Mass rearing and field releases of predatory earwigs, Euborellia annulata for the management of Asian corn borer, Ostrinia furnacalis Guenee

The paper reports on the mass production technique for the predatory earwig, Euborellia annulata and field evaluation of its effectiveness for the management of Asian corn borer (ACB), Ostrinia furnacalis Guenee, the most destructive insect pests of corn in the Philippines. The earwig was successfully mass-reared on factitious diet using a combination of dog food and corn cob at 1:1 ratio. With this technique, the cost of production is six centavos per earwig. Earwig reared on this diet has a life cycle of 110 days from eggs to death of an adult and females laid an average of 4 batches totalling to 216 eggs. The percentage survivors from egg to adult from four batches is 90%. The sex ratio of the offspring was 1 male to 6 females based on 60 mothers. The adult has a total longevity of 74 days. Small and large-scale field evaluations were conducted to determine the effectiveness of this predatory earwig species in controlling ACB as compared to control and to other treatments on three corn varieties, namely: asukar and lagkitan for green corn (GC) and IPB VAR-1 for open pollinated variety (OPV). The earwig (1 earwig/sq.m) were released 2 times at 32 and 46 days after planting (DAP) in open pollinated variety while 3 times at 25, 32 and 39 DAP in green corn. Monitoring of ACB-damaged plants was done weekly before and after earwig releases. Yield data was taken at harvest and converted to tons/ha. In OPV, 20,000 earwigs are needed in controlling ACB while 30,000 earwigs in GC per hectare per cropping season. In small scale experiment planted with green corn, treatments with the earwig releases, only T1 gave 41% higher in yield as compared to control. The increase in net income both in asukar and lagkitan was 59 and 61%, respectively as compared to using insecticides (T4). In a large scale field experiment, both in asukar and lagkitan, the percent plant with ACB damage in the treatments with earwig only (T1), earwig plus detasseling (T2), earwig supplemented with microbial (Bacillus thuringiensis var. Kurstaki, T3) and with insecticide applications (T4) were significantly different from the control. The use of earwigs in controlling ACB in asukar gave 69% and 59% higher in net income as compared to control and to using insecticides, respectively. On the other hand in lagkitan, the net income was 87 and 61% higher compared to control and to using insecticides, respectively. The reduction in cost of production due to reduced insecticide applications was P200 to P600 per hectare. Based on 600,000 hectares planted with corn and applied with insecticides, the potential savings on insecticide applications for this area alone will be P120 million if the technology could be promoted and adopted by the corn farmers