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Factors Determining the Rate of Parasitism by a Parasitoid with a low Fecundity, Chrysis shanghaiensis (Hymenoptera: Chrysididae)

1987; Wiley; Volume: 56; Issue: 3 Linguagem: Inglês

10.2307/4964

1365-2656

Yoshihiro Yamada,

Agricultural pest management studies

SUMMARY (1) The mechanism determining the rate of parasitism in the population interaction between the oriental moth, Monemaflavescens Walker (Lepidoptera: Heterogeneidae), and its cocoon-attacking parasitoid, Chrysis shanghaiensis Smith (Hymenoptera: Chrysididae), was analysed based on data collected in the field during the period 1978-81. (2) Both the host and the parasitoid had one and partly two generations a year. The parasitism by the chrysidid wasp reached 60-70% in the first 2 years, but it did not exceed 50% in the last 2 years. The distribution of oviposition holes among host cocoons (one hole usually indicates that one egg was laid inside the cocoon) showed a high uniformity in the first generation, whereas in the second generation the uniformity was decreased. (3) The lower a host cocoon was placed on trees, the more likely it was to avoid parasitization. The rate of parasitism among cocoons placed near the ground, however, increased with the increase of the rate among the remaining cocoons. In addition, the proportion of the cocoons near the ground in the whole cocoon population was usually low. Thus, this spatial refuge was not important as a determinant of the rate of parasitism. (4) Early-spun cocoons of the second generation were more likely to be parasitized than late-spun ones. The proportion of second generation cocoons vulnerable to parasitoid attack due to early spinning was estimated on the basis of the distribution of the oviposition holes. The proportion ranged from 24-2 to 65-6%. (5) The value of the 'area of discovery' varied greatly depending on the generations, and did not show a significant relationship with the parasitoid density. On the other hand, the average number of oviposition holes made by each female parasitoid increased as the rate of female parasitoids to hosts increased, and the correlation between the two was very