The relative susceptibilities of 43 cowpea varieties to damage by Cydia ptychora (Meyrick) under chemical protection with monocrotophos, were investigated in field trials at Ile-Ife, Nigeria. The results revealed significant varietal differences, with the moderately resistant varieties ER-7, BPL-3-1 and EW/1 consistently showing relatively low damage. These varieties may be useful in planning an integrated pest management programme involving minimum insecticide treatment.

Cohort tests in screened cages confirmed that the cowpea varieties TVu 2994, TVu 3709, EW/1, BPL-3–1, ER-7 and Vita 5 have promising levels of resistance to Cydia ptychora (Meyrick). The resistance was found to be mainly explained by antixenosis with respect to oviposition.

In no-choice tests in the laboratory, high larval mortality was recorded in TVu 3709 and BPL-3–1. Additionally, comparatively lighter-weight final instar larvae and adult females with reduced fecundity, fertility and longevity were reared from TVu 3709 and TVu 2994. Larvae reared on Vita 5 were slower in developing to adults than on other varieties; they were also relatively lighter in weight, while adults emerging from them showed reduction in size and fecundity. It is therefore concluded that resistance in TVu 3709, TVu 2994, BPL-3–1 and Vita 5 is partly due to larval antibiosis.

Assessment of the damage potential of Cydia ptychora (Meyrick) was carried out in Ife Brown cowpea at different levels of larval infestation and different pod growth phases. The results showed that C. ptychora caused significant shrivelling in pods of Ife Brown cowpea when infested with either one, two or three first-instar larvae per pod at either the young or mid-fill growth phases, relative to the corresponding controls. A significant reduction in seed yield was also recorded in plants subjected to an infestation level of either one, two or three first-instar larvae per pod at both mid-fill and mature pod growth phases. Thus, an infestation level of one first-instar larva per pod at either the mid-fill or mature pod growth phases would be adequate for intensive screening of cowpea varieties for resistance to C. ptychora, using Ife Brown as a standard for comparison.

The trends in flowering, podding and seed yield of four cowpea varieties planted at different times of the growing season in 1975 and 1976, were studied along with the associated pest activity. Flowering, podding and seed yield were found to decrease over the season from April to September irrespective of whether the crop was protected against insect pests or not. However, there seemed to be two peak periods of pest activity—April to July and October to December—when severe damage to the crop occurred in unprotected plots. Planting in June or July usually led to an escape from several major pests even though the cool night temperatures and incidence of overcasts at that period seem to preclude optimal reproductive performance of the crop.

The pattern of insect pest succession on the crop over the season is discussed and it is suggested that for small farm holders in Southern Nigeria, who are unlikely to apply insecticides, planting in June is advisable.