Geographic variation and host utilization pattern of Bactrocera philippinensis Drew and hancock and B. occipitalis (Bezzi) (Diptera:Tephritidae) in seledcted areas of the Philippines

Laboratory studies were carried out (a) to evaluate taxonomic characters that can improve the differentiation between the two fruit fly species, b) to determine host plant preference of the two species, and c) to evaluate the suitability of the different host fruits to the two species of fruit flies. A field survey was also conducted to obtain observaitons on the population abundance, and host plant use of Bactrocera philippinensis and B. occipitalis in Laguna and Zambales. These studies were conducted to understand and differentiate the biology and ecology of the two fruit fly species in the context of posibly resolving the difficulty in taxonomically differentiating the two species following the currently acceptable Iwahashi (1999) criteria. The length of the male aedeagus and wing type were evaluated for its value as a taxonomic character to distinguish B. philippinensis from B. occipitalis. While these two characters were able to cluster adult individuals into a B. philippinensis group and a B. occipitalis, a few individuals were still classified as hybrids. The question of whether these morphological characters provide a reliable indication of a reproductive gap between the two species warrants further investigation. Field survey showed that the population of B. philippinensis is higher than the population of B. occipitalis in most of the sampling dates in all study sites. Intermediate forms of fruit flies or Iwahashi 'hybrids' were present all year round in all study sites but their numbers were consistently low. Host utilization pattern of fruit flies seem to be correlated with seasonality of fruits since some of the host fruits, (i.e., mango, santol and star apple) are seasonally available and often infested by fruit flies. The field survey clearly showed that there was significant overlap in the host range of the two species, and that there is no indication of distinct host specialization by either b. philippinensis or B. occipitalis. Populations, of B. philippinensis collected from Los Baños (UPLB Orchard), Calamba (Sirang Lupa), and Zambales and B. occipitalis from Laguna de Bay (Pasong Kipot), were used to determine the host preference of the two fruit fly species on four host fruits. The result of the pair-wise choice test showed that preference varied across local populations of B. phlippinensis and B. occipitalis in the study areas. However, in most cases guava appears to be often preferred for oviposition by the two species as indicated in terms of the mean number of egg clutches laid per female and the total number of eggs deposited on the subject fruits. Larval performance (host fruit suitability) of B. philippinensis from Los Baños (UPLB Orchard), Calamba (Sirang Lupa), and Zambales and B. occipetalis from Laguna de Bay (Pasong Kipot) varied on the four host fruits that were evaluated. The most suitable fruits for Zambales population were papaya and guava in terms of larval survival to adult stage while mango was the most suitable for UPLB Orchard population, and starfruit for the Sirang Lupa population. The mean development time to adult stage was generally about 5 days longer in B. occipitalis in Pasong Kipot population compared with the B. philippinensis population from UPLB Orchard. The result of the comparative studies indicating the absence of detectable differences in the host use, oviposition preference, larval performance on selected fruits, and the presence of Iwahashi (1999) 'hybrids' regularly in the field in all study areas do not support the widely held interpretation that a reproductive gap exists between B. philippinensis and B. occipitalis.