| Bradysia odoriphaga Yang et Zhang is one of the most important insect pests on edible alliaceae and its most favor host plant is Chinese leek. The local name of its larvae is root maggot. It is difficult to control the pest because of its life behavior and limited number of insecticides that can be used safely on crops. Therefore, great damages have been caused to leek production. What is more serious that many farmers turn to apply insecticides with high toxicities to mammals, which leads to high level of insecticide residue in commercial leek product. And few consumers would like to risk life to buy leek product up to now. B. odoriphaga is a insect specifically to China. Before 1990, simple biological characteristics and occurrence law were investigated. But no systematically data were obtained, and usually there was significant difference between different results. After 1990, the research work on the insect was focused on selecting effective insecticides and control methods, but still no effective control strategy was formed. In general we know little about the insect, which is one of the main reasons of difficult control, and there is much research work need to be done.To keep a feasible humidity is the most crucial factor to rear B. odoriphaga in laboratory successfully. In present study keeping humidity by moistened filter paper or 2.5% agar in Petri dish can both obtain large number of experimental insects. Combing two methods can save labor and decrease the possibility of infection of bacteria obviously, and at the same time increase the survival rate of the larvae.The biological characteristics of B. odoriphaga at 15℃, 20℃, 25℃ and 30℃ were investigated. Results showed that the developmental period of different stages was shortened with the increased temperature. The longest development period of the whole generation was found at 15℃, which was 72.36 days. And the shortest was at 30℃, which was 21.63 days. Others at 20℃ and 25℃ were 27.24 days and 23.85 days respectively. The developmental zero of egg, larva, pupa, adult and egg-pupa of B. odoriphaga was 5.85 ℃, 8.27℃, 3.34℃ and 7.8℃. And the effective accumulative temperature was 77.68, 267.22, 75.72 and 48.2 day temperature respectively. The lifespan of B. odoriphaga adult was shortened with the increased temperature too. The longevity of male adult at 15℃ was 7.73 days, however it was only 4.70 days at. The lifespan of female was 11.65 days at 20℃, and shortest was 4.13 days at 30℃. As a whole, the lifespan of female was longer than that of male adult expect the 30℃ condition. The maximum number of eggs laid by per female was 159.86 at 20℃, the least was 114.73 at 30℃. Both over high and over low temperature were not helpful to oviposition. The life tables of B. odoriphaga at 15℃, 20℃, 25℃ and30℃ were established. Results indicated that temperature had great effect on the survival rate of the first instar larvae. The most favorable range of development temperature was 20 ℃ to 25℃, during which there was the highest population trend index and higher innate capacity of natural increase. The average survival rate was 60% at the four different temperatures.A continuous observation of 11 piles of egg developing from hatching to eclosion was conducted. Results showed that the rate of egg file developing into entire female was 36.3%, the male was 45.4%, and some male and some female was 18.2%. The sexual ratio of five continuous generations was also observed. The ratio of female to male were 1.36, 1.31, 0.84 and 1.39 respectively. These results indicated that the sexual ratio disorder in part of population had no great effect on the whole population.The supercooling points and ice points of 3rd instar larvae of B. odoriphaga were -14.05℃ and -11.07℃, and the fourth instar larvae were -13.98℃ and -9.94℃. There was no significant difference between 3rd and 4th instar larvae. But the supercooling point and ice point of pupa is higher than 3rd and 4th instar larvae, which were -11.6℃ and -8.08 ℃ respectively. The... |
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