Assessment of the egg parasitoid guild of rice leaf folder, Cnaphalocrocis medinalis (Guenee): a search for biocontrol agents

Biological control of rice leaf folder (RLF), Cnaphlocrocis medinalis by augmentative release of egg parasitoids has been suggested. This study was conducted to assess the egg parasitoid guild associated with the RLF and to determine their parasitism levels under local conditions. A survey was conducted in three districts at 14 sites using 16 fields where rice was cultivated under conventional, pesticide free and organic farming practices. RLF eggs were collected and incubated at room temperature with 60 % RH under natural daylight in the laboratory. The emerging parasitoids were identified and their parasitism levels were calculated. Four egg parasitoid species: Thoichogrammatoidea bactrae, Troichogrammatoidea nana, Trichogramma sp. and Lithromeromyia sp. (Hymenoptera: Trichogrammatidae) were found parasitising RLF eggs. These species collectively parasitised 17 % of RLF eggs and the level of parasitism significantly varied between 0 and 57 % among sampling sites. Mean parasitism in conventional and pesticide free fields were 1.62 +/- 0.81 % and 24.39 +/- 16.8 %, respectively, which was significantly different. T bactrae was the most prevalent parasitoid species, which was found in nine sites, while T nana and Lithromeromyia sp. were found only in one site. Trichogramma sp. was found in four sites. Mean parasitism caused by T bactrae, T nana, Trichogramma sp. and Lithromeromyia sp. were 8.2 +/- 5.7 %, 15.2 %, 3.7 +/- 1.3 % and 2.5 %, respectively. The parasitoids did not affect beneficial arthropods such as spiders and coccinellids. The results suggest that T bactrae is a potential egg parasitoid of RLF to manage RLF populations in local rice fields through augmentative release.