Oviposition plasticity in Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae).

The oviposition plasticity (term used here to refer to the phenomenon whereby some insects reduce egg laying in poor conditions and increase it when conditions improve) of Sitophilus zeamais, one of the most serious insect pests to maize during grain storage, was investigated in different food resources. Whether such oviposition plasticity exists, it can be investigated by finding if more eggs are subsequently laid by insects previously kept on unfavourable environment than by insects previously kept on favourable environment. Virgin male/female pairs of maize weevils were raised on different feeding treatments consisting of maize grain (favourable environment) or maize flour (unfavourable environment). After 1 or 3 weeks exposure, all male/female pairs were transferred to new maize grains for a week, then the adults were removed. The maize were kept for 7 weeks and the emerged adults were sieved off and counted (to give a measure of productivity), sexed and weighted. Emergence of adult weevils was higher when parents were previously kept on flour maize than when parents were previously kept on maize grain. The mean weight and the sex ratio (males/100 females) of the emerged adults did not differ between treatments. These results suggested that S. zeamais have plasticity and ability to successfully modify their oviposition behaviour to correspond to change in the experimental situation.