Stored Cowpea Seeds Research Articles

Evaluation of powdered fruits of four peppers (Capsicumspp.) for the control ofCallosobruchus maculatus(F) on stored cowpea seed

Abstract The efficacy of two application rates of powdered fruits of four types of peppers (Capsicum spp.) was evaluated for the control of Callosobruchus maculatus (F). The various pepper powders at 2.5 g‐5.0 g per 250 g of seed were effective in reducing oviposition and damage to cowpea seeds. The pepper type Capsicum frutescens var. yarmunchi was the most effective in discouraging oviposition and minimizing damage to the seed, as indicated by the significantly lower number of emergence holes. The seed quality and viability were not affected by the powdered pepper fruit treatment. The result is indicative of the potential for the use of powdered fruits of some peppertypes in protecting stored cowpea seeds against C. maculatus.

Responses of three populations of the seed beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), to seed resistance in selected varieties of cowpea, Vigna unguiculata (L.) Walp.

The seed beetle, Callosobruchus maculatus (F.), is the major pest of stored cowpea seeds. It is currently known to exist as geographically distinct populations (biotypes) which vary in many biological parameters. Numerous varieties of cowpea which exhibit significant levels of resistance to a single Nigerian strain of the beetle have been bred at the International Institute of Tropical Agriculture. In this study, 11 purportedly resistant varieties as well as two susceptible ones were evaluated against three populations of the beetle originating from Cameroon, Brazil and Burkina Faso, adopting a stringent experimental protocol. For each biotype, the resistant cowpeas were distinguished from the susceptible ones in terms of larval survival, developmental period, adult weight at emergence and lifetime female fecundity. These different variables were significantly correlated with each other. Larval survival was poorer on the resistant cowpeas but estimation of this and other parameters is subject to variation due to differences in the period of observation of infested seeds. Food consumption by each larva was generally similar in susceptible as well as the resistant cowpeas. Slower development of surviving larvae produced smaller adults which were less fecund in some resistant cowpeas but not in others. The Campinas population appears to be more adversely affected by the resistant cowpeas than the populations from Cameroon or Burkina Faso. It is demonstrated that the design of assays for resistance needs great care and can affect conclusions. The responses of populations (biotypes) of C. maculatus to cowpea varieties show such variability that studies using single populations are of limited or no practical value.

Oviposition deterrence and ovicidal properties of some plant powders against Callosobruchus maculatus in stored cowpea (Vigna unguiculata) seeds

SUMMARYPowders made from 15 plant species were tested in the laboratory against C. maculatus on stored cowpea seeds. Fewest eggs were laid on seeds mixed with Nicotiana tabacum powder. Few eggs were also laid on seeds mixed with powders obtained from Erythrophleum suaveolens and Ocimum gratissimum. N. tabacum powder, followed by E. suaveolens powder, was the most effective in reducing egg hatch.

Observations on the bionomics of Laspeyresia ptychora Meyr. (Lepidoptera, Eucosmidae) infesting cowpea in Nigeria

One of the principal pests of cowpea (Vigna unguiculata) in southern Nigeria is Laspeyresia ptychora Meyr., the larvae of which attack the seeds within mature pods and cause considerable loss of yield. It has not so far been recorded from northern Nigeria. Details of the life-history of this Eucosmid are described from laboratory and field observations made in Nigeria in 1962–63. Eggs are laid on mature pods, which the larvae enter very soon after hatching, feeding on the seeds within. Pupation normally takes place in a cocoon in the soil, but pupal development can be completed in the absence of soil and of a cocoon. Four generations normally occur on the two crops of cowpea that can be grown each year in southern Nigeria, a complete first and a partial or complete second generation on each; but five generations may sometimes occur. The pest survives through the dry season and between the two crops in the rainy season by means of generations that develop on stand-over and volunteer cowpea, on leguminous plants grown in market gardens, and possibly on some yet undiscovered wild plant. No diapause in any stage was observed.Annual fluctuations in larval populations and levels of infestation are described in relation to the cowpea crops and to the damage caused. In a field trial in 1963, 35 per cent, (by weight) of seed from the early crop and 20 per cent, of that from the late crop was damaged. These figures take no account of seed that was completely destroyed, so that the true losses are greater than they indicate. Damaged seed is usually unmarketable as a result of contamination with frass and webbing.Investigations showed that, although larvae may be carried into stores when the crop is harvested, L. ptychora cannot become a pest of stored cowpea seeds because it is unable to develop on dried seeds.The possibilities of chemical, cultural and biological control are discussed, the latter not at present being promising. Field trials with γ BHC, dieldrin, carbaryl, isobenzan and phosphamidon were carried out; only the last-named, which is a systemic insecticide, showed promise of affording satisfactory control. The difficulties of successfully attacking L. ptychora with insecticides are discussed, and it is concluded that chemical measures will need the support of modified cultural practices, particularly those directed towards destruction of stand-over and volunteer cowpea plants, if a satisfactory level of control is to be achieved.