The diamondback moth (DBM), Plutella xylostella L., is the most destructive pest affecting vegetable production in Kenya and around the world. Parasitoids have shown promising results in lowering the ...pest populations and damage caused by DBM. However, variations in host plant quality have been reported to have bottom-up effects up to the third and fourth trophic levels. We assessed the effects of two cultivated Brassica varieties (cabbage, Brassica oleracea var. capitata L. cultivar ‘Gloria F1′ and kale, B. oleracea var. acephala L. cultivar ‘Thousand headed’) on the development and performance of the specialist pest P. xylostella and two exotic parasitoids Diadegma semiclausum (Hellen) and Cotesia vestalis (Haliday). The exposed larval period of DBM took about 1.5 d longer on kale than cabbage and the total immature development time of both females and males was significantly longer on kale than cabbage. Higher pupal weight and higher fecundity were recorded on DBM fed on kale. Development time of D. semiclausum and C. vestalis was not affected by the host crop as was the parasitism rate of D. semiclausum. Heavier male pupae and larger adults of D. semiclausum, as well as more fecund adults of C. vestalis, were obtained from hosts fed on cabbage. Larger adults of C. vestalis were obtained from herbivores fed on kale. These results show potentially positive effects of host plant allelochemicals that are detrimental to herbivores while promoting parasitoid development and performance, which can be harnessed for the control of DBM.
The leaf-webber Spoladea recurvalis F. is the most devastating pest of amaranths in East Africa. Recent collaborative research in Asia and East Africa revealed one highly resistant amaranth accession ...(VI036227) to the pest and seven moderately resistant ones (RVI00053, VI033479, VI044437-A, VI047555-B, VI048076, VI049698, and VI056563). The solitary koinobiontic endoparasitoid Apanteles hemara Nixon has also been reported as efficient against the pest. Plant resistance to herbivores may have bottom-up effects on their parasitoids. In this study, we assessed the effects of the seven moderately resistant amaranth accessions and one susceptible accession (VI033482) on the performance of A. hemara. Except VI056563 that recorded lower parasitism rates compared to the susceptible accession, A. hemara performed well on all the other moderately resistant accessions.The longevity of the parasitoid was significantly extended on the resistant accessions compared to the susceptible one. While the parasitoid's body size, developmental time, and survival differed significantly between resistant accessions, they were similar to results obtained on the susceptible accession. Furthermore, while the parasitoid's sex ratio was male-biased in the susceptible accession, balanced sex ratios were obtained from accessions RVI00053, VI033479, VI044437-A, VI047555-B, VI048076, and VI049698. Significant nonreproductive host larval mortality was induced by A. hemara on all the tested accessions. These results suggest that the moderately resistant accessions can be used in combination with the endoparasitoid A. hemara to manage S. recurvalis and other amaranth leaf-webbers in the context of integrated pest management.
F. is a major pest moth of amaranth (
spp.) flowers worldwide, with a potential of causing complete foliage loss under severe outbreaks. Chemical insecticides are uneconomical for resource-poor ...farmers and pose health and environmental risks. Host plant resistance (HPR) to insects is an effective, economical and environmentally friendly alternative that is poorly understood and largely unexploited among traditional leafy vegetables. A total of 35 amaranth accessions were evaluated for the expression of their antixenotic and antibiotic traits against
, focusing on their effects on the biology of the pest in comparison with a susceptible accession. The accession VI036227 was found to be highly resistant against the pest, exhibiting exemplary antibiosis by causing 100% larval mortality within the first 36 h, despite not being deterrent for oviposition. The accessions VI048076, VI056563 and VI047555-B demonstrated moderate resistance against the pest for specific parameters including low oviposition, moderate early stage larval mortality and reduced adult longevity. Total mortality and weight gain in these three accessions were, however, not significantly different from the susceptible control. Higher numbers of eggs were laid in no-choice compared to choice situations. The implications of these findings in the management of
on amaranths are discussed.
The microgastrine parasitoid wasp Apanteles hemara Nixon, 1965, is currently being considered as a potential biocontrol agent of amaranth leaf-webber pests in Africa. To facilitate future research ...and identification of the species, we characterize it from an integrative taxonomy perspective by providing a comprehensive morphological redescription, extensive illustrations (including the first images of the holotype), DNA barcodes, wasp biology, host data (Choreutidae and Crambidae caterpillars), and updated geographical distribution of the species (including eight new country records). Despite a wide distribution across four major biogeographical regions (mostly within the Old World tropics), the species seems to be relatively uniform from a molecular and morphological perspective, based on studied specimens from Africa and Asia.
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