Performance of cowpea weevil Callosobruchus maculatus (F.) infesting seeds of different Vigna unguiculata (L.) Walpers genotypes: The association between bruchid resistance and chitin binding proteins

Abstract

Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is an important pest of stored cowpea seeds (Vigna unguiculata) (L.) Walpers and the infestation of these seeds by the pest is a limitation to their production. Many studies have identified V. unguiculata genotypes that were resistant to the insect infestation. These resistant genotypes can lead to a reduction on the use of insecticides, avoiding environmental and food contamination. In this work, we evaluated the resistance or susceptibility of different V. unguiculata genotypes to infestation by C. maculatus. Our results showed that the number of eggs laid by C. maculatus varied from 6 to 13 eggs per seed among genotypes. Almost all the eggs were viable, and the larvae hatched at 5 days after oviposition (DAO). Larval survival was decreased in some genotypes, where only about 40% of the larvae survived. The mass of the larvae at 20 DAO ranged from 8.8 mg to 6.4 mg/larva. The emergence of adults was also decreased in some genotypes. The seed mass consumed by the larvae varied between 40 and 70% and affected seed germinability. Proteins similar to vicilins, glycinin, and CPRD22 were identified in V. unguiculata Pingo de Ouro 1-5-4 and MNC06-909-76 lines. Chitin-binding proteins were isolated from some genotypes and were toxic to the larvae at 1%. The docking of vicilin with chitin [(NAG)4] showed negative value of affinity energy, indicating a spontaneous binding. The vicilin interacted with (NAG)4 by hydrogen bonds, saline bridge, and hydrophobic interactions. These results suggest that part of the interference in the insect development, observed in some cowpea genotypes, may be due to the presence of chitin-binding vicilins.