Mating behaviour, mate choice and female resistance in the bean flower thrips (Megalurothrips sjostedti)

Many species of thrips (Thysanoptera) in the family Thripidae form mating aggregations, but the adaptive significance of these aggregations and the extent of male and female mate choice is poorly understood. We studied the mating behaviour of the bean flower thrips Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), which forms male aggregations and occurs across sub-Saharan Africa. We tested whether males choose mates by female age or mating status. No-choice mating bioassays with one male and one female were used to simulate the way males usually encounter only one female at a time in aggregations in the field. Virgin females violently resisted mating attempts by males, but we found no compelling evidence to establish whether this was indiscriminate or was screening suitable males. Younger males (1–2 days old) did not discriminate females by age (1–2 or 7–10 days old), but older males (7–10 days old) avoided mating with older females. Any male choice by female mating status (virgin or mated) was weak or absent. The mating behaviour of M. sjostedti shows broad similarities with that of other thrips species that form aggregations, but also shows some distinct and novel differences, which can help our understanding of the adaptive significance of aggregations.

Exploiting Thrips Aggregation Pheromones to Develop a Lure-and-Kill Strategy for the Management of the Bean Flower Thrips

The potential of semiochemicals to lure insect pests to a trap where they can be killed with biopesticides has been demonstrated as an eco-friendly pest management alternative. In this study, we tested two recently characterized male-produced aggregation pheromones of the bean flower thrips Megalurothrips sjostedti (Trybom), namely (R)-lavandulyl 3-methylbutanoate (major) and (R)-lavandulol (minor), for their field efficacy. Moreover, compatibility of these pheromones and two other thrips attractants, Lurem-TR and neryl (S)-2-methylbutanoate, with the entomopathogenic fungus (EPF) Metarhizium anisopliae ICIPE 69 has been determined. Our study revealed that the M. sjostedti aggregation pheromones have dose-dependent antifungal effects on the EPF viability, but showed no fungistatic effect at a field-realistic dose for attraction of thrips. (R)-lavandulyl 3-methylbutanoate had similar antifungal effects as neryl (S)-2-methylbutanoate 8 days after exposure; whereas, Lurem-TR had a stronger antifungal effect than other thrips attractants. In the semi-field experiments, all autoinoculation devices maintained at least 86% viability of M. anisopliae conidia after 12 days of exposure. Field trials demonstrated for the first time that (R)-lavandulyl 3-methylbutanoate increases trap catches. Our findings pave a way for designing a lure-and-kill thrips management strategy to control bean flower thrips using autoinoculation devices or spot spray application.

Genetic variability and trait association under thrips (Megalurothrips sjostedti Trybom) infestation in cowpea (Vigna unguiculata [L.] Walp.)

Flower bud thrips is one of the most destructive insect pests of cowpea in sub-Saharan Africa. Information on genetic variability among cowpea germplasm and interrelationships among traits under thrips infestation would facilitate the development of resistant varieties. The objectives of the study were to assess genetic variability for thrips resistance, estimate heritability of yield and other traits and investigate inter-trait relationships under thrips infestation. One hundred and fifty-six cowpea lines, including one resistant and one susceptible check, were screened for resistance under natural infestation at two locations in Nigeria, in 2016. Test lines were scored for thrips damage weekly for three consecutive weeks, after removal of spreader plants, to obtain damage scores (DS) 1, 2 and 3 while data were collected on agronomic traits. The data were subjected to analysis of variance from which genetic components of the phenotypic variance were computed. Interrelationships among traits were determined using phenotypic and genotypic correlation, and sequential path analyses. Significant variability was observed among test lines. Lines TVu 6824 and TVNu 1307 were identified as possessing thrips resistance. DS3 had significant genetic and phenotypic correlations with DS1, DS2 and yield-related traits. Number of pods per peduncle, number of peduncles per plant and DS3 were identified as first-order traits. Heritability estimates ranged from 0.55 to 0.73. Genetic variability among the lines suggests the possibility of genetic control of thrips while number of pods per peduncle, number of peduncles per plant and DS3 would serve as useful selection criteria for thrips resistance.

Optimisation in vitro de l’efficacité des biopesticides dans la lutte contre les principaux ravageurs du niébé par la méthode des surfaces de réponse

La culture du niébé requiert de nos jours, une attention particulière à cause de sa sensibilité aux insectes ravageurs. La présente étude vise à déterminer, au laboratoire, les doses optimales de la combinaison des biopesticides (Topbio et virus MaviMNPV) à utiliser dans la lutte contre les principaux ravageurs du niébé notamment, Maruca vitrata, Aphis craccivora, et Megalurothrips sjostedti. A cet effet, les insectes ont été inoculés avec différentes doses des combinaisons de Topbio et du virus MaviMNPV variant respectivement de660 ml à 1000 ml et de 70 ml à 106 ml en utilisant la méthode des surfaces de réponses. La mortalité et la survie des insectes ont été évaluées et les doses optimales de la combinaison des biopesticides ont été déterminées. Les résultats ont montré que les effets linéaires et/ou quadratiques de la combinaison des biopesticides influencent significativement les taux de mortalité, d’émergence des larves et de mortalité des chrysalides. Ces taux ont varié de 63,33 à 85%, de 12,5 à 37,5%, et de 44,44 à 87,5% respectivement pour les taux de mortalité, d’émergence des larves et de mortalité des chrysalides de Maruca vitrata. Les taux de mortalité des formes adultes de Aphis craccivora, et Megalurothrips sjostedti, ont varié respectivement de 88,33 à 95% et de 85 à 95%. L’efficacité optimale des biopesticides est obtenue pour 1000 ml de Topbio et 106 ml du virus MaviMNPV avec un taux de désirabilité de 85%.Mots clés : Topbio, virus MaviMNPV, ravageurs, taux de mortalité, taux d’émergence

Pests and Diseases Associated with Yam Bean (Pachyrhizus erosus) Cultivation at Farmers’ Levels in the Central Region of Benin

Roots and tubers are one of the most important crops that provide food security in West Africa. Thus, Pachyrhisus erosus with its various potentials, is planned to be introduced in Benin to improve the nutritional quality of the population. Prior to that, this study aimed at assessing pests and disease of P. erosus in the agroecological conditions in the central parts of Benin. Conducted at experimental field in Savè during two consecutive years, experiments were laid in a completely randomized block design with 4 replications and three treatments including EC 533 and EC Kew cultivars of P. erosus and cowpea variety named Kpodji-Guèguè. Results showed that the major pests collected from P. erosus namely Ootheca mutabilis, Medythia quaterna, Piezotrachelus varium, Megalurothrips sjostedti and Brevipalpus phoenis were not so far reported in it. Compared to cowpea, pest’s infestation and their damages were lower on P. erosus. Infestation severity on leaves and the percentage of perforated green pods ranged from 0.7% to 3% against 0.8% to 88.9% and from 12.5% to 16% against 57.2% to 64% respectively on P. erosus and cowpea. Cercospora disease caused by Cercospora canescens and yam bean leaf blight caused by an unknown fungus were observed. Cercospora disease affected cowpea and P. erosus while yam bean leaf blight affected only P. erosus. This study provides additional data on pests and diseases associated with P. erosus worldwide and alerts farmers regarding their management.

Screening of 25 cowpea genotypes for resistance to Megalurothrips sjostedti Trybom in southern Ghana

In sub-Saharan Africa, Megalurothrips sjostedti Trybom are the most destructive insect pest of cowpea. It causes approximately 100% reduction in cowpea yield. Synthetic insecticides are widely used in controlling this pest, however, health and environmental hazards are another challenge. This study sought to evaluate 25 cowpea genotypes from Ghana, Mali, Nigeria, Niger, Burkina Faso, Togo and South-Sudan for resistance to this pest under field screening using a 5 by 5 alpha lattice design with 2 checks at University of Ghana farms. The results revealed Laduni 1B as resistant, 20 moderately resistant and 4 susceptible genotypes were also identified in this study. In the determination of correlated and non-correlated variables, ten traits were reported important to the resistance of cowpea genotypes to flower bud thrips. The genotypes with resistance could be used to introgress the resistant trait into other preferred but susceptible cowpea varieties.