Studies on population ecology and biological control by parasitoids of Liriomyza trifolii (Burgess)

The American Serpentine Leafminer, Liriomyza trifolii (Burgess), was first observed in 1990 at Hamamatsu in Shizuoka Prefecture in Japan. The distribution of L. trifolii has been spreading in Japan and this pest has become one of the most difficult pests to control on many kinds of crops, such as tomato, celery, gerbera and chrysanthemum. Since L. trifoUi is an exotic insect, its population ecology in Japan is unknown so far. But it is known that the population of L trifolii in Japan has the strong pesticide resistance against many insecticides by nature. And also, the introduction of pollinating insects, Bombus terrestris, on tomato has become popular as a labor-saving technique among growers, so the applications of insecticides in tomato greenhouses are restricted. These situations demand the development of control methods that can substitute for chemicals against L. trifolii, so these studies deal with the population ecology of L trifolii and the biological control by the imported parasitoids, Diglyphus isaea (Walker) and Dacnusa sibirica Telenga, against L trifolii 1. The effects of temperature and host plants on the population growth of L. trifolii were studied in the laboratory. The estimated threshold temperature for eggs, larval and pupal development on kidney bean were 8.0, 8.9 and 10.1degC, respectively. The total effective temperature for all stages was 257 degree-days. L. trifolii was reared at 25degC on kidney bean, pak-choi, tomato, cherry tomato, celery, gerbera, chrysanthemum and melon, and at different temperatures on tomato. The combined egg and larval development time varied from 6.5 days on kidney bean to 9.7 days on chrysanthemum. The fecundity of female adults varied from 54.7 eggs on tomato to 637.7 eggs on pak-chol The pupation rates at 25deg C varied from 56.2% on melon to 97.8% on kidney bean and were significantly different between crops. The adult emergence rates varied from 82.8% on celery to 96.5% on tomato. There were no large differences in the mean generation time between crops. Large differences in the net reproductive rate were found between crops, ranging from 25.21 on tomato to 271.99 on pak-choi. The intrinsic rates of natural increase on kidney bean, pak-choi, tomato, cherry tomato, celery, gerbera, chrysanthemum and melon were 0.2384, 0.2268, 0.1607, 0.1684, 0.2008, 0.1866, 0.1709 and 0.1429, respectively. The reproductive rates per day varied from 1.269 on kidney bean to 1.154 on melon. The hatchabilities on tomato were not significantly different between different temperatures, but the pupation rates and emergence rates were significant different between temperatures. The female fecundity varied from 3.3 at 15degC to 29.4 at 25degC, and female longevity was negatively correlated with temperature. The mean generation times varied from 55.85 at 15degC to 14.27 at 30degC. The net reproductive rate was 25.21 at 25degC, and the intrinsic rates of natural increase at 15degC, 20degC, 25degC and 30degC were -0.0042, 0.0655, 0.1607 and 0.0995, respectively. The population growth rate of L. trifolii was highest at 25degC. And also, close agreement between the density of L. trifolii predicted from a simulation model including the parameters elucidated in this study and the density observed on cherry tomato in a greenhouse was obtained. 2. The dispersal and the seasonal prevalence of occurrence of adults of L trifolii in fields were studied using yellow sticky traps. The capture of L. trifolii adults on traps was observed from the end of February to the middle of December, peaks of the occurrence were observed on June or July. Yellow sticky traps were placed horizontally and vertically near an eggplant greenhouse severely infested by L. trifolii in order to investigate the dispersal of L. trifolii adults. The number of adults captured by the traps placed vertically 0.5 - 5.5 m above the ground decreased with increased trap height. The number of