Methodology Development for Bt Rice (Cry1Ac) Effect Assessment on Non-target Arthropods

Abstract

To assess effects of Bt rice (Cry1Ac) for control Cnaphalocrocis medinalis on non-target arthropods, laboratory tests were conducted to evaluate the potential impacts of 1) Bt rice leaf expressing cry1Ac on development, survival, emergence and fitness of adult of non-target herbivores, Nilaparvata lugens, Oxya japonica and Scotinophara lurida, 2) Bt rice pollen on development, survival, emergence and fitness of adult of non-target pollen-feeder, P ropylea japonica, 3) prey fed on Bt rice leaf on development, survival, emergence and fitness of adult of non-target predator, Pirata subpiraticus and Pachygnatha clercki, and 4) Bt rice leaf on development, survival and emergence of N aranga aenescens close to the target pest species, C. medinalis, and on oviposition preference of C. medinalis. There were no significant differences in development, survival and emergence of O. japonica, S. lurida and N. lugens between Bt and non-Bt rice. Also, no significant differences were found in development and survival of P. subpiraticus and P. clercki feeding on N. lugens reared on Bt or non-Bt rice but tibia lengths of P. subpiraticus and P. clercki feeding on N. lugens reared on Bt rice were significantly longer than those feeding on N. lugens in non-Bt rice. There were no adverse effect on the development, survival and fitness of adult P. japonica after ingestion of Bt rice pollen expressing Cry1Ac. N. aenescens showed significant differences in development, survival and emergence rate between Bt and non-Bt rice. C. medinalis did not show oviposition preference between Bt and non-Bt rice. In a 2-year field study, a total 43 familes in 10 orders were identified from 64,099 collected insects and classified four guilds, Herbivores, Predators, Parasitoids, andDetritivores. Family richness, abundance and Shannons index of insects were very similar between Bt and non-Bt rice. However, significantly higher abundance was observed in the non-Bt rice in the herbivore in 2007, and predator, and Coenagrionidae, in 2008. A total 29 species in 23 genera and 9 families were identified from 4,937 collected spiders and both Bt and non- Bt rice fields showed a typical Korean spider assemblage. Species richness, abundance and Shannons index of spiders were very similar between Bt and non-Bt rice, although in 2008 significant difference was observed in the abundance of P. oculiprominens, T. maxillosa and P. clercki in the . P. oculiprominens and T. maxillosa were higher in non-Bt rice and P. clercki was higher in Bt rice. The results indicated that the transgenic Cry1Ac rice tested in this study had no significant adverse effects on the rice insect and spider community structure in rice fields and on the development, survival, emergence and adult fitness parameter of non-target arthropods and oviposition preference of the target species in the laboratory conditions. To suggest appropriate sampling methods, sampling plot size, sampling timing and sampling occasion for field assessment following experiments were conducted. The efficacy of two sampling methods, sweep net and suction, were compared to survey insect and spider community, species richness and diversity of spiders in rice fields of three different plot sizes, 270 m2, 1000 m2 and 3300 m2, throughout the rice growing season. Suction sampling captured more spider species and individuals than sweep net sampling, but insects were captured more by sweep net sampling. In this study, biodiversity of spiders did not increase with increase of plot size. The similarity of the community was higher between 1000 m2 and 3300 m2 than others. Thus it seems that 1000 m2 plot size test is resonable to detect Bt crop effects on arthropods community in rice fields. This study used cluster analysis with similarity of community to find appropriate sampling time and occasion, and sampling time were divided into five clusters with 65.6% similarity and these clusters generally corresponded to five rice growing stages in the fields.