Effect of two agro-ecological zones on insect species of cowpea (Vigna unguiculata L.) Walp during the late cropping season, Delta State, Southern Nigeria

Abstract

The study was conducted in two agro-ecological zones to identify and compare insect species associated with cowpea (Vigna unguiculata (L.) Walp Delta State during the late cropping season of 2005. Asaba in Oshimili South Local Government Area of Delta State lies in the northern drier part of Delta State, south Nigeria while Abraka in the same state is located in the south and experiences a more humid weather. Both locations are about 135 kilometres apart. The results showed that the occurrence and distribution of insect species followed different trends. There were 10 insect orders, 24 families and 39 species in Asaba while Abraka recorded 8 insect orders, 23 families and 35 insect species. The heteroptera with relative abundance of 28.2% were the dominant species at Asaba, while coleoptera (28.6%) were the most dominant species at Abraka in the late season. Orthoptera (8.6%) were slightly more at Abraka than Asaba with 5.1% relative abundance. Nine insect species recorded at Asaba were absent at Abraka. Conversely, four insect species on the crop at Abraka were absent in Abraka. Ootheca mutabilis Sahl, Aphis craccivora Koch, Megalurothrips sjostedti Trybom, Maruca vitrata Fab and coreid bugs such as Clavigralla tomentosicollis Stal, Anoplocnemis curvipes Fab, C. shadabi Doll, Aspavia armigara Fab, Nezara virudula, Mirperus jaculus were the key insect pests in the study areas. More insect species occurred in Asaba compared to Abraka.