Larval survival and ovipositional preference of the Asian corn borer, Ostrinia furnacalis Guenee, for some alternate host plants at different growth stages

Determining the alternate host plants of the Asian corn borer (ACB), Ostrinia furnacalis (Guenee), is essential in designing appropriate insect resistance management strategies for Bt corn. Such alternate host studies should be supported with data on the behavior of the ACB on those plants. This study aimed to determine the larval survival and ovipositional preference of ACB for some selected alternate host plants at different growth stages. Twenty-one host plants were maintained in three screencages at IPB [Institute of Plant Breeding] Sampaloc area enclosed in nylon net, each screencage serving as one replicate. The growth stages of the plants used were 30,45,60,75 and 90 days from planting. For ovipostional preference, male and female laboratory reared mated adults were released inside the three screencages. After two days, eggmasses were counted on all the plants. For larval survival, five third instar larvae were infested on each host plant and dissection of the test plants was done and two weeks after infestation to count the number of larvae that survived. Results showed that out of 21 host plants, three hosts were found to have eggmasses. Florida napier (75 DAP) and native napier (90 DAP) had the highest eggmass counts, with mean of 2.68 per plant. For larval survival, pupae and larvae were recovered from 15 host plants. Only the Florida napier had larvae collected from plants representing all age groups. The highest number of larvae collected was from native napier (90 DAP), and pupae from IPB Var 1 (45 DAP) and Florida napier (75 DAP and 90 DAP). The results suggest that the most preferred alternate host plants for oviposition were Florida napier and native napier. More larvae also survived on these two host plants. These alternate hosts were also found abundant in almost all major corn growing areas in the country (Lit and Fernandez, 2006). ACB larvae also preferred to feed on these alternate host plants. Under field conditions, it is possible that ACB larvae can also grow on these alternate host plants. Depending on the availability of food resources on when corn plants are not available, larvae may transfer to other hosts to survive. This implies that ACB can support its growth and development on these several alternate host plants. Larval movement and behavior on the alternate hosts need further investigation. It is possible that in the absence of corn in the field, the ACB will try to search for other food sources in order to survive. Thus, present views on the dynamics of ACB populations and the changes in the frequency of resistance-associated alleles therein may change. This also challenges the old view that only adult moth does the selection in the field. In turn, these implications may necessitate appropriate modifications of prescribed IRM strategies.