Foraging efficiency and outcomes of interactions of two pupal parasitoids attacking the invasive spotted wing drosophila

The role of biodiversity in the delivery of ecosystem services is increasingly being studied by trait-based functional approaches. Here, we review and discuss the contribution of a trait-based approach to understanding plant–arthropod interactions and improving conservation biological control. The stable biological control of multispecies herbivore communities requires functional diversity and a redundancy of natural enemies, including specialists and generalists, with minimal antagonistic interactions. The management of arthropod communities through plant community requires the plant community to perform several functions, including the provision of diversified trophic resources and appropriate physical habitats. Many studies have investigated the ability of plants to provide these functions, but many of the results obtained were limited to single species. The description of communities in terms of traits underlying trophic and non-trophic interactions between plants and animals would make it possible to extrapolate findings to other species. Studies on plant–herbivore and plant–pollinator interactions have identified several traits as important for trophic resource provision, in terms of resource quantity, accessibility, quality and temporal availability. By contrast, traits relating to physical habitat provision and microclimate modification have been little explored. Several metrics describing the functional composition and diversity of communities have been proposed, to extend the trait-based approach to plant community level, but the extent to which multitrophic communities are affected by plant traits remains largely unexplored. The next step will be to identify the combinations of these plant community metrics best explaining their impact on arthropod communities and disentangling the roles of plant functional composition and diversity.

https://hal-univ-avignon.archives-ouvertes.fr/hal-01778315/document

Understanding plant–arthropod interactions in multitrophic communities to improve conservation biological control: useful traits and metrics

Habitat use by crop pests and natural enemies in a Mediterranean vineyard agroecosystem

Potential competitive outcomes among three solitary larval endoparasitoids as candidate agents for classical biological control of Drosophila suzukii

1. Pests, pesticides and biological control 2. Natural enemies 3. Biological control ecology 4. Early naturalists and experiments 5. The first foreign explorers 6. Modern foreign exploration and successes 7. Maximising biological control through research 8. Utilization by the public 9. Other biological methods 10. Escape from the pesticide dilemma.

Biological Control by Natural Enemies

Epiphyas postvittana (Walker, 1863), or light brown apple moth (LBAM), is a highly polyphagous native Australian species and a major insect pest in Australian vineyards. Dolichogenidea tasmanica (Cameron, 1912) is the most abundant parasitoid of the larval stages of LBAM. The prime objective of our study was to determine the parasitism success of D. tasmanica on different larval stages of E. postvittana. Additionally, we aimed to find out if larval head capsule width could be used to determine the instar number by examining the variability in head capsule size of each instar of LBAM and the effect of rearing temperature on larval head capsule size. To determine which of the first three larval stages of LBAM parasitised is most effectively by D. tasmanica, choice and no-choice tests were conducted in a wind tunnel. Head capsule widths varied with rearing temperature, especially in the final fifth or sixth instar. We showed that the ranges of head capsule widths overlaps between successive instars three through six, which makes it impossible to distinguish these instars of LBAM using head capsule size alone. We showed that first, second and third instars of LBAM are parasitised by D. tasmanica. No-choice and choice tests revealed that there are significant differences in parasitism among the three susceptible instars, with the highest percentage of parasitism found in second instars in no-choice and choice tests (65.1% and 65.8%, respectively) compared with first instars (61.1% and 45.1%) and third instars (27.3% and 37.5%). Wasps developed faster in third instars, but the wasp female's size was not significantly different among the instars attacked. These data confirm that D. tasmanica is capable of parasitising early larval instars, which is important for minimising damage through biological control.

Host stage preference of Dolichogenidea tasmanica (Cameron, 1912) (Hymenoptera: Braconidae), a parasitoid of Epiphyas postvittana (Walker, 1863) (Lepidoptera: Tortricidae)

Non-crop habitat adjacent to crops may be important for enhancing the activity of natural enemies in crops. However, it is not always clear whether natural enemies that are active in non-crop habitats actually contribute to pest suppression in adjacent crop habitats. We hypothesised that parasitic wasps that utilise the same hosts can be segregated between crop and non-crop habitats in an agro-ecosystem. We tested this hypothesis using the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), in vineyards and adjacent native vegetation. We experimentally measured the parasitism rate of larval E. postvittana at six and eight sites in both vineyards and the adjacent native vegetation in two consecutive years. Wild larval Tortricidae were also collected at each experimental site to assess their diversity and related parasitoids. Parasitised hosts were then identified using a PCR-based protocol to examine the parasitoids’ host ranges. The parasitoid Therophilus unimaculatus (Turner) (Hymenoptera: Braconidae) was most active in non-crop native vegetation, whereas Dolichogenidea tasmanica (Cameron) (Hymenoptera: Braconidae) parasitised the most larvae in vineyards. Parasitism of E. postvittana by D. tasmanica was higher on grape than on plantain, which indicates that host plants influence activities in different habitat. Both species shared the same range of tortricid hosts. Overall, our results indicate the two key parasitoids that attack E. postvittana differ in their pattern of habitat use. The native vegetation adjacent to crops may not enhance the activity of some natural enemies for pest control in an agricultural ecosystem.

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The activities of generalist parasitoids can be segregated between crop and adjacent non-crop habitats

Two generalist parasitoids, Dolichogenidea tasmanica (Cameron) (Hymenoptera: Braconidae) and Therophilus unimaculatus (Turner) (Hymenoptera: Braconidae) attack early instars of tortricid moths, including the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae). The two parasitoids co-exist in natural habitats, while D. tasmanica is dominant in vineyards, whereas T. unimaculatus occurs mainly in adjacent native vegetation. This difference suggests possible competition between the two species, mediated by habitat. Here, we report on the extent of interspecific differences in host discrimination and the outcome of interspecific competition between the two parasitoids. The parasitoids did not show different behavioural responses to un-parasitized hosts or those that were parasitized by the other species. Larvae of D. tasmanica out-competed those of T. unimaculatus, irrespective of the order or interval between attacks by the two species. The host larvae that were attacked by two parasitoids died more frequently before a parasitoid completed its larval development than those that were attacked by a single parasitoid. Dissection of host larvae parasitized by both species indicated that first instars of D. tasmanica attacked and killed larval T. unimaculatus.

Interspecific competition between two generalist parasitoids that attack the leafroller Epiphyas postvittana (Lepidoptera: Tortricidae).

The light brown apple moth, Epiphyas postvittana is a key pest of wine grapes in Australia. Two parasitoids, Dolichogenidea tasmanica and Therophilus unimaculatus, attack the larval stage of this pest. D. tasmanica is dominant in vineyards, whereas T. unimaculatus is mainly active in native vegetation. We sought to understand why they differ in their use of habitats. Plants are a major component of habitats of parasitoids, and herbivore-infested plants influence parasitoid foraging efficiency by their architecture and emission of volatile chemicals. We investigated how different plant species infested by E. postvittana could affect the foraging success of the two parasitoid species in both laboratory and field experiments. Four common host-plant species were selected for this study. In paired-choice experiments to determine the innate foraging preferences for plants, both parasitoid species showed differences in innate search preferences among plant species. The plant preference of D. tasmanica was altered by oviposition experience with hosts that were feeding on other plant species. In a behavioral assay, the two parasitoid species allocated their times engaged in various types of behavior differently when foraging on different plant species. For both parasitoids, parasitism on Hardenbergia violacea was the highest of the four plant species. Significantly more larvae dropped from Myoporum insulare when attacked than from the other three host-plant species, which indicates that parasitism is also affected by interactions between plants and host insects. In vineyards, parasitism by D. tasmanica was significantly lower on M. insulare than on the other three host-plant species, but the parasitism rates were similar among the other three plant species. Our results indicate that plants play a role in the habitat preferences of these two parasitoid species by influencing their foraging behavior, and are likely to contribute to their distributions among habitats.

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Yi Feng

Papers

Host stage preference of Dolichogenidea tasmanica (Cameron, 1912) (Hymenoptera: Braconidae), a parasitoid of Epiphyas postvittana (Walker, 1863) (Lepidoptera: Tortricidae)

The activities of generalist parasitoids can be segregated between crop and adjacent non-crop habitats

Interspecific competition between two generalist parasitoids that attack the leafroller Epiphyas postvittana (Lepidoptera: Tortricidae).

Host plants affect the foraging success of two parasitoids that attack light brown apple moth Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae)