The legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae), an important insect pest of cowpea: a review emphasizing West Africa

The legume pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) is a pantropical insect pest of legumes. In West Africa M. vitrata is the most devastating insect pest of cowpea, a food crop providing much-needed, inexpensive protein to farmers and consumers. Various approaches to controlling this pest have been tried, including cultural management, host plant resistance and use of synthetic and botanical pesticides, all with limited success. In this review we present information on the distribution, morphology, molecular characteristics, behavior and host plants of M. vitrata. We give especial attention to innovative management tactics being developed for West Africa, including genetically engineered Bt cowpea, new biopesticides and use of exotic parasitoids. We discuss research needs for enhancing integrated pest management (IPM) for M. vitrata in Africa

Distribution and diversity of alternate hosts of Maruca vitrata Fabricius in three West African countries

The evolution of resistance to the Bacillus thuringiensis (Bt) toxins by insect pests is a major threat to Bt technology. However, the rate of resistance can be slowed with appropriate integrated insect resistance management (IRM) strategies. Surveys were conducted to identify alternate host species for Maruca vitrata (commonly called the legume pod borer or Maruca) that could serve as refuges for Pod-Borer Resistant (PBR) cowpea in three West African countries (Ghana, Nigeria, and Burkina Faso). Survey sites included 25 in northern Ghana, 44 in northern Nigeria, and 52 in north-central and southwestern Burkina Faso. Alternate hosts of Maruca identified from plant species belonging to the Fabaceae family that showed signs of Maruca damage on cowpea tissues were collected and dissected. Larvae that were found during these dissections were reared to adult moths in the laboratory then identified to species. The alternate host plants including species of Crotolaria, Sesbania, Tephrosia, and Vigna were the most frequently encountered among sites and locations. Flowering and podding of these plants overlapped with flowering and podding of the nearby (~200 m) cowpea crop. Abundance of these wild hosts and overlapping flowering patterns with the cowpea crop in most locations have the potential to sustain ample numbers of Bt susceptible Maruca that will mate with possible resistant Maruca and deter resistance development. Further quantitative studies, however, are required from each location to determine if actual Maruca production from alternate hosts is sufficient for a PBR IRM strategy. If verified, this approach would be compatible with the high dose/refuge IRM strategy that includes alternate hosts and non-Bt crops as refuges

Efficacy of a cry1Ab Gene for Control of Maruca vitrata (Lepidoptera: Crambidae) in Cowpea (Fabales: Fabaceae)

Cowpea [Vigna unguiculata (L) Walp.] is an important staple legume in the diet of many households in sub-Saharan Africa. Its production, however, is negatively impacted by many insect pests including bean pod borer, Maruca vitrata F., which can cause 20–80% yield loss. Several genetically engineered cowpea events that contain a cry1Ab gene from Bacillus thuringiensis (Bt) for resistance against M. vitrata were evaluated in Nigeria, Burkina Faso, and Ghana (West Africa), where cowpea is commonly grown. As part of the regulatory safety package, these efficacy data were developed and evaluated by in-country scientists. The Bt-cowpea lines were planted in confined field trials under Insect-proof netting and artificially infested with up to 500 M. vitrata larvae per plant during bud formation and flowering periods. Bt-cowpea lines provided nearly complete pod and seed protection and in most cases resulted in significantly increased seed yield over non-Bt control lines. An integrated pest management strategy that includes use of Bt-cowpea augmented with minimal insecticide treatment for protection against other insects is recommended to control pod borer to enhance cowpea production. The insect resistance management plan is based on the high-dose refuge strategy where non-Btcowpea and natural refuges are expected to provide M. vitrata susceptible to Cry1Ab protein. In addition, there will be a limited release of this product until a two-toxin cowpea pyramid is released. Other than South African genetically engineered crops, Bt-cowpea is the first genetically engineered food crop developed by the public sector and approved for release in sub-Saharan Africa

IPM-omics: from genomics to extension for integrated pest management of cowpea

Insect pests often develop resistance to insecticides, and such resistance represents a serious management problem. Devising methods that concurrently delay resistance and minimize injury by insects to field crops and stored grain has long been a goal of Integrated Pest Management (IPM). A centerpiece of IPM has been the combined use of biological control agents and prudent application of chemical insecticides. Unfortunately, successful application of IPM has remained a challenge. This chapter describes the use of emerging genomic technologies that may lead to a “systems” perspective of IPM for the control of pests of cowpea and other crops. This emerging field, which we refer to as “IPM-omics”, builds upon recent advances in genome sequencing technologies and detection of largescale gene polymorphisms, which are becoming economically feasible for pest insect systems. IPM-omics will also need to involve the use of information and communications technologies both to collect critical information on pest populations and to deploy practical IPM solutions. The information obtained on the temporal fluctuations, spatial distribution, and ecological diversification within target, non-target, and natural enemy populations can be overlaid on a geographic information systems (GIS) map to predict pest outbreaks and to decide how to apply control measures. The “systems” perspective of organism communities provided through IPM-omics may also facilitate the effective evaluation, modification, and optimization of IPM strategies. However, any resultant IPM program for crop pests will also require that extension agents, government agencies, and non-governmental organizations (NGOs) have the ability to easily access and deploy the IPM research findings through information and communications technologies. Thus, we also outline the need for an online system that facilitates the sharing and peer review of practical IPM outputs. Many of these tools are currently being developed to help farmers manage insect pests of cowpea in West Africa

IPM-omics: from genomics to extension for integrated pest management of cowpea

Insect pests often develop resistance to insecticides, and such resistance represents a serious management problem. Devising methods that concurrently delay resistance and minimize injury by insects to field crops and stored grain has long been a goal of Integrated Pest Management (IPM). A centerpiece of IPM has been the combined use of biological control agents and prudent application of chemical insecticides. Unfortunately, successful application of IPM has remained a challenge. This chapter describes the use of emerging genomic technologies that may lead to a “systems” perspective of IPM for the control of pests of cowpea and other crops. This emerging field, which we refer to as “IPM-omics”, builds upon recent advances in genome sequencing technologies and detection of largescale gene polymorphisms, which are becoming economically feasible for pest insect systems. IPM-omics will also need to involve the use of information and communications technologies both to collect critical information on pest populations and to deploy practical IPM solutions. The information obtained on the temporal fluctuations, spatial distribution, and ecological diversification within target, non-target, and natural enemy populations can be overlaid on a geographic information systems (GIS) map to predict pest outbreaks and to decide how to apply control measures. The “systems” perspective of organism communities provided through IPM-omics may also facilitate the effective evaluation, modification, and optimization of IPM strategies. However, any resultant IPM program for crop pests will also require that extension agents, government agencies, and non-governmental organizations (NGOs) have the ability to easily access and deploy the IPM research findings through information and communications technologies. Thus, we also outline the need for an online system that facilitates the sharing and peer review of practical IPM outputs. Many of these tools are currently being developed to help farmers manage insect pests of cowpea in West Africa