Impact factors of superparasitism by Coccophagus japonicus and its effects on the offspring

This study aims to clarify the factors influencing the superparasitism by parasitoid wasp, Coccophagus japonicus and its impact on the development and reproduction. The observations were conducted under various indoor conditions of different parasitoid densities, female residence time, intervals between wasp releases and host stages. Also, the development, longevity, adult emergence and body length of the female wasps were assessed under high superparasitism condition (1 parasitoid: 5 scales) at four different stages of host, Parasaissetia nigra, including the 2^nd and 3^rd instar nymphs, 1-2-day-old adults (initial adults) and 10-11-day-old adults (brown adults).The result showed that parasitoid density, female residence time, interval between wasp releases and host stage all were factors influencing the superparasitism of C. japonicus. The superparasitism rate of C. japonicus decreased with the decrease of parasitoid density. The highest superparasitism rate (91.03%) was found when the wasp-host ratio was 1 : 5, and the lowest superparasitism rate (11.61%) was found when the wasp-host ratio was 1 : 30. When the interval between wasp releases was 6 days, the superparasitism rate was the highest (57.72%). When the female residence time of C. japonicus was in the range of 0~48 h, superparasitism rate increased with residence time increasing, and the superparasitism rate was the highest (30.41%) at 48 h. The effect of host stage was also observed, and the highest superparasitism rate (54.40%) was found when using 3^rd instar nymphs P. nigra as hosts. In general, compared with the control group, C. japonicus during superparasitism had longer developmental time, shorter longevities, shorter body lengths and more adult emergence. Ecpecting that under high superparasitism rate, when the host was the 2^nd instar nymphs of P. nigra, the development period of C. japonicus was shorter than that of the control group, and when the host was the initial adult of P. nigra, the number of adult emergence was less than that of the control group. Therefore, the study showed that the parasitoid density, female residence time, interval between wasp releases and host stage were important factors influencing the superparasitism by C. japonicus. Superparasitism led to extended development periods and reduced quality of C. japonicus, although the probability of obtaining offspring from the host was slightly increased.