| The fruit fly Bactrocera tau Walker, belonging to the order Diptera and the family Tephritidae, mainly infests Cucumis L., Cucurbita L., Luffa L., Benincasa Savi, Momordica L. and other fruits and vegetables. It has taken place in tropic and subtropic regions such as China, Japan, Thailand, Malaysia, Laos, Philippines, Cambodia, India, Bhutan, Indonesia, Sri Lanka and has caused enormous economic losses to fruit and vegetable growers. In China, the fruit fly caused Siraitia grosvenorii Swingle damage up to 21-34% in Guangxi province in 1990 and was injurious to various types of vegetables in Chongqing district in 2004. Due to its economic importance, the study on biological and biochemical characters of this fruit fly was very necessary in the course of the production of fruit and vegetable crops. Based on the research status, the study on the population biological and biochemical characters, especially the physiological mechanisms of the fruit fly adaptable to diets and environmental temperature was carried out systematically. This study was supported by the Specialized Research Fund for the Doctoral Program of Higher Education (20050625005) and the Basic Research Foundation of Chongqing Science Committee (7468), and lasted almost 3 years. The main results are summarized as follows.1 The species richness and geographical distribution of fruit flies in ChongqingBy the Regional Fruit Fly Project in 2005-2006, systematic trapping using methyl eugenol, cue-lure and hydrolytic protein had been conducted in almost 30 regions of Chongqing. The total 174879 fruit fly samples trapped had confirmed the presence of Bactrocera tau Walker, B. diaphora Hendel, B. scutellata Hendel, B. caudate Fabricius, B. minax Enderlein, B. cucurbitae Coquillett, B. dorsalis Hendel and Dacus trimacula. Among them, B. cucurbitae, B. dorsalis and Dacus trimacula was firstly found in Chongqing district.Species relative abundance of fruit flies in Chongqing region was analyzed by dominance indexes. The dominance indexes of these fruit flies varied greatly among the 8 kinds of species. In 2005, the dominance indexes of B. tau, B. diaphora, B. scutellata, B. caudate, B. minax, B. cucurbitae and B. dorsalis were 0.8225, 0.1333, 0.0376, 0.0055, 0.0009, 0.0001 and 0.0001, respectively. In 2006, they were 0.7651, 0.0889, 0.1304, 0.0003, 0.0028, 0.0104, 0.0010 and 0.0011 (Dacus trimacula), respectively. The result indicated that B. tau was the dominant population in Chongqing region, B. diaphora and B. scutellata were the second great population, and the others were relatively low in quantities.According to the identification result of samples collected from different regions of Chongqing, they showed that B. tau, B. diaphora and B. scutellata widely distributed in Chongqing district, but B. minax, B. caudate and D. trimacula were found just in several locations. For B. dorsalis, 9 individuals were captured and distributed in Jiangbei, Yongchuan, Xiushan, Dianjiang and Fuling in 2005, and 95 individuals were captured and distributed in 16 regions including Jiangbei, Jiulongpo, Beibei, and so on in 2006. It showed that the distribution range obviously expanded in 2006. For B. cucurbitae, 10 individuals were trapped in 2005 and 956 individuals were trapped in 2006, and it indicated that the quantity captured in 2006 was significantly higher than that in 2005.2 The damage character and risk analysis of B. tau populationBy the field investigation and the previous study, we comprehensively evaluated the damage character and risk of B. tau. The result showed that B. tau mainly infected cucumber, pumpkin, towel gourd, white gourd, balsam pear and other fruits and vegetables in Chongqing district. Host surveys for this fruit fly in field had confirmed that the damage rate was highest on pumpkin and towel gourd, then on cucumber, and lowest on balsam pear among the five kinds of host fruits above-mentioned. Based on the system and indices of pest risk analysis, we estimated the risk of this fruit fly, and found that the index value of pest risk analysis (R) attained to 1.96. From the result, it could be inferred that this fruit fly was dangerous to some fruits and vegetables, and had posed a threat to other regions in China.3 The population character of B. tau and its relation with environmental humidityB. tau had 3-5 generations a year and the generations overlapped in Chongqing district. It was divided into 3 instars in larval stages, and overwintered as pupae in loose soils. Generally, adults mated for several times in the whole life, and the female laid its eggs in clutches under the skin of fruits. The larva or maggot fed on the flesh of fruits. In the process, bacteria were introduced into the fruit causing the fruit to break down or rot. More than 70% mature larvae pupated in the soil with 0-5cm depth, and the survival rate of pupae was higher than 88%. There were 3.74% individuals digging into the soil with 10-25cm depth, and the survival rate was lower than 65%. Only 3.33% individuals could survive in the soil depth over 25cm. The adult could emerge at every time of a day, but mostly aggregated on the time 6: 00-10: 00.The taxis response and selective propensity of B. tau to six types of fruits cucumber, pumpkin, towel gourd, white gourd, balsam pear and orange were evaluated under indoor experimental conditions. The result demonstrated that most of the adults would obviously prefer to aggregate on cucumber, pumpkin and towel gourd to gain nutrition or lay eggs. Among them, 23.68%, 19.94% and 21.18% of individuals gathered to cucumber, pumpkin and towel gourd, and 21.57%, 18.93% and 22.74% of eggs were lay on the same three host fruits, respectively. It was suitable, adopting linear regress equation, to describe the relationship between the mean quantities and the mean oviposition quantities. As adults, most larvae also aggregated on cucumber (23.33%), pumpkin (31.44%) and towel gourd (21.67%), but little individuals aggregated on orange (2.22%). In addition, the taxis response of the fruit fly to damaged and undamaged fruits was also different in the six kinds of host fruits, and＞50% of individuals would gather to the damaged fruits. From these results, it could seen that the fruit fly preferred to aggregate on cucumber, pumpkin, towel gourd and damaged fruits, but little on orange to gain nutrition or lay eggs.The effect of soil relative water content (SRWC) and air relative humidity (RH) on the pupal development and survival and the water loss dynamics of B. tau were evaluated under indoor experimental conditions. The pupating selectivity of mature larvae, the pupal duration and eclosion rate varied significantly in the soils with SRWC 0%, 20%, 40%, 60%, 80% and 100%. Most of the mature larvae aggregated on the soils with SRWC 20-60% although they could become pupae in the soils with different water content. When SRWC attained to 100%, all of the pupae failed to survive; SRWC 40% and 60% were most suitable for the pupal development, with the shortest pupal duration (7.54d and 7.65 d) and the highest eclosion rate (83.58% and 93.3%). In the 4 air RHs of 0%, 52%, 76% and 100%, the pupal water loss rates increased with the increase of the treatment time, and reached up to 63.521% for RH 0%, 45.42% for RH 52%, 34.23% for RH 76% and 10.99% for RH 100% at the last day before eclosion. It was suitable, adopting the quadratic equations, to describe the relationship between the water loss rate of pupae accumulated by day and pupal age in day. The pupal duration and eclosion rate were also significantly different in the 4 air RHs. The shortest duration (8.07d) and the highest survival rate (90.55%) of pupae were attained in the air RH 100%, and little individuals could survive in the air RH 0%. The results implied that high soil water content and low air humidity were unfit for the development and survival of B. tau pupae.4 The influence of diets on the growth and enzyme characterization of B. tauThe effect of different diets including cucumber, pumpkin, towel gourd, balsam pear, orange and artificial diet on the growth and fecundity of B. tau were evaluated at 28±0.5℃, RH 70±5% and photoperiod of 14:10 hours (L: D). The result demonstrated that the developmental duration and survival rate of larvae and the reproduction rate of adults differed significantly among the 6 kinds of diets. When the larva were reared on the above diets, the larval durations were 4.58d, 5.08d, 4.50d, 6.15d, 5.38d, 5.72d, the survival rates were 86.83%, 83.39%, 81.19%, 51.17%, 45.67%, 30.33%, and the total reproduction quantities per female were 99.56, 84.67, 85.91, 33.97 and 8.24, respectively. The result suggested that the larval durations were shorter, the survival rates were higher and the reproduction quantities per female were also higher on cucumber, pumpkin and towel gourd. According to the life-table parameters and the population trend indexes, it could be concluded that cucumber, pumpkin and towel gourd were the most suitable diets for the development and fecundity of this fruit fly, but contrary for orange and artificial diet.Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) are considered to be an important physiological and biochemical mechanism of organisms against adverse environmental factors. The soluble protein contents and those enzyme activities in B. tau fed on cucumber, pumpkin, towel gourd, white gourd and balsam pear were determined by biochemical methods. The result indicated that the protein contents and those detoxification enzyme activities varied significantly when the fruit fly were reared on different diets—cucumber, pumpkin, towel gourd, white gourd and balsam pear. Among the 5 kinds of diets, the protein contents in this fruit fly were highest on balsam pear while lowest on cucumber and white gourd. The SOD, POD and CAT activities were highest on balsam pear, then white gourd, but lowest on cucumber and pumpkin, and those enzyme activities also varied greatly in different developmental stages of this fruit fly. The SOD activity was highest at the larval stage, and lowest at the adult stage; the POD and CAT activities were highest at the adult stage, but lowest at pupal stage. Based on the above study, it indicated that the antioxidant activity in B. tau was lower when the fruit fly was reared on suitable diets, than that on unsuitable diets.This study was conducted to determine whether the activity of detoxification enzymes, such as carboxylesterase (CarE), acid phosphatase (ACP), alkaline phosphatase (ALP), cytochrome P450-dependent O-demethylase and glutathione S-transferase (GST) in Bactrocera tau (Walker), respond to different diets and developmental stages of this fruit fly. Two-way ANOVA showed that protein contents and these detoxification enzyme activities varied significantly when the fruit fly were reared on different diets cucumber, pumpkin, towel gourd, white gourd and balsam pear. Among the five kinds of diets, protein contents in the fruit fly were highest on balsam pear while lowest on cucumber and white gourd. The CarE activity was highest on cucumber and pumpkin, cytochrome P450-dependent O-demethylase and GST activities were highest on balsam pear, but ACP and ALP activities were lowest on cucumber and pumpkin, respectively. In addition, these detoxification enzyme activities were also significantly different in the larval, pupal and adult stages of the fruit fly. Adults had the highest CarE activity, and larvae had the highest ALP, cytochrome P450-dependent O-demethylase and GST activities, but the lowest ACP activity. Generally, these detoxification enzyme activities in the pupal stage were lower than those in the larval and adult stages except for ACP. The result indicated that these detoxification enzyme activities of B. tau were closely related to host plant species and developmental stages of this fruit fly.Polyphenoloxidase (PPO), a group of copper proteins thatare widely distributed from bacteria to mammals, catalyzes the oxidation of hydroxyphenols to their quinone derivatives, which then spontaneously polymerize. The kinetic properties of PPO from B. tau different stages were compared and determined by a series of chemical methods. The result showed that PPO activity differed significantly at different stages in this insect. The PPO activity of the 3rd instar was highest and that of pupae was lowest among the 1st instar, the 2nd instar, the 3rd instar, pupae and adults. The order of the enzyme activity was the 3 instar＞adults＞the 2nd instar＞the 1st instar＞pupae. The optimum pH was 7.0 and the best temperature was 34-37℃for the tested PPO. The kinetic parameter for the oxidation of catechol by PPO from the different stages was determined and compared, and it showed that the affinity of PPO to the substrates catechol was higher, but the catalytic activity was lower for the 2nd instar. At the same time, for the substrates L-DOPA, the Km for adults and Vmax for the 3rd instar of PPO were highest, it showed that the affinity of PPO for adults was lower, and the catalytic activity for the 3rd instar was higher than the other stages. From the above conclusion, it could be inferred that the property of PPO activities is closely associated with the developmental stages of B. tau.5 The influence of temperature on the growth and energy resources of B. tauThe growth and fecundity of B. tau fed on pumpkin were investigated at 6 constant temperatures 19℃, 22℃, 25℃, 28℃, 31℃and 34℃in a series of indoor trials. ANOVA showed that temperature affected significantly the developmental duration and reproduction capacity. The developmental duration of larvae varied from 6.31d at 28℃to 10.09d at 19℃, and the survival rate varied from 27.03% at 34℃to 74.76% at 28℃. The female adult at 19℃and 22℃had significantly greater longevity (96.29d and 94.00d) than those at the other temperature, and had the greatest reproduction capacity (105.91 eggs per female) at 28℃. Accordingly, the intrinsic rate of increase (rm) and the population trend index were highest (0.0572 and 17.28, respectively) for this fruit fly at 28℃. The results implied that the temperature of 28℃were the most suitable for the population development and fecundity.The longevity and energy sources including polysaccharides, triacylglycerol and soluble protein of B. tau submitted to heat shocks (42℃) of various durations (5,15, 30 or 60 min daily) for 10d or 15d were determined systematically by ecological and biochemical methods. A slight longevity increase was observed in 15min daily for 10d and in 5min daily for 15d, but longer shocks had negative effects. Fruit flies submitted to the procedure providing a longevity increase did not show a higher polysaccharide and protein contents than those in the other treatment durations. However, the highest polysaccharide and protein contents were observed in the control flies. Except for the control flies, the accumulation of triacylglycerol of this fruit fly increased responding to the treated durations. The above results suggested that under the heat shocks conditions, polysaccharides and soluble protein were the main energy sources, while the utilization of triacylglycerol decreased.Generally, the study on the bio-ecological characteristics, and the influence of diets and heat shock on the physiological and biochemical properties of B. tau has clearly elucidated the occurrence regulation, formative mechanism and biochemical mechanism of this fruit fly suitable to diets and temperature. The result will provide necessary information for IPM program, and enrich the whole theoretical system of fruit flies.
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