Dynamics of Clavigralla tomentosicollis in cowpea and trap influence on adult infestation
In southern Benin’s cowpea fields, the temporal dynamics and adult movement of Clavigralla tomentosicollis Stål were investigated during 1991 and 1992 by visual counting and mark-recapture methods. The pest’s phenology and adult movement were related to the pod and seed formation period. A rapid colonization by immigrating adults closely coincided with the pod formation phase of the plants. Oviposition occurred at the beginning of pod maturation and was succeeded by an increase of the nymphal density until pod harvest. The analysis of adult movement yielded daily emigration rates of 7 to 20% of the resident adult densities, while the daily percentage of in-situ adult mortality was below 5%. The decline in the number of adults towards harvest time is therefore mainly due to emigration rather than to field mortality. The high mobility of C. Tomentosicollis and the rapid field colonization suggest the use of trap crops as a control method. The use of pigeonpea as a trap border stripe in second season cowpea crops in 1991 and 1992 reduced the adult infestation level of C. tomentosicollis.