Trichogrammatoidea bactrae (Hymenoptera: Trichogrammatidae): a potential biocontrol agent of rice leaf folder

Rice leaf folder, Cnaphalocrocis medinalis is a major pest, in many rice growing areas of Sri Lanka. Biological control of this pest is encouraged due to ill effects of insecticide application on rice ecosystem. Use of egg parasitoids is advantageous over larval and pupal parasitoids, as they could destroy pests at the egg stage. Trichogrammatoidea bactrae present in rice fields in Sri Lanka, is an egg parasitoid of rice leaf folder. This study was conducted to assess the potential of T. bactrae as a biocontrol agent for the management of rice leaf folder. T. bactrae was reared on Cocyra cephalonica and its fecundity, longevity and parasitism were assessed. Acceptance of stored host eggs and parasitoid emergence from stored parasitized eggs were examined. Dispersal ability of parasitoid was also examined. T. bactrae adults showed a mean longevity of 7.9 days (range 1-15 days) and laid 55 eggs / female during first 5 days; of which, 56 % of eggs was laid on the first day. There was a significant reduction (F=5.26; df=14; 89; P< 0.001) in parasitism, 66-35 %, with increasing number of generations on C. cephalonica. Parasitism steadily decreased as the number of generations increased. Acceptance of C. cephalonica eggs varied significantly with temperature (F=187 df=1; 126 P<0.001). Mean acceptance at 4 and 8ºC was 30 and 42 % respectively. Acceptance also significantly varied with the duration stored (F=385; df=6; 126; P<0.001). Parasitized eggs of T. bactrae could be successfully stored under low temperature (4ºC) up to 40 d. Over 80 % parasitism was achieved with 150 parasitoids released within 25 cm radius circle. Hence, T. bactrae is a promising candidate to be promoted as a biocontrol agent of C. medinalis.

Tropical Agricultural Research Vol. 26 (3): 537 - 546 (2015)