity. Therefore, the presence of non‐hosts may affect parasitoid decisions while foraging. Here, the host‐finding efficiency of naive C. kariyai from HIPVs influenced by host‐ and non‐host‐infested maize [Zea mays L. (Poaceae)] plants was investigated with a four‐arm olfactometer. Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) was selected as a non‐host species. One unit (1 U) of host‐ or non‐host‐infested plant was prepared by infesting a potted plant with five host or seven non‐host larvae. In two‐choice bioassays, host‐infested plants fed upon by different numbers of larvae, and various units of host‐ and non‐host‐infested plants (infestation units; 1 U, 2 U, and 3 U) were arranged to examine the effects of differences in volatile quantity and quality on the olfactory responses of C. kariyai with the assumption that volatile quantity and quality changes with differences in numbers of insects and plants. Cotesia kariyai was found to perceive quantitative differences in volatiles from host‐infested plants, preferring larger quantities of volatiles from larger numbers of larvae or plants. Also, the parasitoids discriminated between healthy plants, host‐infested plants, and non‐host‐infested plants by recognising volatiles released from those plants. Cotesia kariyai showed a reduced preference for host‐induced volatiles, when larger numbers of non‐host‐infested plants were present. Therefore, quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested plants appear to affect the decision of C. kariyai during host‐habitat searching in multiple tritrophic systems.     

Elevational turnover in the composition of leaf miners and their interactions with host plants in Australian subtropical rainforest

Leaf miners are specialist herbivorous insects that are potentially vulnerable to environmental change because of their dependency on particular host plants. Little, however, is known about how climate affects the distribution of leaf miner communities and their interactions with host plants. Elevational gradients are useful tools for understanding how ecological communities respond to local clines in climate. Given that plant communities are known to undergo elevational turnover in response to changes in climatic conditions, we expect that leaf miner species will also change with elevation. We repeatedly hand collected leaf miners along three elevational gradients in subtropical rainforest in eastern Australia. Individual leaf miners were counted and identified to species, and their host plants were recorded. We tested if leaf miner species richness and the number of unique interactions among leaf miner and host plant species were affected by elevation. We also tested if the composition of leaf miner species and the composition of interactions between leaf miners and host plants showed a relationship with elevation. The rarefied number of unique leaf miner–host plant interactions significantly decreased with elevation, with a slight peak at approx. 700 m a.s.l., while neither rarefied or observed species richness (species density) of leaf miners nor observed numbers of unique interactions (interaction density) were significantly affected by elevation. The composition of leaf miner species and the composition of leaf miner–host plant interactions (occurrence of pairwise interactions) were significantly related to elevation. Elevational turnover in leaf miner species composition indicated that different species varied in their response to changes in biotic and/or abiotic conditions imposed by increasing elevation. Through our analyses, we identified four leaf miner species that may be locally vulnerable to climate change, as a result of their restricted elevational distribution and level of host specificity.     

Physical barriers and corridors in urban habitats affect colonisation and parasitism rates of a specialist leaf miner

1. Urban environments are fragmented habitats characterised by the presence of physical barriers, which may negatively affect dispersal and colonisation by insect herbivores and their natural enemies. Conversely, plants growing along pavements may function as dispersal corridors, helping to moderate the harmful effects of resource patch isolation on organism movement and population persistence. 2. We experimentally tested the effects of walls as physical barriers to the dispersal of the leaf miner Liriomyza commelinae Frost and colonisation of its host plant, Commelina erecta L., in urban habitats. We also evaluated whether plants along pavements could act as corridors for this species. 3. We exposed experimental host plants to the leaf miner in houses with front gardens and back yards, the latter being completely surrounded by walls. The front gardens had walls but none separating them from the pavement. Previously mined plants were also exposed to parasitoids in the yards to determine parasitoid attack. 4. Liriomyza commelinae took longer to colonise back yards with higher walls, and the abundance of mined plants along pavements reduced the colonisation time. Leaf‐miner abundance was marginally affected by the yard type, and was lower in back yards. Cumulative parasitism rates decreased with increasing distance at which mined plants were placed from pavements. 5. Constructions act as physical barriers, having a negative impact on colonisation of host plants by leaf miners. The function of pavements as corridors seems to depend on the abundance of mined plants. Parasitism may be affected by distance from the corridor rather than physical barriers or other potential hosts.     

Plant diversity has contrasting effects on herbivore and parasitoid abundance in Centaurea jacea flower heads

High biodiversity is known to increase many ecosystem functions, but studies investigating biodiversity effects have more rarely looked at multi‐trophic interactions. We studied a tri‐trophic system composed of Centaurea jacea (brown knapweed), its flower head‐infesting tephritid fruit flies and their hymenopteran parasitoids, in a grassland biodiversity experiment. We aimed to disentangle the importance of direct effects of plant diversity (through changes in apparency and resource availability) from indirect effects (mediated by host plant quality and performance). To do this, we compared insect communities in C. jacea transplants, whose growth was influenced by the surrounding plant communities (and where direct and indirect effects can occur), with potted C. jacea plants, which do not compete with the surrounding plant community (and where only direct effects are possible). Tephritid infestation rate and insect load, mainly of the dominant species Chaetorellia jaceae, decreased with increasing plant species and functional group richness. These effects were not seen in the potted plants and are therefore likely to be mediated by changes in host plant performance and quality. Parasitism rates, mainly of the abundant chalcid wasps Eurytoma compressa and Pteromalus albipennis, increased with plant species or functional group richness in both transplants and potted plants, suggesting that direct effects of plant diversity are most important. The differential effects in transplants and potted plants emphasize the importance of plant‐mediated direct and indirect effects for trophic interactions at the community level. The findings also show how plant–plant interactions critically affect results obtained using transplants. More generally, our results indicate that plant biodiversity affects the abundance of higher trophic levels through a variety of different mechanisms.     

Intraspecific variation in herbivore‐induced plant volatiles influences the spatial range of plant–parasitoid interactions

Chemical information influences the behaviour of many animals, thus affecting species interactions. Many animals forage for resources that are heterogeneously distributed in space and time, and have evolved foraging behaviour that utilizes information related to these resources. Herbivore‐induced plant volatiles (HIPVs), emitted by plants upon herbivore attack, provide information on herbivory to various animal species, including parasitoids. Little is known about the spatial scale at which plants attract parasitoids via HIPVs under field conditions and how intraspecific variation in HIPV emission affects this spatial scale. Here, we investigated the spatial scale of parasitoid attraction to two cabbage accessions that differ in relative preference of the parasitoid Cotesia glomerata when plants were damaged by Pieris brassicae caterpillars. Parasitoids were released in a field experiment with plants at distances of up to 60 m from the release site using intervals between plants of 10 or 20 m to assess parasitism rates over time and distance. Additionally, we observed host‐location behaviour of parasitoids in detail in a semi‐field tent experiment with plant spacing up to 8 m. Plant accession strongly affected successful host location in field set‐ups with 10 or 20 m intervals between plants. In the semi‐field set‐up, plant finding success by parasitoids decreased with increasing plant spacing, differed between plant accessions, and was higher for host‐infested plants than for uninfested plants. We demonstrate that parasitoids can be attracted to herbivore‐infested plants over large distances (10 m or 20 m) in the field, and that stronger plant attractiveness via HIPVs increases this distance (up to at least 20 m). Our study indicates that variation in plant traits can affect attraction distance, movement patterns of parasitoids, and ultimately spatial patterns of plant–insect interactions. It is therefore important to consider plant‐trait variation in HIPVs when studying animal foraging behaviour and multi‐trophic interactions in a spatial context.     

Diamondback moth females oviposit more on plants infested by non‐parasitised than by parasitised conspecifics

Abstract 1. When offered a choice, female diamondback moths (Plutella xylostella) oviposited more eggs on plants with non‐parasitised conspecific larvae than on plants with parasitised larvae. 2. The leaf area consumed by parasitised larvae was significantly lower than that by non‐parasitised larvae. However, this quantitative difference in larval damage did not explain the female’s ability to discriminate between plants with parasitised and non‐parasitised larvae, as females showed an equal oviposition preference for plants infested by higher or lower densities of non‐parasitised larvae. 3. Pupal weight and duration of the larval stage of P. xylostella were independent of whether larvae were reared on plants that were previously infested by either non‐parasitised or parasitised larvae. 4. The larval parasitoid Cotesia vestalis did not distinguish between plants infested by non‐parasitised larvae and plants infested by larvae that had already been parasitised by conspecific wasps. 5. Based on these data, it can be concluded that the moth oviposition preference for plants infested by non‐parasitised conspecifics relative to plants infested by parasitised conspecifics was not explained by plant quality or by the attractiveness of plants towards wasps. It is hypothesised that one of the reasons for this preference is avoidance of plants where a relatively high risk of parasitism is expected due to the emergence of parasitoids from the parasitised host larvae.     

Aboveground herbivory affects indirect defences of brassicaceous plants against the root feeder Delia radicum Linnaeus: laboratory and field evidence

1. Belowground herbivory has recently been shown to disrupt the host location behaviour of aboveground parasitoids and thereby impact plants indirect defences. Reverse interactions, on the other hand, have received little attention so far. 2. Lab and field studies were conducted to examine whether the presence of the leaf herbivore Pieris brassicae Linnaeus on brassicaceous plants influences the response of Trybliographa rapae Westwood, a specialist parasitoid of the root feeder Delia radicum Linnaeus. 3. The present results show that the attraction of the parasitoid towards host‐infested plants disappeared when these plants were also infested by P. brassicae. This absence of attraction was observed both when the complete odour blend or only undamaged leaves from damaged plants were offered, emphasising the role of systemically induced volatiles for host location in T. rapae. 4. Furthermore, the field study revealed that parasitism levels dropped from 30% on root‐infested plants to 4% on double‐infested plants. 5. The present study is the first to confirm that reduced attraction to host‐infested plants as a result of simultaneous attack by below‐ and aboveground herbivores translates into lower levels of parasitism in the field.     

Attraction of the specialist parasitoid Cotesia rubecula to Arabidopsis thaliana infested by host or non-host herbivore species

In this study we investigated whether in a two‐choice set‐up the parasitoid Cotesia rubecula (Marshall) (Hymenoptera, Braconidae) distinguishes between volatiles emitted by Arabidopsis thaliana (L.) Heynh. (Brassicaceae) infested with its host, Pieris rapae (L.) (Lepidoptera: Pieridae) and Arabidopsis infested with non‐host herbivores. Four non‐host herbivore species were tested: the caterpillars Plutella xylostella (L.) (Lepidoptera: Plutellidae) and Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), both chewing insects, the spider mite Tetranychus urticae (Koch) (Acari: Tetranychidae), which punctures parenchymal cells, and the aphid Myzus persicae (Sulzer) (Hemiptera: Aphidoidea), which is a phloem‐feeder. Compared with undamaged plants, C. rubecula females were more attracted to Arabidopsis plants infested by P. rapae, P. xylostella, S. exigua, or T. urticae, but not to plants infested by M. persicae. The parasitoids preferred host‐infested plants to spider mite‐ or aphid‐infested plants, but not to plants infested with non‐host caterpillars (P. xylostella or S. exigua). The data show that when Arabidopsis plants are infested with a leaf tissue‐damaging herbivore they emit a volatile blend that attracts C. rubecula females and the wasps only discriminate between a host and non‐host herbivore when the type of damage is different (chewing vs. piercing). When Arabidopsis is infested with a herbivore that hardly damages leaf tissue, C. rubecula females are not attracted. These results may be explained by differences in the amount of damage and in the relative importance of different signal‐transduction pathways induced by different types of herbivores.     

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.     

Species richness and abundance of native leaf miners are affected by the presence of the invasive horse-chestnut leaf miner

The effect of the alien horse-chestnut leaf miner, Cameraria ohridella, on native fauna was studied by comparing the species richness of native leaf miner communities and the abundance of selected native leaf miner species in the presence and absence of horse-chestnut trees infested by C. ohridella, in various environments in Europe. The species richness of native leaf miner communities in Switzerland was lower at sites where C. ohridella was present than at control sites. In Switzerland, France and Bulgaria, several native leaf miner species were significantly less abundant in the vicinity of infested horse-chestnuts. The native species most affected by the presence of the invasive alien species were those occurring early in the year and sharing their parasitoid complex with C. ohridella. These results suggest apparent competition mediated by shared natural enemies because these are the only link between C. ohridella and native leaf miners using other food resources.     

Adult experience modifies attraction of the leafminer parasitoidOpius dissitus (Hymenoptera: Braconidae) to volatile semiochemicals

Oviposition-experienced females of Opius dissitus Muesebeck, a braconid parasitoid of Liriomyza sativaeBlanchard, preferentially landed on leafminer-infested rather than uninfested lima bean (Phaseolus lunatus L.) plants in a flight tunnel assay. Both naive and oviposition-experiencedparasitoids responded strongly to odors of infested lima bean plants in a four-arm olfactometer in comparison with odors of uninfested plants, suggesting that volatile semiochemicals are used in host location. Parasitoids with an oviposition experience on lima bean (lima-experienced) spent significantly more time in the infested odor than naive individuals, however, eggplant-experienced wasps did not spend significantly more time in the infested odor field than naive wasps. When parasitoids reared on leafminers in lima bean were provided a choice between the odor of infested lima bean and the odor of infested eggplant or cotton, naive and lima-experienced wasps preferred infested lima odor. An oviposition experience on the other plant species resulted in a dramatic shift in preference. It was concluded that the experience effect was due, at least in part, to associative learning, as has been reported for other parasitoids. The parasitoids may perceive unconditioned stimuli during host contact and oviposition on an infested leaf and may associate those stimuli with volatile semiochemicals emanating from the leaf or host. Subsequently, the volatiles associated with the presence of hosts are used in directing the search for hosts.