| Bioassays of 6 typical insect growth regulators (IGRs) for eggs, larvae and adults of Delia antiqua (Meigen) (Diptera: Anthomyiidae) were examined in the laboratory. The larval growth and development, adult fecundity and subsequent effect were observed. From the facts of larval poisoning procession, poisoning symptom, structures of integument, biochemical and physiological condition, we explored the mechanism of IGRs' function. The main results are as follows: 1. Among 6 IGRs provided, hexaflumuron's toxicity to 1st, 2nd and 3rd instars of D. antiqua was the highest, followed by cyromazine, lufenuron and chlorfluazuron, and then by diflubenzuron. Tebufenozide had no effects. Toxicity of hexaflumuron(0.6622mg/L) and lufenuron (0.9611mg/L) to 3rd instars was higher than that of phoxim(1.2569mg/L). 2. The results of bioassays showed lufenuron and chlorfluzuron could inhibit eggs hatchability, but the effects were lower than those of phoxim and Chlorpyrifos. Cyomazine and hexaflumuron's effects on 1st, 2nd and 3rd instars treated in the laboratory were the highest, followed by lufenuron, diflubenzuron and chlorfluazuron, and tebufenozide had no effect. By diluting cyromazine, chlorfluazuron, hexaflumuron and tebufenozide with milk to 2000-fold solution, which were used to feed adults for 15d, we found mortalities of adults were all lower than 18.2% .3. The inhibiting effects of 5 IGRs in LC30-40 dosage on larval growth and adults fecundity were remarkable. The function of cyomazine and hexaflumuron was more significant than that of other 3 IGRs. The results of 1st instars treated with cyomazine and hexaflumuron, both insecticides prolonged the larval development periods, caused larval continually dead, reduced eggs laid, decreased adult longevity and prolonged preoviposition, but they didn't affected adult emergence rates. When larvae were treated in 3rd instar, cyromazine and hexaflumuron didn't kill larvae, but led to pupal deformity, reduced pupal weight, eggs laid and adult longevity and also prolonged preovipositon. However, neither cyromazine nor hexaflumuron affected eggs' hatchability when larvae treated in 1st or 3rd instar.4. Although they couldn't directly lead adult to dead, cyomazine and hexaflumuron severely affected adult fecundity. The eggs laid per female adult were 163.8 and 259.8, respectively, versus 352.8 of the controls. Mortality of 1st instars was very high, no less than 95%. 5. Significant mortality due to hexaflumuron treatment was observed after 1stinstars molted, while the same effect with cyromazine treatment was observed after larvae molted. Under the microscope, the empty between epidermis and endocuticle was detected when 1st instars were treated with hexaflumuron. The structures of endocutilce and exocuticle were affected with cyromazine treatment. The endocuticle was folded and the exocuticle was discontinuous. The toxicological mechanism of cyomazine and hexaflumuron was different.6. The biochemical test showed the activity of CarE was higher than that of the controls, and activity of AChE was unchanged when the 3rd instars were treated in different time. The protein content of larval body was in the same level 24hr after treated.7. When 1st, 2nd and 3rd instars were treated with 3000-fold solutions in the pot test, the results demonstrated the control effect of cyomazine (91.1-96.4%) was better than hexaflumuron (85.6-86.1%), but both of them were insignificantly lower than that of phoxim. Another test showed cyromazine in soil had effects on 1st and 2nd instar larvae more than 15d, and on 3rd instars more than 10d, which was similar to those of phoxim. |
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