An experiment to examine the effects of four agrometeorological factors on population fluctuations in legume pod borer, Monica testulalis (Geyer) in two cowpea varieties was carried out under field conditions in Ibadan, Nigeria. Plots, 5 x 10 m each, of cowpea varieties IT84S-2246–4 and Dan ilan were planted fortnightly between 5 May and 5 October 1988 (12 plantings in all for each variety). Three peaks of the pod borer populations were observed on the cowpeas. There were smaller peaks on crops planted between 5 May and 1 June and again between 29 June and 13 July and a larger one on those planted between 24 August and 7 September. These two peaks coincided with the peaks of the rainfall.
Significant relationships were obtained between pod borer counts and (a) cumulative rainfall (R2 = 0.41; P = 0.004) (b) number of rainy days (R2 = 0.17; P = 0.04) from plant emergence to 50% flowering. These results suggest though, the distribution of rainfall over time is more crucial than the total amount in determining the fluctuations of pod borer populations. Thus, the adjustment of planting dates is suggested as an IPM tactic to avoid the development of damaging levels of pod borer infestations.