Abstract

For many years it has been known that cannibalism is a natural phenomenon in insects and has been documented in many insect orders including Lepidoptera. The present study was conducted to determine cannibalistic behavior amongst same-age 2nd, 4th and 5th instar stages of larval Spodotera frugiperda (FAW), Spodotera littoralis (CLW) or when both are combined together under laboratory conditions. The FAW larvae had a higher predatory ability than CLW larvae. However, when both same stage of FAW and CLW are combined together, the survivability and predation ability of FAW larvae were higher than for CLW. Necrophagy in FAW became more frequent as the larvae developed from young to older larvae (L2 to L4 and L5, with mortality of 24.7, 42.7 and 52.6%, respectively. CLW larvae are rarely fed entirely on their fellow larvae. Mortality due to necrophagy in CLW was highly significant among the different stages. Mortality rate due to necrophagy amongst tested stages of the 2nd, 4th and 5th instars was 1.33, 14.7, and 12.1%, respectively. Rearing FAW and CLW in laboratory shows that larval cannibalism is necessary for FAW, but not for CLW. Also, the cannibalistic behavior consequently affected the adult yield in each group of tested larvae and was stage-dependent. The percentage of emerged moths was greatest amongst CLW larvae of tested stages where no larval cannibalism was observed. The adult’s yield of FAW was lower when reared alone and lowest when combined with CLW indicating that all CLW and some FAW larvae were cannibalized.

Key words: Cannibalistic behavior, fall armyworm, cotton leaf worm, larval survivorship, adult yield.