 BackResearch Article ScienceAsia 23 (1997): 013-022 |doi: 10.2306/scienceasia1513-1874.1997.23.013
CHOICE OF HOST INSTAR IN GONIOZUS THAILANDENSIS GORDH & WITETHOM (HYMENOPTERA: BETHYLIDAE), A GREGARIOUS ECTOPARASITOID OF A SAPODILLA FRUIT BORER, PSEUDOCEROPREPES CF. NAGA (LEPIDOPTERA: PYRALIDAE)
BOONGEUAW VAJARASATHIRA1 AND LOUIS P. LEBEL2ABSTRACT: Goniozus thailandensis Cordh & Witethom is a gregarious larval ectoparasitoid of sapodilla fruit borer, Pseudoceroprepes cf. naga, in southern Thailand. The host instar preference and suitability for G. thailandensis oviposition was simultaneously tested in choice and no-choice situations. In the no-choice situation, 4th and 5th instars were 4.3 times more likely to be parasitized than 3rd instars. The differences, however, were not significant. The presence of alternative instars had no significant effect on parasitoid choice behavior. The overall parasitization rates observed (10%) were low but comparable to that in the field. The trends, however, suggested a preference towards later instars over earlier instars. Two, alternative, explanations for the negative test result for behavior choice in G. thailandensis are discussed. Firstly, the result could be dismissed because of low power. Secondly, the differences in probabilities of parasitization between 3rd, 4th and 5th instar hosts in no-choice experiment are not due to behavioral choice, but reflect differences in handling times or ease of oviposition among host instars. Larger, 5th instar hosts produced more cocoons and adult progeny than smaller, 3rd and 4th instar hosts. Development time, however, was, on average, shortest in 4th instar hosts. Slow development time ( 1 Department of Biology, Faculty of Science, Prince of Songkla University Haad Yai, Songkhla 90112, Thailand. Received September 27, 1996
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20d) was more common in females than males. Developmental flexibility would allow G. thailandensis to survive in the field where host instar composition is seasonally variable. 
