Field biology and identification of fruit flies in the Western Cape Province

[摘要] ENGLISH ABSTRACT:Two fruit fly species, Ceratitis capitata (Wiedemann) and C. rosa (Karsch)(Diptera: Tephritidae) are known to attack deciduous fruit in the Western CapeProvince of South Africa. The relative abundance of these two pests was studied indifferent kinds of fruit throughout the year.To facilitate field monitoring, using the immature stages, morphologicaldifferences between larval instars of C. capitata and C. rosa were investigated.Morphological characters of the larvae, such as the spiracles (anterior and posterior),mouth hooks and oral ridges were used. Many of these characters are only suitable todistinguish between the second and third instar larvae as these structures are not yetdeveloped in the first instar larvae. Anterior spiracles were examined in terms of thenumber of tubules (papillae) and size or shape of the felt chambers. The number ofpapillae in both species was similar in the second and third instar larvae, but differedbetween the larvae of the two species (8-10 for C. capitata and 10-13 for C. rosa). Inboth species the felt chambers of the second instar larvae were narrow and elongatewhilst those of the third instar larvae were broad and short. The major differencebetween the mouthhooks of the two tephritids was the presence of a sub-apical tooth inthe third instar larva of C. rosa, being absent in the third instar of C. capitata.For the morphometric study, both laboratory-reared and field-collected specimenswere examined. Measurements of the body dimensions (length and width) and variousparts of the cephalopharyngeal skeleton (CPS) (mandible base, mandible length anddistance between the tip and notch) were recorded in all three instars of both C.capitata and C. rosa. The data were analysed using finite mixture analysis (FMA-N1)and Levene's test was used to test for homogeneity of variances. The results of these analyses were used to estimate the frequency distributions of the larval measurements.In some cases overlaps in distributions were evident and were resolved using the sameprogram, finite mixture analysis (FMA-N1), based on the probability of the overlappingmeasurements belonging to the designated instar (i.e. the one with highest probability).Determination of growth ratios suggested an approximate conformation to Dyar's rulethereby disputing the possibility of any hidden instar. However, in most casesmeasurements of the field samples did not conform to Dyar's rule.For the larval instars of C. capitata and C. rosa with overlapping morphologicalfeatures, the morphometric approach as a distinguishing tool was demonstrated. In thefield survey, the relative abundance of C. rosa at all experimental sites was very low inboth orchards and adjacent vines. This suggested that this pest was either not a threatin these sites (crops) or the monitoring procedures applied, should be revised. Trapcatches indicated high levels of infestation by C. capitata on some sites and lowinfestation levels at others. On the site with the highest population levels, activity peaksin the orchards did not co-incide with those in the adjacent vineyards. This suggestedthat these vineyards could be alternative hosts for fruit fly after the fruit in the orchardshave been harvested.Forced oviposition (in vitro) studies indicated that Colombard (grown inSimonsvlei) was the most suitable host for survival of C. capitata. Other wine grapecultivars such as Chardonnay were also suitable for the total larval development of C.capitata.

[发布机构] Stellenbosch University