Mortality factors of eggs of Leptocorisa chinensis (Hemiptera: Alydidae) in rice fields.

To clarify factors causing mortality of Leptocorisa chinensis Dallas (Hemiptera: Alydidae) eggs in rice fields, sentinel egg masses were exposed for seven days in two rice, Oryza sativa L. (Poaceae), fields. An insecticide was sprayed to remove natural enemies in one-half of each field before exposing egg masses to predation. An egg mass containing 14 eggs was glued to a plastic label, and 21 egg masses each were placed in the sprayed and unsprayed control plots. During exposure, the number of hatched and missing eggs was observed daily. Egg predators were sampled in the fields before and after insecticide application. After the egg masses were retrieved from the fields, mortality factors of the unhatched eggs were assessed in the laboratory. The mean number of hatched and missing eggs was not significantly different between the sprayed and control plots in field A. In field B, however, the numbers were significantly different. The percentage of missing eggs in damaged egg masses ranged from 80 to 100%. In the laboratory, we observed that feeding marks caused by the grasshopper Conocephalus chinensis (Redtenbacher) were similar to those on the eggs exposed in the rice fields. The density of C. chinensis was low in control plots of field A. In contrast, the density was high in those of field B. These observations suggest that the density of egg predators, e.g., C. chinensis, is a mortality factor of L. chinensis eggs in rice fields.