| The apple buprestid beetle, Agrilus mali Matsumura(Coleoptera, Buprestidae), is an important wood-boring insect causing significant damages to apple trees. Its larvae gnaw into the bark phloem where they can feed and develop into overwintering stages. Its occurrence in the Xinjiang area was first discovered in an apple orchard in Xinyuan County. Since then, this beetle had rapidly invaded into wild apple forests in Ili Valley of Tianshan Mountains, where it had killed thousands of wild apple trees. So far, chemical control has been the mainstay for managing this pest, and effective detection and monitoring tools are lacking. Insects can use various semiochemicals in host plant location and intersexual communication. Therefore, it is possible to develop semiochemical based management strategies for this pest. In addition, it has been difficult to determine the sexes for A. mali adults. In this study, morphological characteristics and the sensilla forboth sexes of this pest are described and analyzed. This will provide a basis for developing semiochemical based management stragies for this invasive pest. Our results are as follows:(1) In our study, the sex of A. mali adults can be determined based on newly identified morphological characters. For the lengths of body, thorax, femur of legs, the second segment of abdomen, and antenna, they are all longer in females than those in males. The width of abdomen in female is also bigger than that in male. In addition, tThe hair arrangement in prosternum of females is random, whereas it looks like a vortex and has a central point in males. The colour of prosternum, and 1st and 2nd segments of abdomen in males is green-like, and they are bronze-coloured in females. According to the abovementioned features, we can quickly identify the gender of Agrilus mali adults in the field and laboratory experiments.(2) The serrate-shaped antenna is located on the head between compound eyes. It has three segments: scape and pedicel, and flagellum that contains nine distinct flagellomeres. And their cuticular surface appears sculptured. The average antennal lengths of females were significantly longer than males. Fourteen subtypes of sensilla were found on antennae of male A. mali, and they could fall in five morphological classes: sensilla chaetica(Sc, 4 subtypes), sensilla trichoidea(Tr, 3 subtypes), sensilla basiconica(Ba, 4 subtypes), multiporous grooved sensilla(MPG), and B?hm bristles(BB, 2 subtypes). Thirteen subtypes of sensilla were found on antennae of females, female have no sensilla trichoidea type 3. In position, sensilla basiconica(Ba.1-4) are mainly located in the apical depressions of flagellomeres, and they account for over 64% of the total number of all types of sensilla in both sexes. Sensilla of Ba.2 are found to be the most numerous among the four subtypes of basiconic sensilla, and they contribute about 81% in males and 76% in females to the total number of basiconic pegs. In addition, MPG and sensilla trichoidea are also located the 2nd – 9th flagellomeres, which account for 2% and 9% respectively. Sensilla chaetica are the longest in length and located every segment, which accounted for about 20% of the total number of sensilla in both sexes. B?hm bristles are mainly locating in dense clusters on the wide sockets of the joints between the scape and the head of females and males. Sensilla chaetica and B?hm bristles have mechanical function. Sensilla trichoidea, basiconica and multiporous grooved could sense olfactory chemical information. In addition, multiporous grooved sensilla can also sense the temperature changes.(3) In addition to antennae, other parts of A. mali body also have unique types of sensilla, which include macrobristle, sensilla campaniformia and sensilla coeloconic. These sensilla of on the entire body of Agrilus mali are important in behaviors of feeding, seeking, mating and oviposition, for which further studies are needed. |
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