Bioecology of oriental fruit fly (Bactrocera dorsalis Hendel) on mango (Mangifera indica L.) in orchards under four different management practices

An Oriental fruit fly, Bactrocera dorsalis Hendel, is one of the most problematic tephritid fruit flies due to the severe damages caused to commercial fruits such as mango (Mangifera indica L.). However, the information on biology and ecology of this tephritid species particularly on mango variety is still lacking. Thus, this study aimed to investigate its infestation level through damaged mango fruits collection during mango fruiting season from four Chokanan mango orchards with different management practices in Jitra, Kedah (organic orchard), Bumbong Lima, Penang (unmanaged orchard), Bukit Changgang, Selangor (Good Agricultural Practices orchard) and Pulau Gadong, Malacca (conventional orchard). In addition, population fluctuation of B. dorsalis in the same mango orchards was conducted using methyl eugenol traps from mango flowering stage until harvesting stage. Moreover, the life table and demographic parameters from three cohorts of B. dorsalis eggs as well as the oviposition behaviour and offspring of B. dorsalis females on three different Chokanan mango ripening stages (i.e. unripe, ripe and fully-ripe) at five replication were determined in the laboratory. Results show the highest fruit infestation rate was recorded in Bumbong Lima (93.09±9.00 pupae/kg) due to no proper integrated control of fruit flies was conducted whilst Jitra showed the lowest infestation rate (10.74±1.25 pupae/kg) due to better control of fruit fly populations. Among the total of 5,229 Bactrocera pupae collected from infested fruits and 33,467 male flies collected from methyl eugenol traps, B. dorsalis showed significantly the highest numbers (P<0.05) compared to B. carambolae in all locations indicating that it is a dominant species and a major fruit fly pest of mango in Malaysia. Bactrocera dorsalis populations show similar fluctuation trends in most locations which the flies number start to increase in week 8 to 10 and peak numbers were recorded in week 14 to 16 because at this point the fruits reached the matured and ripe stages, which the most favourable stage for B. dorsalis females to lay eggs. Monthly relative humidity contributed significantly towards the population fluctuation of B. dorsalis in Pulau Gadong, Bumbong Lima and Jitra. However, only rainfall contributed significantly towards the population fluctuation of B. dorsalis in Bukit Changgang. Both abiotic factors are closely related to the B. dorsalis pupae development and adult emergence which they depend on the moist condition in soil and air. Age-specific survival (lx) indicated that 22.33% B. dorsalis eggs successfully reached to adults. The highest mortality recorded was in the 1st instar larvae (48.59%) with K-value of 0.289 and the pattern of survivorship curves falls in type III. This high mortalities may be regarded as the key factor regulating the population size of B. dorsalis. Age specific fecundity (mx) showed the earliest egg laying on day 35 and the last female died on day 69. The female laid on average 410.0±61.22 eggs. The intrinsic rate of natural increase (rm) was 0.06 per female per day with mean generation time (Tc) of 46.39 days. The net reproductive rate (Ro) was 13.68 female offspring per female. Doubling time occurred in 12.38 days. This showed that the population of B. dorsalis has rapid buildup in short period of time. Fully-ripe mango was relatively preferred by B. dorsalis females to visit and oviposit eggs followed by the ripe mango in no-choice and choice experiment. In contrast, unripe mango was the least preferred for eggs oviposition by B. dorsalis in both experiments. This indicated that the fully-ripe stage is more susceptibility in terms of fruit characteristics and nutrient contents.

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