Studies On Biological Characteristics And The Impact Of Environmental Factors On Strepsicrates Coriariae Oku

Strepsicrates coriariae Oku (Lepidoptera:Tortricidae) has been one of the important moths of young shoots of eucalyptus in southern coastal provinces of China, since 1970s. To investigate the occurrence and control of main fruits and vegetables of Fujian from Taiwan in 2009, we found that S. coriariae severely damage Psidium guajava L’s shoot and leaves. In order to effectively control the spread of S. coriariae and reduce its demage, we carried out a series of studies on the biological, ecological and physiological characteristics of S. coriariae to understand and grasp the occurrence characteristics, providing theory basis for integrated pest management. The main results are as follows:1. Biological characteristics and population dynamics of S. coriariae in guava orchardsS. coriariae had 7 to 9 generations per year in Fuzhou, and generation overlapped significantly, it can overwinter by larvae and pupae. Most of the larvae have five instars, some have 4 or 6 instars. The last instar larvae had three black dorsal stripes while other instars had nothing or only a little. The guava’s main fruiting season is from May to October every year, so May to October is the damage period of S. coriariae. The duration of damage peak was from July to September and the damage rate of guava sprout could reach more than 60% during this time, or even caused crops production of reduce and significant economic losses of growers. The silk of larvae spined up disstretch the leaves which could favor its feeding or hide on fruits to feed on for scar formation which reduce the quality of fruits and affect its economic value.2. Sex identification of S. coriariaeAccording to the previous method, we analysed the sex characteristic of S. coriariae’s in detail. By the long-term isolation rearing and the observation of anatomy under microscope, we summarized some methods to identify the S. coriariae’s sex. Whether the fifth abdominal segment of larvae with male reproductive buds, pupa’s seventh or eighth abdominal ganglia intersegmental fold is apparent, adult’s wing with a raised scales is the characteristic of stable feature to quickly distinguish between male and female of S. coriariae. The experiment is tend to quick and accurate identification of the male and female in the field such as gardens and orchards to find out the sex ratio, and it has an important influence on its biological characteristics, the population dynamics and forecast of S. coriariae.3. The effects of Temperature on S. coriariaeLaboratory studies were conducted to assess the effect of temperature on the development of S. coriariae at 16℃,20℃,24℃,28℃ and 32℃ under a photoperiod of 14 h:10 h (L:D). The results showed that the developmental duration shorten while the temperature increased from 16℃ to 32℃ and the optimum temperature zone was between 24℃ and 32℃. The developmental threshold temperatures for egg,1st instar larva,2nd instar larva,3rd instar larva,4th instar larva,5th instar larva, pupae, and the whole generation were 9.15℃,11.46℃,7.44℃,8.24℃,6.37℃,7.68℃, 10.32℃ and 8.58℃, respectively.And the corresponding effective accumulated temperatures were 67.10,34.56,42.78,37.84,50.60,113.25,127.40,506.67 degree-days, respectively. According to the effective accumulative temperature law, we theoretically predicated that there are 8.45 generations of this pest in Fuzhou which was close to the actual 7 to 9 generations in 2012.S. coriariae isn’t perennial of insects, without over-wintering and over-summering in Fuzhou and the number generations of theory are in according with those of the actual situation, so we can use the developmental threshold temperature and effective accumulated temperature to predict the beginning and peak period of S. coriariaeand to provide theory evidence accurately, for timely spraying control.4. The effects of photoperiod on S. coriariaeStudies were conducted to assess the effect of photoperiod on the development of S. coriariae at 6 photoperiods (L:D=22:2,18:6,14:10,10:14,6:18,2:22) under 25℃. The results showed that the adaptability to photoperiod between different instars was significantly different and the final instar larvae and pupae presented stronger to photoperiod than the other instars, which indicated that S. coriariae could adjust their developmental period to adapt the changing light photoperiod. There was no difference between the developmental duration of eggs, larvae and pupae, preoviposition period, oviposition period, lifetime fecundity and longevity under the photoperiod of L:D=14:10 and L:D=10:14, no significant differences (p> 0.01 and p> 0.05) during which S. coriariae had the shortest developmental duration, maximum fecundity and the longest oviposition period, so this photoperiods were the most suitable for the pervasion and proliferation of S. coriariae. This test was designed to study the effects of temperature and photoperiod on the population growth of S. coriariae for knowing more about how the environmental conditions impact on their growth and development. The results indicated it’s more conducive to S. coriariae’s development and population growth during 24～32℃ and 10 -14h light, which was also in accordance with the environmental conditions of S. coriariae’s high-occurrence season (from June to September).5. Effects of host plants on S. coriariaeTo explore the effect of host plants on the developmental duration of S. coriariae larvae by feeding on guava leaf growing during autumn and winter of 2012 and spring and summer of 2013. And the first generation female moths of net-room in 2013, which fed on guava, Eucalyptus urophylla×E.grandis or Eucalyptus grandis x E.urophylla, were dissected and the diversity in their ovariole number was investigated. (1) Excluding the effects of temperature, the development duration of larvae in spring or summer is shorter than that in autumn and winter. (2) The ovary development of larvae on guava and Eucalyptus urophylla×E.grandis has no difference, but the ovary development of Eucalyptus grandis×E. urophylla differed significantly. In summary, the indoor ecology study should grasp the time and select the suitable host to avoid the error caused by quarters cross or physiological differences.6. Toxicity test of 12 insecticides against S. coriariaeToxicity of the 12 insecticides to the 3rd instar larvae of leaf roller(Strepsicrates coriariae Oku) was determined by leaf dipping method. The results showed that the most sensitive insecticides was abamectin and its LC50 value was 0.04 mg.L-1, while metaflumizone had the lowest toxicity to S. coriariae and its LC50 value was 469.31 mg.L-1. The order of toxicity to S. coriariae was abamectin> virtako> chlorpyrifos> spinetoram> alphacypermethrin> chlorantraniliprole> indoxacarb> imidacloprid> flubendiamide> bisultap> chlorfenapyr> metaflumizone. Abamectin was the most susceptible to S. coriariae with 11732.68 of relative toxicity index, then followed by virtako, chlorpyrifos, spinetoram, alphacypermethrin, chlorantraniliprole, indoxacarb with relative toxicity indexes of 1130.86,717.60、619.96,607.12,373.36 and 272.22, respectively. The other insecticides were not susceptible to S. coriariae with< 100 of relative toxicity indexes. Especially, chlorfenapyr was the least susceptible with only 1.16 of relative toxicity index. The results provided basis for reasonably insecticides choice and field control of leaf roller in guava orchards.7. Reproductive system of S. coriariaeThe structure and developmental process of the ovaries of S. coriariae were observed by dissecting females at different stages of development maintained in an incubator chamber at 25 degrees. The results showed that the female reproductive system consisted of two ovaries and each of them included four polytrophic ovarioles. Ovarian development of the female reproductive system was classified into four stages, including yolk sedimentary stage, egg-matured stage, egg peak stage, late egg-laying stage. The experimental results showed that the proportion of egg peak stage and fecundity changes had a significant correlation. According to the change of female fecundity, the total amount of eggs are 300 or more per female, we could speculated that S. coriariae females start to oviposit in 2 or 3 days after emergence, and the period of oviposition was up to 4 days. The ratio of three levels of ovary can reflect the change of average fecundity, so it is possible to predict the peak oviparous period of the next generation by monitoring the female reproductive system of the current generation.