Ovipositor morphology and host relations of the Bactrocera tau complex (Diptera: Tephritidae) in Thailand

Abstract

The taxon, Bactrocera tau, is a complex of fruit flies that infest fruits of many species in the family Cucurbitaceae as well as fruits from very different plant families in southeast Asia. Past mitotic karyotype studies of B. tau flies from different geographic location- and/or host-associated populations indicate there are nine forms present within the taxon in Thailand, which have been designated as B. tau forms A to I. In this study, ovipositor morphology was compared among seven members of the B. tau complex using scanning electron microscopy. The flies could be placed into two main groups based on the shape of the aculeus apex. The first group comprised B. tau forms C and I which have trilobed aculeus apices. The second group included B. tau forms A, D, E, F and G, all of which have single-pointed apices. The latter five forms were further divided on the basis of the sharpness of the aculeus apex into "medium" (A and E), "sharp" (D and G) and "blunt" (F) apices. Host fruit associations, fly aculeus apex shape and geographical region were overlain onto a molecular phylogeny previously published for the B. tau group in Thailand. Cucurbitaceae fruits appear to be ancestral hosts for the B. tau complex whereas the use of fruits of other plant families appeared late in the evolutionary history of this group. Forms with trilobed and singlepointed aculeus apices separated early in B. tau evolutionary history, but the split does not seem host related. Flies with medium, sharp and blunt, simple-pointed aculeus apices showed no evident associations, being randomly distributed across the phylogenetic tree. Bactrocera tau form A which infested fruits of nine Cucurbitaceae species was found in all five surveyed regions, whereas each of the other forms, which were restricted to 1-3 fruit species, were found in 1-2 regions.