| The Bactrocera minax (Enderlein) (Diptera:Tephritidae), which is the most invasive and devastating pests of citrus, the citrus are harmed seriously and the development of citrus industry is affected seriously. Temperature and food are the main two environmental factors which usually restrict insect growth and reproduction activities. Once the two factors up to stress level, will the insects show abnormal behavior, such as the vitality reduced, lifetime shorten, development stagnated and fertility decline and a series of adverse situation. The occurrence and damage of B. minax is often affected by environmental factors (such as temperature and food), since the influence of these environmental factors on the growth and reproduction is not clear, and lack the mature prediction technique, result in harming again and again, and having a rising trend in partly citrus production areas. In this paper, the influence of environmental factors from environment temperature stress and food stress on the growth and reproduction of B. minax was studied. The super cooling point and freezing point of the mature larvae and overwintering pupa of B.minax (including diapause pupae and remove diapause pupae) were determinated, the tolerance ability and adaptation strategies of B.minax under low temperature stress were also discussed. We also studied the LT50, LT90 and the hatching rate of eggs under the short-term high temperature exposure of different gender and age of B.minax. Different feeding frequency were set to achieve the different feeding interval, and then we studied the influence of hunger stress on adult lifetime, mating and ovarian development and reproductive characteristic of B. minax to definite the growth and reproduction strategy of B. minax under hunger stress. By feeding different concentration (0%-100%) of honey solution to achieve the different degree of nutrient concentration stress. And then, study the influence of nutritional concentration stress on lifetime, development and reproductive of B. minax adults, and the feeding reaction of adults under the different nutritional concentration stress. According to the results, it is very important reference value for prediction and forecast of B.minax. Now the main study results were summarized as follows:1. The tolerant ability of mature larvae and overwintering pupa of B. minax to low temperature stressThe temperatures of SCP and FP of B. minax varied among different individuals, but the ranges of variation in line with the normal distribution. There were significant differences among different developmental status when the temperatures of SCP or FP were compared. The temperatures of SCP and FP at the post-diapause pupa were the lowest,-11.15 and -9.76℃, respectively, and then followed by the diapause pupa,-8.93 and -7.63℃, respectively. The temperatures of SCP and FP of mature larva were -7.09 and -3.43℃, respectively. The differences between the temperatures of FP and SCP at mature larval was the largest (3.24℃), that was significantly higher than those at diapause pupa (1.30℃) and post-diapause pupa (1.39℃). It indicated that there is no negative influence on B. minax pupa even though the late spring coldness.2. The thermotolerance of B. minax adults and eggsIn this study, the effects of brief exposure to high temperature on adult survival (at 35-45℃) and egg hatch (at 39-47℃) of B.minax were evaluated under laboratory conditions. When they were treated with 20,40 and 60 min at 35-45 ℃, the temperatures that caused 50% and 90% knockdown of adults were 39.3,39.0,38.6℃ and 40.3,40.5,40.4 ℃, respectively. The temperatures that caused 50% and 90% death of adults (LT50 and LT90) were 43.5,42.4,40.32℃ and 44.7,43.0,42.01℃ respectively. The thermotolerance of adults is negatively correlated with age, when 0, 10,20,30 and 40-day-old adults were treated with different temperatures respectively, the LT50 were 41.91,41.41,40.32,39.46, and 39.19 ℃, while the LT90 were 43.16, 42.77,42.01,41.37 and 40.72℃ respectively. The LT50 and LT90 of females were higher than that of males (except 10-day-old). The proportion of 20-day-old female adults after 1 h treated at 42℃ and 30 old-day female adults at 40℃ and 41℃ were 80%,64% and 72%, respectively, were all significantly higher than the control of 27℃ which was 50%, it means that the females were more thermotolerant. There were significantly effect on the egg hatch when they were exposed at short-term high temperature. When exposed of 1 h,2 h,3 h and 4 h at high temperature of 39℃, the hatching ratio of B.minax eggs were 20%,21.11%,47.78% and 42.22%, respectively, were all significantly lower than the control of 27℃ which was 83.33%. With exposure temperature rising, hatchability of eggs showed a decline trend follow with rise firstly in total, when they were exposed with 1h at 43℃, the hatchability of eggs was same with control. To 45℃ and 47℃, whenever exposure time, the hatchability of eggs dropped significantly lower than controls.3. The survival and reproductive strategy of B. minax under starvation stress(1)The lifetime of female adults under heavy starvation stress (feeding interval 4d) was 34.64d, was significantly shorter than the lifetime of female adults fed interval 1d (42.93d), the lifetime of male adults under slight and heavy starvation stress were 35.56d and 34.61d, respectively, there were no significantly difference with feeding interval 1d (40.26d). Compared with the adults fed interval Id, the second mortality peak of female adults under heavy starvation stress was 10d in advance, however, the second mortality peak of male adults under slight starvation stress was 40d in advance, the end time of female and male adults under slight and heavy starvation stress were 10d～20d in advance.(2)The mating times of adults paired 20 under slight starvation stress was 39.4, was significantly lower than that fed interval 1d (71.8), however, the mating times of adults under heavy starvation stress was 61.8, there were no significantly difference with that of feeding interval Id. The mating peak of adults under slight and heavy starvation stress had no significantly change, they were 27d after eclosion as well as that of feeding interval 1 d.(3)Under slight starvation stress, the oviposition peak of female adults was 34 days after their eclosion, and compared those which were fed interval Id (34d after eclosion), differences were not significant, while the total fecundity of adults paired 20 for their lifetime was 38.4 grains, which was distinctly lower than those fed interval 1d (167.8 grains). However, under heavy starvation stress, the oviposition peak (47 d after eclosion) of female adults was delayed 13 days compared those fed interval Id, and their fecundity (116.8 grains) was also remarkably decreased but significantly higher than that under slight starvation stress.(4)The second stage ovaries occupied 55% and third stage ovaries occupied 10% at 1 Od and 15d when starved at 5-day-old, were higher than the continuously nutrition supplement, however, they were all dead at 20d. It means that starvation at 5-day-old can promote the ovaries development at same degree, but their lifetime will shartly reduced. The progress of ovaries development of female adults starved at 10d、15d、 20d、25d and 30d were slower than the continuously nutrition supplement at the same time. In sum, it was disadvantage to ovaries development of B.minx under starvation stress.4、The influence of nutrient concentration stress on growth and reproduction of B. minax adults(1)Nutrient concentration stress significantly reduced the adults lifetime, the adults only survived 6.01 d when nutrition deleted completely to a concentration of 0%, was significantly shorter than the lifetime of adults fed with conventional concentration (5% and 10%), which were 20.39d and 18.43d respectively. The adults lifetime was 17.57d and 17.43d under sub-high concentration (20% and 40%) nutrient stress, were also significantly lower than the lifetime of adults fed with conventional concentration 5%. The adults lifetime (13.5d,13.35d and 10.225d respectively) under high concentrations nutrient stress (60%,80% and 100%) were also significantly lower than that fed with conventional concentration (5% and 10%). It means that adults must intake nutrient to survive normally, and the higher the concentration, the more obvious the role of stress, more significantly shortened lifetime.(2)The death progress of adults was aggravated and death peak in advance under nutrient concentration stress. The death peak of adults under nutrition absence completely was earlier 13-18d than that fed witn conventional concentrations (5% and 10%). The death peak of adults under sub-high concentration 20% was same with conventional concentration 5%, all of them were 20 d after eclosion. However, the death peak of adults under sub-high concentration 40% was not prominent. The mortality peak of adults under high concentrations nutrient stress were 11～17d ahead than that fed with conventional nutrient concentration (5% and 10%).(3)The mating and oviposition of adults were affected significantly under nutrient concentration stress. The mating of adults under sub-high concentration (20%) nutrient stress was observed only at the 16d,17d and 22d after eclosion. There was no mating behaviour occured when concentration of nutrition missing completely or sub-high concentration 40% and high concentrations stress, there was no mating of adults. And there was no spawning under the nutrition missing completely, sub-high and high concentration nutrient stress.(4)The nutrient concentration stress can lead to unnormal death of adults, sub-high and high concentrations stress lead to the mortality of adults eaten overload increase, while the mortality of adults starved increase when nutrient concentration missing completely. The mortality of adults eaten overload were 33%,49% and 44% respectively under sub-high concentration 40% and high concentration 60% and 80% stress, were significantly higher than that fed with the conventional concentration 5% and 10% which were both 16%. When nutrient concentration missing completely, the mortality of adults starved was up to 36%, was significantly higher than the conventional concentration 10% which was 13%.(5)The nutrient concentration stress affectted the feeding of adults significantly. When nutrition missed completely, the food consumption of female and male adults were 5.81mg and 4.25mg respectively, it was significantly lower than that fed with 10% concentration of nutrition which was 10.88mg and 10.67mg. The adults eaten more under the sub-high and high concentrations nutrition stress. When the nutritient concentration was up to 60%, the food intake of single female and single male achieved the highest, were 15.10 mg and 12.97 mg, and were significantly higher than that fed with conventional concentration(5%). High nutrition stress reduced the feeding effective, when the nutritient concentration reached 80% and 100%, the feeding effective of males and females (80%,3.59 mg/min and 1.76 mg/min; 100%:0.19 mg/min and 0.28 mg/min), were significantly lower than that fed with conventional concentration(5%:14.84 mg/min and 5.53 mg/min and 10%:9.92 mg/min and 7.28 mg/min). |
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