Better livelihoods from improved dual-purpose cowpea

Women farmers in a cowpea field. Photo by Sato Muranaka.
Women farmers in a cowpea field. Photo by Sato Muranaka.

Resource-poor cowpea farmers in northern Nigeria have seen their profits jump an average of 55 percent due to impro
Cheap Ralph Lauren Companies  ved dual-purpose cowpea varieties that we and our partners developed and introduced.

Farmers who use traditional varieties earn about US$251 per hectare, while those who are growing the improved cowpea are getting matters, which is shopbust because   US$390, or US$139 more, per hectare with proper crop management.

The improved varieties: IT89KD-288, IT89KD-391, IT97K-499-35, and IT93K-452-1 produce high-quality grains that are used by farmers for food and fodder. They are also resistant to Striga, a parasitic weed that reduces yields of susceptible local cowpeas by as much as 80 percent.

Over 100,000 farmers in Borno and Kano states in northern Nigeria and in the Niger Republic are currently using the improved varieties, where their adoption rate is conservatively estimated at 65 percent.

Farmers in the savannah region view cowpea as both food and cash crop. When the varieties were introduced, farmers took to them readily since they serve both ends well. Those who cultivate the dual-purpose cowpeas are basically better off than those who do not.

The improved cowpea varieties were developed and deployed in partnership with the Borno State Agricultural Development Project, Kano State Agricultural and Rural Development Authority, Kaduna State Agricultural Development Project, the Institute of Agricultural Research – Zaria and the University of Maiduguri.

Other local development partners are promoting the improved varieties by organizing farmers’ field days, exchange visits, training and farmer-to-farmer diffusion.

Cowpea is a grain legume grown mainly in the savanna regions of the tropics and subtropics in Africa, Asia, and South America. Its grain contains about 25 percent protein, making it extremely valuable to those who cannot afford more expensive animal-derived protein sources such as meat and fish. It is tolerant to drought, fixes atmospheric nitrogen, and improves poor soils.

The FAO, about 7.56 million tons of cowpeas are produced worldwide annually, with sub-Saharan Africa accounting for 70%, or about 5.3 million tons, of global production.

Advances in the biological control of the cowpea pod borer

Apanteles taragamae
Apanteles taragamae. Photo by Georg Goergen, IITA.

Ecological studies carried out at the World Vegetable Center (AVRDC) in Taiwan identified the parasitoid Apanteles taragamae as the most promising for controlling the legume pod borer Maruca vitrata in Africa. To test its effectiveness, our researchers in Benin imported A. taragamae under standard quarantine protocols and carried out experimental releases in Benin, Ghana, and Nigeria in 2007 on patches of wild vegetation including plants known to host the pod borer such as Lonchocarpus sericeus, Pterocarpus santalinoides, Lonchocarpus cyanescens, and Tephrosia spp.

Prior to these releases, we had studied the host searching capacity of A. taragamae using a 4 arm-olfactometer, and flowers of three different host plants: cowpea, Pueraria phaseoloides and the three Lonchocarpus sericeus. These studies revealed that A. taragamae uses kairomone-mediated host recognition at the short to medium range.

From as early as six months after the first releases and up until 2009, we conducted a series of surveys to monitor establishment of the parasitoid. Although we were not able to successfully recover the released parasitoid, we got indirect evidence of its establishment in the environment. We ruled out that interspecific competition with indigenous parasitoids exploiting M. vitrata larvae of the same age and on the same host plant could be the cause for this lack of evidence because we had conducted, just before the releases, elaborate competition studies which did not reveal any problems. Also, in its area of origin in Taiwan, A. taragamae coexists with similar parasitoid species found in Benin e.g. Phanerotoma sp. and Dolichogenidaea sp.

A Maruca vitrata larva. Photo by IITA.
A Maruca vitrata larva. Photo by IITA.

In Taiwan, however, A. taragamae is found prevalently on the cover crop Sesbania cannabina, which is difficult to grow in West Africa because of foliage beetles, particularly Mesoplatys sp. that completely defoliates the plant. We recently intensified our studies on African indigenous species of Sesbania that suffer less beetle damage, but so far there have been no signs of direct establishment. This is despite screenhouse experiments confirming the suitability of Sesbania species as feeding substrate for the pod borers and also as host for foraging parasitoids.

From 2007 onwards, we also started testing the newly-discovered Maruca vitrata Multi-Nucleopolyhedrosis Virus (MaviMNPV) found in Taiwan through collaborative studies with AVRDC. After a series of laboratory tests which confirmed the Taiwan results, we carried out host range studies to ascertain its specificity. Of the seven lepidopteran species tested (four Pyralids, two Noctuids, and one Crambid), none got infected by MaviMNPV applied on artificial diet. We then tested the virus in semi-natural condition using field cages with artificial infestations of M. vitrata larvae. Results showed a very high mortality of pod borer larvae (>95%) using standard concentrations comparable to those found in commercial formulation of entomopathogenic viruses (e.g. against the cotton bollworm Helicoverpa armigera).

Characteristic symptom of Maruca vitrata attack on cowpea. Photo by IITA.
Characteristic symptom of pod borer attack on cowpea. Photo by IITA.

In the Mono region of Benin, we discovered a few pod borer larvae with apparent signs of MaviMNPV close to the release sites of the parasitoids. This observation was important since we did not carry out open field experiments nor has MaviMNPV been found in West Africa prior to its introduction in 2007. We hypothesized that the parasitoid A. taragamae could have transmitted MaviMNPV to pod borer larvae.

To verify this, we deliberately infected pod borer larvae using three methods: ovipositor only, whole body without ovipositor, and through artificial diet. The parasitoid was able to transmit the virus to the larvae through all of the infection methods.

This finding was significant as the parasitoid could spread the virus without further intervention. This is also indirect evidence that A. taragamae is present in the environment, albeit in low levels, which cannot be detected by current sampling methods, or on yet unknown secondary host plants for M. vitrata. We are currently conducting collaborative studies in our virology lab in Ibadan to identify and ascertain the mechanisms of transmission, and duration of virus retention and transfer.