Parasitoids as taxonomists: how does the parasitoid Chouioia cunea distinguish between a host and a non-host?

BACKGROUND

How parasitoids distinguish hosts from non-hosts remains an unknown question. Chouioia cunea Yang (Eulophidae) is an important fall webworm parasitoid that attacks many forest and agricultural pests. To study the differences in the chemical clues used by C. cunea to distinguish host and non-host plants, we used gas chromatography-mass spectrometry (GC-MS) to identify volatile compounds of two C. cunea hosts (Hyphantria cunea and Helicoverpa armigera) and two non-hosts (Spodoptera exigua and Spodoptera frugiperda). Additionally, we used behavioral assays to compare the attraction of C. cunea to various compounds.

RESULTS

The two natural host species were more attractive than the two non-host species, in the following order: Hyphantria cunea > Helicoverpa armigera > S. exigua = S. frugiperda. The pupae of the natural hosts contained 1-dodecene, which was not produced by the two natural non-hosts. When the 'attractants' based on the difference between the species-specific blend emitted by pupae and the optimal blend were sprayed onto the natural non-host pupae, they significantly improved the attraction of C. cunea to the non-host pupae.

CONCLUSION

These results revealed that specific host-produced volatile compounds guide C. cunea to distinguish between natural hosts and non-hosts. Overall, this study provides a foundation for developing a behavior-modifying strategy to re-direct C. cunea attacks to control important non-host pests. © 2023 Society of Chemical Industry.

Lariophagus distinguendus (Hymenoptera: Pteromalidae) (Förster)-Past, Present, and Future: The History of a Biological Control Method Using L. distinguendus against Different Storage Pests

Legal requirements and consumer demands for residue-free products pose a big challenge for pest control in grain stores. One possible alternative to chemical insecticides is biological pest control with the pteromalid wasp Lariophagus distinguendus against the weevils Sitophilus granarius, S. oryzae (Coleoptera: Dryophtoridae), and many other storage pest beetles. The use of this wasp as a biocontrol agent was already suggested in 1919 by Prof. Dr. Hase [1]. Despite many studies on host-finding and behavioral biology, the applied aspect was neglected until 1994. Nowadays the wasps are commercially available and can now even be reared on-site, facilitating their use tremendously. This review highlights the milestones in L. distinguendus research, gives insights in current studies, and ventures a glimpse into the future.

Chemical cues from the coffee berry borer influence the locomotory behaviour of its bethylid parasitoids

Cephalonomia stephanoderis and Prorops nasuta are two bethylid wasps released into several Latin American countries for classical biological control of coffee berry borer, Hypothenemus hampei, the most serious insect pest of coffee worldwide. Recent studies on the host location behaviour of these parasitoids have shown that females of both species are attracted to volatile compounds released by immature stages and dust and frass of H. hampei. In this study, we investigated the role of the contact chemicals present in dust and frass of H. hampei on the behaviour of P. nasuta and C. stephanoderis females. Parasitoids remained longer on patches treated with methanol extracts than on acetone and hexane extracts. Females spent more time on the patch treated with the methanol extract of dust and frass than on the patches treated with the methanol extract of dry coffee and methanol control. The concentration of the methanol extracts from dust and frass influenced the locomotory activity of parasitoids of both species. The time that females spent in the patch tended to increase as the concentration of the methanol extracts increased. A further experiment aimed to identify other behavioural descriptors and gain a deeper understanding of the mechanisms underlying the response of parasitoids to methanol extracts was performed. Females of both species spent more time, covered more distance, turned more (per unit time and per unit distance), and decreased their speed when they contacted patches treated with methanol extracts in comparison to patches treated with methanol control.

Host habitat assessment by a parasitoid using fungal volatiles

BACKGROUND

The preference-performance hypothesis predicts that oviposition preference of insects should correlate with host suitability for offspring development. Therefore, insect females have to be able to assess not only the quality of a given host but also the environmental conditions of the respective host habitat. Chemical cues are a major source of information used by insects for this purpose. Primary infestation of stored grain by stored product pests often favors the intense growth of mold. This can lead to distinct sites of extreme environmental conditions (hot-spots) with increased insect mortality. We studied the influence of mold on chemical orientation, host recognition, and fitness of Lariophagus distinguendus, a parasitoid of beetle larvae developing in stored grain.

RESULTS

Volatiles of wheat infested by Aspergillus sydowii and A. versicolor repelled female parasitoids in an olfactometer. Foraging L. distinguendus females are known to be strongly attracted to the odor of larval host feces from the granary weevil Sitophilus granarius, which may adhere in remarkable amounts to the surface of the grains. Feces from moldy weevil cultures elicited neutral responses but parasitoids clearly avoided moldy feces when non-moldy feces were offered simultaneously. The common fungal volatile 1-octen-3-ol was the major component of the odor of larval feces from moldy weevil cultures and repelled female parasitoids at naturally occurring doses. In bioassays investigating host recognition behavior of L. distinguendus, females spent less time on grains containing hosts from moldy weevil cultures and showed less drumming and drilling behavior than on non-moldy controls. L. distinguendus had a clearly reduced fitness on hosts from moldy weevil cultures.

CONCLUSION

We conclude that L. distinguendus females use 1-octen-3-ol for host habitat assessment to avoid negative fitness consequences due to secondary mold infestation of host patches. The female response to fungal volatiles is innate, suggesting that host-associated fungi played a crucial role in the evolution of host finding strategies of L. distinguendus. Research on the role of host-associated microorganisms in the chemically mediated orientation of parasitoids is still at the beginning. We expect an increasing recognition of this issue in the future.

Sources of semiochemicals mediating host finding in Callosobruchus chinensis (Coleoptera: Bruchidae)

Bruchid pests such as Callosobruchus chinensis (Linnaeus) endanger stored legume seeds throughout the tropical belt. The chemical composition of the headspace volatiles from healthy and fourth instar larvae-infested cowpea seeds were identified, characterized, and compared using gas chromatography-mass spectrometry. Y-tube olfactometer bioassays were performed to evaluate the effect of these chemicals on the orientation of conspecific adult females. Analysis of volatiles released from healthy and infested seeds revealed qualitative differences for three out of the 17 compounds identified. Dimethyl disulphide, isobutenyl methyl ketone and methyl trisulphide were found only in the blend emitted from infested but not from healthy seeds. Quantitative differences were apparent for tridecane which was released in larger amounts from infested seeds. While volatiles collected from healthy seeds were attractive to female bruchids, volatiles collected from infested seeds were repellent. To test the hypothesis that the qualitative differences in the chemical composition found may be due to insect-derived components, the volatiles from frass and fourth instar larvae combined were analysed. These volatiles contained both of the sulphides emitted from infested seed but not from healthy seeds. Although a limited induction of volatiles from cowpea seeds cannot be excluded, it is postulated that behavioural differences of the female weevils are largely due to insect-derived semiochemicals. The potential use of such semiochemicals as part of an integrated pest management strategy is discussed.