Modeling Evolution of Resistance by Maruca vitrata (Lepidoptera: Crambidae) to Transgenic Insecticidal Cowpea in Africa

We created a detailed model of the Maruca vitrata (F.) and cowpea [Vigna unguiculata (L.) Walp] system to study the possible evolution of resistance by the insect to transgenic insecticidal cowpea, which is under development. We focused on population dynamics and genetics in a region of west Africa. We simulated single-toxin and pyramided (two-toxin) cowpea and emphasized conservative, worst-case scenarios in our analysis. The results indicate that as long as a pyramided, transgenic cowpea can be developed, seed saving by farmers and reliance on natural refuge are not major problems for resistance management. Furthermore, it is possible that one or both toxins in the pyramid may not need to be high dose for evolution to be delayed significantly (>20 yr or 80 generations for resistance to become a concern if transgenic cowpea is deployed in areas where M. vitrata is endemic). If efforts are made to deploy transgenic cowpea only into the regions where M. vitrata is not endemic, then there is little to no concern with resistance emerging in the M. vitrata populatio

An assessment of the risk of Bt-cowpea to non-target organisms in West Africa

Cowpea (Vigna unguiculata Walp.) is the most economically important legume crop in arid regions of sub-Saharan Africa. Cowpea is grown primarily by subsistence farmers who consume the leaves, pods and grain on farm or sell grain in local markets. Processed cowpea foods such as akara (a deep-fat fried fritter) are popular in the rapidly expanding urban areas. Demand far exceeds production due, in part, to a variety of insect pests including, in particular, the lepidopteran legume pod borer (LPB) Maruca vitrata. Genetically engineered Bt-cowpea, based on cry1Ab (Event 709) and cry2Ab transgenes, is being developed for use in sub-Saharan Africa to address losses from the LBP. Before environmental release of transgenic cowpeas, the Bt Cry proteins they express need to be assessed for potential effects on non-target organisms, particularly arthropods. Presented here is an assessment of the potential effects of those Cry proteins expressed in cowpea for control of LPB. Based on the history of safe use of Bt proteins, as well as the fauna associated with cultivated and wild cowpea in sub-Saharan Africa results indicate negligible effects on non-target organisms

Annual cycle of the legume pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) in southwestern Burkina Faso

Maruca vitrata is an economically significant insect pest of cowpea in sub-Saharan Africa. Understanding the seasonal population patterns of M. vitrata is essential for the establishment of effective pest management strategies. M. vitrata larval populations on cultivated cowpea and adult flying activities were monitored in addition to scouting for host plants and parasitoids during 2 consecutive years in 2010 and 2011 in southwestern Burkina Faso. Our data suggest that M. vitrata populations overlapped on cultivated cowpea and alternate host plants during the rainy season. During the cowpea off-season, M. vitrata maintained a permanent population on the wild host plants Mucuna poggei and Daniella oliveri. The parasitoid fauna include three species, Phanerotoma leucobasis Kri., Braunsia kriegeri End. and Bracon sp. Implications of these finding for pest management strategies are discussed

Integrated management of cowpea insect pests using elite cultivars, date of planting and minimum insecticide application

Trials were conducted in Kano, northern Nigeria, during 1996 and 1997 cropping seasons to determine the influence of date of planting and two well-timed insecticides sprays on the incidence of major insect pests namely, the legume pod-borer, Maruca vitrata Fab., legume flower thrips, Megalurothrips sjostedti Trybom, complex of pod-sucking bugs and cowpea aphid, Aphis craccivora Koch and their effect on grain yield of elite cowpea (Vigna unguiculata L. Walp) cultivars from International Institute of Tropical Agriculture (IITA) breeding programme. Six cultivars were planted at 4 different dates between 13 June and 12 August 1996 whilst 12 cultivars were planted at 5 different dates between 5 June and 12 August 1997 with and without insecticide protection. Aphid infestation occurred only on cowpea planted between the first week of June and mid-July with the highest incidence recorded on crop planted in the last week of June. Cowpea planted in June flowered and podded between early to mid-August when post-flowering pests (M. vitrata, M. sjostedti and Clarigralla tomentosicollis) densities were relatively low and produced significantly higher grain yields without insecticide protection compared to other planting dates. The flowering and pod formation stages of late planted (July and August) crops coincided with the peak population densities of the three major post-flowering pests resulting in a considerable reduction of grain yield. Overall, IT90K-277-2, IT93K-734, IT93K-452-1 and IT93K-513-2 performed best whereas IT86D-719, IAR-48 and Dan Ila gave the poorest performance when unsprayed. Two insecticide sprays of Cypermethrin + dimethoate (Sherpa plus ®) (30 + 250g a.i. ha-1) at but initiation and 50% flowering stages increased grain yields considerably from 225 to 900 kg ha-1 for cowpea planted in July and August. Cost-benefit analysis indicated that the insecticide application was more profitable for cowpea planted in late July and August than was the case when planted in June and early July. This seems to suggest that early maturing elite cultivars could escape economic damage caused by post-flowering pests when cowpea is planted early in the season. The implication of these findings to the grower and the breeding strategy at IITA is discussed in this paper. RÉSUMÉ Des essais ont été conduits durant les saisons culturales de 1996 et 1997 à Kano au nord du Nigeria pour déterminer l'influence de la date de plantation et la pulverization de deux insecticides bien connus sur l'incidence des principaux insectes à savoir les boreurs des gousses des légumineuses, Muruca vitrata Fab., les thrips des fleurs des légumineuses, Megalurothrips sjostedti Trybom, le complexe des punaises pipeuses des gousses et les aphides du niébe, Aphis craccivora Koch et les effets sur le rendement grain des cultivars élites du niébe du programme d'amélioration de l'IITA. Six cultivars ont été plantés à quatre differentes dates entre le 13 Juin et le 12 Août 1996 alors que 12 cultivars ont été plantés à cinq differentes dates entre le 5 Juin et le 12 Août 1997 avec ou sans protection d'insecticide. L'infestation des aphides ont apparu seulement sur le niébe plantés entre la première semaine de juin et mi-juillet avec l'incidence la plus élevée observée sur les cultures plantées dans la dernière semaine de Juin. Le niébe planté en Juin a fleuri et formé des gousses entre très tôt et mi-Août quant les densités des pestes post floraison (M. vitrata, M. sjostedt et C. tomentosicollis) étaient relativement faibles et ont produit significativement des rendements grains très élevés sans insecticides comparés aux autres dates de plantation. Les stades de floraison et de formation des gousses des cultures plantées plus tard (Juillet et Août) ont coincidé avec les densités plus élevées de trois majeurs pestes pot-floraison résultant à une réduction considérable du rendement grain. En général, IT90K-277-2, IT93K-734, IT93K-452-1 et IT93K-518-2 ont été les meilleurs alors que IT86D-719, IAT-48 et Dan Iia ont eu une pauvre performance lorsqu'ils étaient no pulverisés. Les pulverizations de l'insecticide de Cypermethrin + dimethoate (Sheroa plus R ) (30 + 250g a.i ha-1) à l'initiation et 50% des stades de floraison ont augmenté les rendements grains considérablement de 225 à 900 kg ha-1 pour le niébe planté en Juillet et Août. L'analyse du coût-bénéfice a indiqué que l'application de l'insecticide était plus profitable pour le niébe planté tard en Juillet et Août plus que le cas du niébe planté en Juin et début Juillet. Ceci semble indique que les cultivars élites plus précoces pourraient échapper aux domages économiques causés par les pestes post floraison quant ils apparaissent avant dans la saison. Les implications de ces résultats pour les cultivateurs et la stratégie d'amélioration pour l'IITA sont dicutées. (Af Crop Science and Production: 2001 9(4): 655-666