Field release and recovery of leafminer endoparasitoid Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae), its interactions with local parasitoids and behavioral responses to hosts in vegetable production systems in Kenya

Abstract

Liriomyza leafminers (LMF) (Diptera: Agromyzidae) are severe pests of vegetables and ornamentals worldwide. Parasitoids complex regulate LMF populations in their native and invaded areas while in Kenya, previous studies reveal low LMF parasitism (<6%) across all agro ecological zones. The endoparasitoid Phaedrotoma scabriventris Nixon (Hymenoptera: Braconidae) was therefore imported from Peru to improve on LMF management at different agroecological zones of vegetable production in Kenya. This study evaluated the potential of P. scabriventris for biological control of LMF, its interactions with local parasitoids and behavioural responses to hosts in vegetable production systems in Kenya. Using single, sequential and simultaneous release laboratory assays of P. scabriventis and O. dissitus on L. huidobrensis-infested Vicia faba plants, individual parasitism rates of both parasitoid species were not affected. However, the sequence release resulted in the second released species achieving a significantly lower parasitism rate than when released alone, simultaneously or as first released species. The F1 progeny sex ratios of both parasitoid species were not significantly affected whether in single, simultaneous or sequential releases and was female biased for P. scabriventris and male biased for O. dissitus. Montly field surveys of infested incubated LMF host plants from November 2011 - November 2012 revealed three Liriomyza species (L. huidobrensis (Blanchard), L. sativae Blanchard and L. trifolii (Burgess)), represented 99.8% of total LMF recorded. Of these, L. huidobrensis was the greatest challenge to vegetable production, being the most abundant and most polyphagous species at all elevations and seasons. Liriomyza species were collected from all infested incubated leaves of 20 crops surveyed with Fabaceae and Solanaceae crops being the most infested hosts. Nine parasitoid species were recorded with 31% total parasitism. Diglyphus isaea (Walker) (Hymenoptera: Eulophidae), P. scabriventris and O. dissitus, were the most abundant at all elevations. Phaedrotoma scabriventris was recovered from all released sites. Surveys from November – December 2013 revealed spread P. scabriventris away from the release sites to 40 km, 30 km and 50 km at high, mid and low elevations, respectively. Diglyphus isaea was more abundant at the high- and midlands at all seasons compared to the lowlands while the lowland favoured abundance of P. scabriventris and O. dissitus during the long rain compared to high- and midlands at other seasons. These parasitoids performed better on kidney bean and French bean at all elevations. Using dual choice olfactometer assays, P. scabriventris was significantly attracted to odours from L. huidobrensis damaged host plants; Phaseolus vulgaris L., Pisum sativum L. and V. faba L. and avoided mechanically damaged ones when compared against clean air controls. However, P. scabriventris preferred neither the clean air controls nor any of the healthy plants. These findings suggest that P. scabriventris has no detrimental effect on O. dissitus and its release into Kenya’s agricultural ecosystems will enhance LMF management. The finding that L. huidobrensis dominates at all elevations challenges the long held consideration of L. trifolii as the dominant LMF in Kenya. Recovery of P. scabriventris from all release sites and its spread to different Liriomyza-infested crops two year post release, suggest its successful establishment and potential for wide spread. Behavioural responses of P. scabriventris to the three L. huidobrensis host plant species provide evidence for differences in the parasitoid’s response pattern to L. huidobrensis host plants and the volatile profiles induced by the different treated plant species. These results are discussed in relation to biological control and wider ecological implications. For improved LMF management, it is important to determine if there are genetic differences between L. huidobrensis identified in Kenya and that in countries where the species is still limited to higher elevations. Continuous field evaluation of the effectiveness of P. scabriventris performance and spatial distribution in Kenya agro-ecological zones over the years are necessary. Expansions of chemical, electrophysiological and behavioral studies are also needed to unravel the chemical basis of host finding and location in P. scabriventris.