Laboratory evaluation of density relationships of the parasitoid, Spalangia endius (Hymenoptera: Pteromalidae), with two species of tephritid fruit fly pupal hosts in Thailand

Sangvorn Kitthawee,* Kamolwan Sriplang, Warren Y. Brockelman and Visut Baimai

ABSTRACT: Laboratory experiments were performed on the parasitoid, Spalangia endius Walker, attacking the fruit fly pupal hosts, Bactrocera correcta (Bezzi) and B. dorsalis (Hendel), to determine the effects of parasitoid age, pupal age and density of both parasitoids and pupae on attack rates. Spalangia endius females attack at peak rates at approximately 3 d of age. The mean numbers of host pupae attacked per female parasitoid were 8.42 0.26 for B. correcta and 7.37 0.38 for B. dorsalis, for parasitoids aged 1–7 d. The rate of parasitism of B. dorsalis declined to below 50% by day 7 of pupal age, but that of B. correcta remained high (> 90%). The
experiments on varying host density determined that the numbers of pupae parasitized increased with host density, but the percentage parasitism declined, or was inversely density dependent. The results suggested that female S. endius exhibited a Type II functional response. The ovipositional behavior of the parasitoid on the two species of pupal hosts was random. In the experiments on variable host (or parasitoid) density, the percentage parasitism in B. correcta was significantly higher than that of B. dorsalis at all densities (paired ttests, p < 0.001). The oviposition efficiency of S. endius on B. correcta declined with parasitoid density, and can be described by the regression: A = 0.38 – 0.21 log P (F = 8.39, df = 1,10, p < 0.05, r² = 0.46) where A represents the area of discovery and P is number of parasitoids searching. However, searching efficiency of S. endius on B. dorsalis was lower and relatively constant with parasitoid density: A = 0.18 (F = 1.03, df = 1,10,
p = 0.33, r² = 0.09). These results suggest that host and parasitoid densities play an important role in the attack rate of the parasitoid, S. endius and that it may be more effective in biological control of tephritid fruit fly, B. correcta than of B. dorsalis.

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Department of Biology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand.

* Corresponding author, E-mail: grskt@mahidol.ac.th

Received 25 Mar 2004, Accepted 13 Aug 2004