Evaluation of resistance in different cowpea cultivars to Callosobruchus maculatus infestation

Abstract

Cowpea [Vigna unguiculata (L.) Walp] seeds are an important source of nutrients for human and animal. However, part of the seed production is lost due to insect attacks, mainly by the weevil Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae), a major pest of stored cowpeas. An efficient method for controlling seed infestation is the use of insect-resistant cultivars. In this work, we studied the resistance of different cowpea Brazilian cultivars (BRS) to infestation and damage by C. maculatus. Our results showed that some cultivars interfered in female oviposition. The time necessary for the larvae to perforate the seed coat of some cultivars increased up to 40 %. No relationship between seed coat thickness, textures, or pigmentation and the larval ability of crossing seed coats was observed. Larval survival was also affected by cowpea cultivars. In BRS Xiquexique, only 30 % of the larvae survived at 20 days after oviposition. The weight of larvae developed into BRS Pajeu, and BRS Xiquexique cultivars decreased about 50 %. Cysteine protease, α-glucosidase, and α-amylase activities decreased in larvae developed in some cultivars, mainly in Pajeu, Guariba, Tucumaque, and Xiquexique. Adult emergence also decreased in Xiquexique, Pajeu, Tucumaque, and Paraguacu BRS cultivars. A direct relationship between higher infestation and lower seed germination and seedling growth potential was observed. From these data, we would recommend the use of Pajeu, Guariba, Tucumaque, and Xiquexique BRS cultivars as a way to reduce cowpea infestation, and suggest that their resistance mechanism is related to the diminishment of larval digestive abilities.