Studies On Biology, Ecology And Resistance To Insecticides Of Crocidolomia Pavonana

Crocidolomia pavonana (Fabricius), a major pest of cruciferous crops in some regions of Asia, was found firstly and had seriously damaged the vegetable crops in recent years in Nanning, Guangxi Province. The biology, ecology and resistance of C. pavonana (Fabricius) had been studied. The results were as follows:C. pavonana occurred nine generations annually in field in Nanning, and the generations were seriously overlapped. The main hosts of the moth were the crops of Cruciferae, such as: Sea cabbage, cabbage, leaf mustard, radish and rape. The peaks of population density of the moth occurred from April to June and September to November. The larvae had four instars and damaged the leaf, tender stem and flower of its hosts, and jumped to the soil to pupate. It overwintered by pupae from December to March. It had thirteen generations a year in laboratory in Nanning, and spent 18～39.5 days to complete one generation. The developmental period of egg , larvae and pupae were 2.5～6.5 days,8.0～13.0 days and 6.0～17.0 days, respectively. In suitable condition, the female laid 149 eggs per head, and the life span of female averaged 11.7 days.The host preference of the larvae of C. pavonana for the seven crops of cruciferous vand the effect of hosts on the development of the larvae were tested. The results indicated that the larvae prefered to feed on the cabbage mustard, compared to the other crops tested. The amount of intake of food by the larvae on the cabbage mustard was 72.91 mg dried substance per head, which was obviously higher than that of on the radish, which was 15.90 mg dried substance per head only. The difference of the developmental period and survival rate of the larvae were great when the larvae were fed with different host plants. The duration of the larvae fed with the cabbage and the radish became longer, which were 18.7 days and 18.53 days, respectively, when the duration of the larvae fed with the sea cabbage and the cauliflower were shorter, which were 10.20 days and 11.21 days, respectively. The survival rates of larvae fed with the cauliflower and the leaf mustard were more than 95%, while that of the larvae fed with the radish was 57.14% only. The above results indicated that sea cabbage, cabbage mustard, leaf mustard, cauliflower, cabbage, rape and radish of cruciferous vegetables all were the host plants of C. pavonana. The moth had a preference for the cabbage mustard and the leaf mustard, and the radish was not a suitable host plant for C. pavonana.The influence of temperature on the growth of C. pavonana were investigated. The suitable temperature regions of the growth of C. pavonana were from 25℃to 30℃. The moth only spent 16.86 days to complete one generation at 35℃, while it spent 90.99 days to complete one generation at 15℃. It had higher survival rates at 25℃and at 30℃, and had a lowest survival rate (26.1% ) at 35℃. The development zero of egg , 1st to 4th instar larvae, papue, and the whole generation of C. pavonana were estimated to be 8.57℃, 8.25℃, 6.72℃, 6.63℃, 5.89℃, 14.39℃and 11.18℃, respectively, and the effective accumulative temperatures for completing one generation was 403.73 d昢. Based on the results, it was calculated that the moth could develop about 9.5 generations annually in Nanning, which was consisitent with the result of the experiment in field.The results of the investigation in field showed that Euborellia pallipes (Shlirak) and Episyrphus balteatus (DeGeer) were main predatory enemies against the larvae of C. pavonana and no parasitoid of C. pavonana had been found yet. The functional response of E. pallipes against fourth instar larvae of C. pavonana at different densities suggested that E. pallipes preyed most greatly 17.85 heads fourth instar larvae of C. pavonana per day.The sensitivity of 3rd instar larvae of C. pavonana in the lab population to commonly used insecticides on the vegetable were determined with topical application method, and the relatively sensitive toxicity baseline of 10 pesticides on the larvae of C. pavonana were established. The results showed that the susceptible order was abamectin>lambda-cyhalothrin>fipronil>chlorpyrifos>chlorfenapyr>hexaflumurom> α-cypermethrin>methomyl>dipterex>cypermethrin. The sensitivity of C. pavonana to abamectin was the highest, and its LD₅₀ value was 0.00237μg/head, while that of dipterex was the lowest, and its LD₅₀ value was 0. 0.2727μg/head.Continuously selected with chlorpyrifos for 5 generations, the sensitivity of C. pavonana in the lab strain descended prominently. The LD₅₀ value(0.082μg/head) of F₅ generation after selection increased to 1.7-fold as compared with the LD₅₀ value(0.048μg/head) of F₀ generation. Based on the method described by Tabashnik (1992), the realized heritability (h²) of resistance to chlorpyrifos in C. pavonana was estimated to be 0.5708. It was predicted that the strain would require to spend 9.99～4.52 generations to obtain a 10-fold increase in resisitance to chlorpyrifos under selective pressure of 50%～90% mortality for each selective generation. The results of the determination of enzyme activity indicated that there were great difference in the activities of CarbE, GSTs and MFO between the resistant populations that were selected by chlorpyrifo and that of the lab populations, which suggested that the resistance of C. pavonana to chlorpyrifos had closely relationship with the three kinds of enzymes. These results will provide some references for the management of pesticide resistance of C. pavonana in field.