Field evaluation of Trichogramma strains collected from Myanmar for biological control of Asian corn borer, Ostrinia furnacalis (Guen′ee) (Lepidoptera: Crambidae) and sustainable maize production

Trichogramma (Hymenoptera: Trichogrammatidae) egg parasitoids are successfully used for biological control of Asian corn borer, Ostrinia furnacalis (Guene ' e) in China. This pest has become increasingly problematic in Myanmar and surrounding countries. To determine the optimal number of releases, release density and select the most effecive parasitoid, two strains of Trichogramma ostriniae (Pang and Chen) and one Trichogramma dendrolimi (Matsumura), originating from Myanmar, were assessed under field-cage conditions in 2020-2021. Three release densities, 50,000 wasps/ha (low), 100,000 wasps/ha (medium) and 200,000 wasps/ha (high), were tested with three releases at weekly intervals during tasseling stage. The highest egg parasitism rate was achieved by T. ostriniae from Yatsawk, Southern Shan State (overall 89%), followed by T. dendrolimi from Yatsawk and T. ostriniae from Taungyi (67%). The kernel weight of maize plots treated with the T. ostriniae from Yatsawk was 1.2-1.4 times higher than values for the other two tested strains and significantly increased yield by 60% over control plots. Trichogramma ostriniae from Yatsawk overall showed the best performance, and may be considered the most promising strain for biological control of O. furnacalis in Myanmar. Two-and three-inundative releases substantially reduced plant damage (60-80%) and yield loss (50%) over control plots. The highest cost-benefit ratio (1:31) was found for two releases of the medium release density. Two releases with either medium or high release density was optimal to achieve high yield and best net return. Our results facilitate the initiation of a biological control program to improve maize production in Myanmar.