Host acceptability, suitability, interaction and establishment of two introduced Liriomyza leafminer endoparasitoids: Halticoptera arduine (Walker) (Hymenoptera: Pteromalidae) and Chrysocharis flacilla (Walker) (Hymenoptera: Eulophidae) in Kenya

Abstract

Liriomyza (Diptera: Agromyzidae) leafminers are pests of economic importance to the production of horticultural crops in East Africa. In the scope of a classical biological control program in East Africa, two parasitoids Halticoptera arduine (Walker) (Hymenoptera: Pteromalidae) and Chrysocharis flacilla Walker (Hymenoptera: Eulophidae) were introduced from Peru. This dissertation aims to assess the performance and impact of the parasitoids in biological control of Liriomyza leafminer species. Specifically, the research work aims to assess acceptability and suitability of the two parasitoids in three Liriomyza species, the potential interactions with a dominant local parasitoid, Diglyphus isaea (Walker) (Hymenoptera: Eulophidae), their establishment and spread after field release. In chapter two and three, performance data of the two exotic parasitoids in three Liriomyza leafminer flies are presented. Results show that the two parasitoids successfully accepted, parasitized, and completed their development in the three Liriomyza species in 15.97 ± 1.48 and 23.96 ± 0.88 d under controlled environments. Both parasitoids preferred to oviposit in L. huidobrensis (Blanchard) causing parasitism rates of between 27.96 ± 3.86 and 77.73 ± 4.39% across the hosts. Chrysocharis flacilla further induced significant non-reproductive pupal host mortality. Parasitoid F1 progenies were female-biased across the three hosts for C. flacilla except for a balanced sex ratio for H. arduine when reared on L. sativae Blanchard. Liriomyza huidobrensis yielded larger parasitoids and thus a good candidate for parasitoid mass rearing. In chapters four and five, the potential interactions between the two exotic parasitoids and the local parasitoid D. isaea were evaluated. Interaction results between H. arduine, C. flacilla, and D. isaea show perfect co-existence with no negative effect on performance of either of the parasitoids except on D. isaea’s when C. flacilla came after D. isaea. Halticoptera arduine and C. flacilla had superior parasitism rates over D. isaea. Host parasitism rate more than doubled (53.27 ± 4.99 and 72.96 ± 4.12%) when each of the exotic parasitoids occurred together with D. isaea as opposed to when D. isaea acted alone. Both D. isaea and C. flacilla caused significant non-reproductive host mortality. Presence of H. arduine and C. flacilla positively affected D. isaea reproduction as only female parasitoids cause host suppression. In chapter six, results of parasitoid establishments and spread in three agro ecological systems are presented. Liriomyza huidobrensis is the dominant species across the three agro ecological systems. Further, a complex of 14 parasitoid species is associated with Liriomyza leafminers. Halticoptera arduine and C. flacilla are confirmed to have established during the survey period of between January 2013 and June 2014. There is an increased in pest suppression of up to 40%, with C. flacilla causing substantive specific field parasitism of 3.5%. Seasons, cropping systems and host plants affected parasitoid establishment. Halticoptera arduine moved 10 km away from the release point. Chapter seven discusses the implications of the findings in the management of Liriomyza leafminers. This work shows promising candidates as biological control agents against Liriomyza leafminers. This research will hopefully influence the private and public sector in the East African region to adopt sustainable pest management strategies that will conserve the parasitoids which might lead to a reduction in the (over) reliance on synthetic pesticide by small holder producers of horticultural crops.