Influence of secondary host plants on the embryonic and larval development of Callosobruchus maculatus (Coleoptera: Chrysomelidae, Bruchinae)

Insects in general and beetles in particular, are endowed with a behavioral plasticity which allows them to adapt readily to plants, whether they belong to the same family or not[1;2;3]. The diet of insects of the subfamily Bruchinae, to which Callosobruchus maculatus (Coleoptera: Chrysomelidae, Bruchinae) belongs, is characterized by a high degree of host specialization; their larvae are found inside the seeds of a small number of host plants species[4;5]. Callosobruchus maculatus is a cosmopolitan pest species of cowpea in the tropics and subtropics of the world and an important field-to-store pest of pulse crops in Africa and Asia[6]. Females lay eggs on the pods or seeds. After hatching, the larva crosses the tegument and penetrates into the seed. Larval development occurs inside the seed at the expense of food reserves located in the cotyledons and the germ [7]. Grain legumes, especially cowpea (Vigna unguiculata (L.)Walp.) and Bambara groundnut( Vigna subterranea (L.) Verdc.),are very important in the diets of rural communities as rich sources of protein [8;9]in West Africa. Pigeon pea (Cajanus cajan (L.) Millsp.)has also become a very important grain legume used in human nutrition in this area. However, because of their high susceptibility to several storage pests, they are out of reach during a long period of the year, and their nutritive potential is therefore underutilized [10;3]. Many studies have shown that cowpea is the favored host plant for development of C. maculatus. However, it is possible that this pest could also develop on unusual host species such as Bambara groundnut and pigeon pea [11;3].Some plants that are known to be favorable to C. maculatus allow its development with varying degrees of success [12;3]. 

Therefore, it is necessary to examine whether C. maculatus, which is already a serious pest of cowpea, could also become a key pest of these legumes. Within the Papilionoideae, most hosts of C. maculates belong to the tribe of Phaseoleae and crops which are most severely infested, are found in the genus Vigna[11].[7] have shown that C. maculatus had a longer post-embryonic development on Flemingo congesta seeds than on cowpea. Within the genus Vigna, some cowpea varieties are more susceptible than others and therefore are more readily infested [12;13]. While this beetle is oligophagous, its development capacity in the seeds of legumes such as Vicia faba (L.) remains limited [1]. These plant species seem to contain substances that would block larval development of C. maculatus within the seed. These substances have an antibiosis effect on the growth of C. maculatus. They may also influence the speed of C. maculatus embryonic development. Understanding the conditions of developing a pest on a specific host is not only important for pest control, but also for the prediction and prevention of the emergence of new pests. Callosobruchus maculatus life cycle has four larval stages. The reproductive capacity and development of C. maculates have been the focus of much research, the results of which appear to depend on the geographical origin of the strains, the legume species, and cultivar of each host species [14;15]. However, data on the embryonic and larval development of C. maculatus are very scarce. Thus, the understanding of embryonic and post-embryonic development and the factors influencing them is a challenge that needs to be addressed for successful integrated pest management. This study is based on the premise that the secondary host plants could influence the larval and embryonic development of C. maculatus. The aim of this work was to investigate the influence of two secondary host plants (white and striped Bambara groundnut and pigeon pea) on the embryonic and larval development of C. maculatus.