Seasonal Occurrence of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), a Parasitoid of Bactrocera correcta (Bezzi) (Diptera: Tephritidae) in a Guava Orchard in Central Thailand

Sangvorn Kitthawee

ABSTRACT: Relationships between the parasitoid, Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), its fly host, Bactrocera correcta (Bezzi) (Diptera: Tephritidae), and the host plant, Psidium guajava L., are described. The abundances of fruit and fruit flies per fruit were correlated with seasonal changes in the mean maximum monthly relative humidity. The analysis model was: fruit flies per fruit = 0.892(monthly mean max %RH) - 79.753. The mean maximum temperature over the month before fruit harvest was correlated with parasitoids per fruit (r = 0.530; P 0.05). Both the fruit and fruit fly abundance were found to influence parasitoid number. The regression equation is described by Ln (parasitoid no.) = 1.673 + 0.029 (fruit no.) + 0.238 Ln (fruit flies per fruit). In nature, the ratio of female : male parasitoids was 4:3. Larger fruits may provide more nutrients, produce larger host flies and in turn, affect the parasitoid size. D. longicaudata females were produced from larger fly hosts whereas males were produced from smaller fly hosts. Larger female parasitoids produce more offspring than smaller females. The production of more parasitoids, as observed, may provide better biological control.

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

Received 6 Jul 1999, Accepted 31 Mar 2000