| Fruit flies are major and widespread destructive pests in agriculture worldwide with the larval stages being frugivorous on a wide range of fruit and vegetables. In China, Bactrocera cucurbitae (Coquillett), B. diaphora (Hendel), B. dorsalis (Hendel), B. minax (Enderlein), B. scutellata (Hendel), and B. tau (Walker) are commonly found in field. Among these six species, the oriental fruit fly, B. dorsalis is one of the most economically important fruit fly pests in tropical and subtropical regions. As an example, the annual investigation of fruit flies in China showed the presence of B. dorsalis in more than 10 provinces, and may expand to Northwest and Middle China as a consequence of the global climate warming.Fruit flies (Diptera:Tephritidae) are most important pests of fruits and vegetables. In this study, the typology, number, size, and distribution sensilla of female and male adults of six fruit fly species (Diptera:Tephritidae), B. cucurbitae, B. diaphora, B. dorsalis, B. minax, B. scutellata, and B. tau, were compared by scanning electron microscopy. Electrophysiological and behavioural responses of the oriental fruit fly, B. dorsalis to host-plant volatiles were examined by electroantennogram (EAG) and four-armed olfactometer. This research was supported by the National Basic Research Program of China (2009CB125903), Natural Science Foundation of Chongqing (CSTC, 2009BA1042) and the Specialized Research Fund for the Doctoral Program of Higher Education (2010018212002). The main results of the research are as follows:1 Sensillum ultrastructure of fruit flies1.1 Ultrastructure of sensilla on maxillary palpi of six Bactrocera fruit fliesThis study used scanning electron microscopy to analyze the external morphology, typology, size, and distribution of maxillary palpus sensilla of both female and male adults of 6 fruit fly species, B. cucurbitae, B. diaphora, B. dorsalis, B. minax, B. scutellata, and B. tau. The palpus is equipped with sensilla chaetica (SC), sensilla basiconica (SB), and microtrichia (MI). The distribution patterns of sensilla on the maxillary palpi of females and males of 6 fruit fly species were very similar. The abundance of sensilla differed significantly between species, and there were significant species×sex interactions;however only the distally distributed SC had significant differences between sexes. In addition, the possible functions of the sesillum types are discussed. Probable functions include the mechanoreception of sensilla chaetica and microtrichia, and olfaction of sensilla basiconica.1.2 Ultrastructure of sensilla on tarsi of six Bactrocera fruit fliesIn this study, the typology, size, and distribution pattern of tarsi sensilla of female and male adults of six fruit fly species, B. cucurbitae, B. diaphora, B. dorsalis, B. minax, B. scutellata, and B. tau, were analyzed by scanning electron microscopy techniques. The fruit flies legs consist of coax, trochanter, femur, tibia and tarsus. The tarsus had five segments with different type sensilla in pro-, meso-, and meta-thoracic legs. The tarsi are equipped with three types, sensilla trichoid (1,2,3) (ST1, ST2, ST3), sensilla chaetica and sensilla basiconic. The five segments of tarsi on female and male of the six fruit fly species were densely covered by parallel rows of these numerous small ST1. The ST2 was only located on the ventral of the first to forth tarsomere of the fruit flies. The ST3 was only present on the distal of the last tarsomere. The SC occurred on the tarsi of both sexes of six fruit flies. The SB were numerous occurred on the 1-4 tarsomeres, it was not found on the last tarsomere. In our study, no sexual difference in the length and diameter of trichoid sensilla were dectected (1,2, and 3). It suggested that that these sensilla expected that they are phasic in their response to mechanical stimuli. Among those six fruit flies, the chaetica sensilla may act as mechanoreceptor during the fruit flies move or stand to obtain the information. The SB may act as a chemoreceptor function suggests this type sensilla may help fruit flies in detecting the chemicals and/or odours.1.3 Ultrastructure of sensilla on ovipositors of six Bactrocera fruit fliesIn this study, the typology, number, size, and distribution pattern of ovipositors sensilla of female and male adults of six fruit fly species, B. cucurbitae, B. diaphora, B. dorsalis, B. minax, B. scutellata, and B. tau, were used by scanning electron microscopy echniques. Three types of sensilla are identified on the ovipositors:sensilla trichoid 4 (ST4), sensilla trichoid 5 (ST5) and sensilla campaniform. The ovipositor consists of three segments. The ventral third segment consists of two valves with numerous of campaniforma sensilla.The distribution pattern of sensilla on the ovipositor of females of six fruit fly species are very similar. The abundance of sensilla differed significantly between species. The ST1 may act as mechanosensitive, may support to females in finding suitable egg laying places since fruit flies lay eggs in fruit. The ST5 on the ovipositor might have tacile functions in controlling the position of the oviposited eggs. The sensilla campaniform may have a mechanoreceptorial function, it did not investigate other parts than the ovipositor for sensilla that might play a role in oviposition.2 Electrophysiological and behavioural responses of the oriental fruit fly, B. dorsalis to host-plant volatiles2.1 Electrophysiological responses of B. dorsalis to host plant volatilesThe electrophysiological responses of the oriental fruit fly, B. dorsalis to 16 plant volatile substances were determined through EAG technique. The result showed that EAG activity responses of B. dorsalis had significant differences among males, female mature and female virgin and diverse plant volatile substances. Hexanol, 1-Octen-3-ol, trans-2-Hexenal and Limonene at dose 10μg/μL elicited significantly greater EAG responses in male of B. dorsalis. Significant differences were also recorded in the EAG responses of males to the same plant volatile substances of different doses (100μg/μL, 10μg/μL,1μg/μL,0.1μg/μL), all plant volatile at 100μg/μL elicited greater EAG response than the other three doses (10μg/μL,1μg/μL,0.1μg/μL).Hexanol elicited the highest EAG response in female mature of B. dorsalis.1-Octen-3-ol, ethyl acetate, acetic acid and methyl eugenol also elicited higher responses to female mature of B. dorsalis.Similarly, EAG responses of female mature of B. dorsalis to high dose(100μg/μL) was greater than EAG response of female matures to low doses (10μg/μL,1μg/μL,0.1μg/μL). Significant differences were also recorded in the EAG responses of female virgin of B. dorsalis to hexanol, hexanal, citral and acetic acid. Similarity, high dose (100μg/μL) elicited EAG response of female virgin of B. dorsalis greater than the other doses (10μg/μL,1μg/μL,0.1μg/μL).2.2 Behavioural responses of B. dorsalis to host plant volatilesIn this study, a four-arm olfactometer was used to test the responses of male, female mature and female virgin of B. dorsalis to 13 plant volatile substance.In all olfactometry bioassays, treatment odors were compared against three controls and centre region. Results showed that hexanol, 1-octen-3-ol, trans-2-hexenal, methyl eugenol, ethyl acetate, acetic acid attractive to male, female mature and female virgin of B. dorsalis more times and number entries than the other 7 plant volatiles.Significant defferences were detected among 13 plant volatiles in B.dorsalis males. B. dorsalis males entered more entries of hexanol and ethyl acetate and spent more time in methyl eugenol and ethyl acetate (5.52 min; 6.34 min) than the other substances. Meanwhile, male of B. dorsalis entered the selection regions of treatment odors more frequently than those of controls. Male of B. dorsalis spent significantly more time in treatment area compared to control. Similarity, female mature B. dorsalis spent most time in the treatment area of hexanol (5.14 min) and ethyl acetate (5.14 min) of all 13 plant volatiles. Female mature B. dorsalis stayed significant more time in treatment area than in control area. Significantly differences were detected among total times spent in each olfactometer arm of treatment region and control region. B. dorsalis female virgin were significantly induced by 1-octen-3-ol, ethyl acetate, hexanol and acetic acid, and spent time in ethyl acetate region was 5.62 min. As well as B. dorsalis males and female matures, B. dorsalis female virgin entered the selection regions of treatment odors more frequently than those of controls. Meanwhile, female virgin of B. dorsalis spent significantly more time in treatment odor fields compared to control odor fields. |
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