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Impact of the exotic fall armyworm on larval parasitoids associated with the lepidopteran maize stemborers in Kenya

Exotic invasive insect herbivores have the potential to interfere with existing herbivores-natural enemies’ interactions in new environments. Understanding the acceptability and suitability of a new invasive pest such as Fall Armyworm (FAW), Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae) to the existing parasitoids-maize stemborers interactions is the first step in elucidating the impact that this exotic pest can have on the existing natural enemies used in biological control of maize stemborers in Kenya. The most commonly used larval parasitoids to biocontrol maize stemborer communities in Kenya are Cotesia flavipes Cameron (Hymenoptera: Braconidae) and two populations of the native Cotesia sesamiae Cameron (Hymenoptera: Braconidae). The acceptability and host preference were carried out and the parasitized larvae were followed up for their development until they formed cocoon, died or formed pupae. The odour preference was studied in Y-tube olfactometer assays. The results showed that all these parasitoids species have significantly  attacked FAW larvae but none yielded offspring though they induced high nonreproductive host mortality when compared to natural mortality. Furthermore, the parasitoid that inserted their ovipositor into FAW larvae exhibited similar acceptance between larvae of FAW and their respective stemborer hosts under dual-choice bioassays. In olfactometric bioassays, the parasitoids were more attracted to plants infested by FAW than uninfested plants and even a marked preference to the odours of plants infested by FAW over that of plants infested by their natural host counterparts. This study illustrates that exotic pest, such as FAW, can impact existing stemborer-parasitoid’ interactions associated with Zea mays, even if it cannot be used as host by parasitoids associated with these stemborers. Although additional studies are needed, FAW might therefore have a negative impact on stemborer biological control already established before its invasion.

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Roger Day
Roger Day (@roger-day)
29 days ago

This is interesting! Does anyone else have examples of how natural enemy mortality of FAW might affect natural enemy mortality to other hosts?

When the parasitoids inserted their ovipositors in FAW, how often do they oviposit? If they don’t, then no eggs would be “wasted”.

Aislinn Pearson
Aislinn Pearson (@aislinnpearson)
28 days ago

Dear Sokame, Thank you so much for posting here. It is always great to have updates on current research. I had a quick look at the list of natural enemies in FAW and noticed that these two species haven’t been recorded in the list, and this would also be a new record for Kenya. Would you kindly consider adding them to this list: https://faw.researchcollaborationportal.org/natural-enemies/ Alternatively I would also be happy to add them for you if that is more convenient for you, but it is always preferable that the researcher adds their own entries. It is after all your work,… Read more »