Egg cannibalism in Helicoverpa armigera on sorghum and pigeonpea

Egg cannibalism by Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) larvae was studied in the laboratory and in the field. In laboratory experiments, first instars were exposed to increasing densities of H. armigera eggs on sorghum, Sorghum bicolor (L.) Moench, and pigeonpea, Cajanus cajan (L.) Millsp. The number of eggs eaten per larva increased significantly as egg availability increased on both sorghum and pigeonpea. In small cages 21-37% of eggs were eaten on sorghum, 4-12% on pigeonpea. Plant feeding declined significantly on both sorghum and pigeonpea as egg density increased. Cannibalism was greater on sorghum than on pigeonpea while plant feeding was greater on pigeonpea than on sorghum. Only around 8% of eggs were eaten in larger cages with sorghum. The response to increasing egg availability in all experiments was linear. Immunoassay with an anti-vitellin monoclonal antibody showed that egg cannibalism occurs on pigeonpea under field conditions. Seven percent of all larvae had egg protein in their gut. Cannibalism may make a significant contribution to H. armigera population suppression.