Host Selection And Olfactory Learning Behavior Of Bactrocera Dorsalis To Several Host Fruit

The oriental fruit fly, Bactrocra dorsalis Hendel (Diptera, Tetriphitidate), is an important quarantine pest worldwide. In the last decade, it has dispersed all over the South and Southwest China and caused severe damage to fruit production. The potential distribution of this species may expand northward and to the larger area. B. dorsalis is mainly distributed in the Southwest and Southern China. The outbreaks in recent years seriously hampered the development of the local fruit industry. B. dorsalis, a polyphagous pest, has a potential large distribution area in the world-wide due to its wide range of host plants, high fecundity, and strong colonization ability.The objective of this study was to investigate1) the host selection of B. dorsalis for oviposition among bananas, navel orange, wax apple, apples, tomatoes, pears, and persimmons,2) the olfactory behavioral responses to bananas, navel orange, apples, pears, and essential oil of tangerine, navel orange, and lemon using four-arm olfactometer,3) the effects of larval feeding experience on host perference and fecundity of adult, and4) whether the linalool treatments on pupa lead to the olfactory memory of adults. The results are as following:1The host selection of several B. dorsalis populations for oviposition among host plantsThe first to third generations (F1-F3) of B. dorsalis reared on artificial diet and the fifteenth generation (F15) of that on bananas saw significantly different fecundity in devices containing seven fruits, respectively. The F15population laid averagely more eggs on seven fruits than did the F1-F3population. Meanwhile, F15population preferred to lay eggs on bananas and navel oranges. The number of eggs in devices containing bananas and navel oranges reached to229.66and213.33, respectively, which was1.7times more than average number of eggs laid by F1-F3population. Volatiles of the fruits are the main factors of inducing B. dorsalis to oviposit.The fecundity of F1-F3popualtion was the highest on bananas and navel oranges, the lowest on apples, tomatoes, pears, and persimmons, and the medium on wax apples. The period of feeding on artificial diet seemed to have a positively effect on fecundity of B. dorsalis on bananas and navel oranges. The Fl female adults laid only61.50eggs on average, but the F2and F3laid significantly more eggs. All results showed that bananas and navel oranges are the optimal hosts for B. dorsalis to oviposit and such preferences can be strengthened by feeding on bananas in advance for a long time.2Olfactory behavioral responses of B. dorsalis to volatiles of four host fruitsThe average residence time of B. dorsalis responding to volatiles of four host fruits were significantly different. It reached as long as3154.33s to navel oranges, followed by1956.67to bananas,1667.00s to apples, and1424.66s to pears. The frequency of residence time over120s was significantly higher when responding to navel oranges and bananas (4.67and5times) than apples and pears (0.33and0.67times). The average visit times to bananas, navel oranges, apples, and pears were8.67,6.75,4.67, and6.15, respectively. The selective coefficient of B. dorsalis to bananas (4.11) was significantly higher that that to navel oranges (2.84). In addition, both of these selective conefficients were significantly higher than that to apples and pears.3Olfactory behavioral responses of B. dorsalis to essential oil of three plantsThe average residence time of B. dorsalis responding to essential oil of navel orange (70.4s), tangerine (49.ls), and lemon (122.62) was significantly different from each other, indicating the essential oil of lemon is the most attractive to B. dorsalis, followed by, in order, that of navel orange and tangerine.4The effects of larval feeding experience on host perference and fecundity of adultB. dorsalis, fed by different fruits during larva stage, generally prefered laying eggs on bananas and navel oranges to apples and pears. The femal adults that laid the most eggs on each fruit were fed by the same fruit during larva stage, indicating the B. dorsalis can learn and remember the feeding experience of larva, which is able to affect the host selection of adults to oviposit.5The effects of pupal experience on olfactory memory of adultB. dorsalis individuals were treated with various concentration of linalool and ethyl benzoate at pupa stage. There was no significant difference between treatments and control in residence time of adults, emerged at the same time, responding to each compound, showing that the aduls can not memorize linalool and ethyl benzoate.