Adaptability Of Plutella Xylostella Of Field-collected Strain To The Different Host Plants With The Stress From Different Type Of Insecticides

The diamondback moth (DBM), Plutella xylostella (L.), is one of the most destructiveinsect pests of cruciferous crops and requires globally US＄1.0 billion in estimated annualmanagement costs in addition to the crop losses it causes. Because of extensive andfrequent use of conventional insecticides, this pest has developed serious resistance tomany classes of insecticides.In this paper, effects of fenvalerate, spinosad and azadirachtin of differentconcentration on Juvenile Hormone Esterase(JHE) activity of third instar larvae of DBMfed with different host were measured by radiochemistry (RC) method. And the growthindex of the DBM which dealt with these three insecticides was investigated, for example,pupation, emergence, mean number of eggs, and so on. The EAG reaction of the virginDBM and mating DBM dealt with insecticides of different concentration to the essentialoils extracted from the leaves of host were investigated too. The results showed that theseinsecticides acted significantly on DBM.1. The effects of Pyrethroifls to DBM of different hostThe DBM fed with different host was dealt with fenvalerate. The results showed thatfenvalerate acted soon and high concentration of it acted strongly on JHE activity of thelarvae of DBM. The growth index showed that fenvalerate acted significantly on DBM,including prolonged 4th instar and pupa period, lower pupation and eclosion ratescompared with CK, and it was positive correlation between the effects and concentrationof fenvalerate. There was no significant diversity among growth index of CK fed withdifferent host. But the DBM fed with different host which dealt with same concentration possessed significant diversity except female rate. It indicated that the adaptability ofDBM fed with different host to the fenvalerate was different.2. The effects of Spinosad to DBM of different hostThe DBM fed with different host was dealt with spinosad. The results showed that theJHE activity of LC₂₀ group was close to CK whereas the LC₅₀, LC₈₀ groups weresignificantly different from CK. The DBM dealt with spinosad possessed significantlybiological disadvantages, including prolonged 4th instar and pupa period, lighter pupaweight, lower pupation, eclosion and oviposition rates compared with CK. The EAGreaction of the DBM dealt with spinosad to the essential oils extracted from the leaves ofhost lower than that dealt with fenvalerate. It possibly attributed to the different mechanismof the two insecticides.3. The effects of Botanical Insecticides to DBM of different hostThe DBM fed with different host was dealt with different concentration of azadirachtinThe results showed that the effect of azadirachtin was longer than the two insecticidesmentioned hereinbefore. The JHE activity of DBM dealt with azadirachtin was differentfrom CK in the whole 48 hour. The 4th instar and pupa period of DBM dealt withazadirachtin were longer than those dealt with fenvalerate and spinosad, and ovipositionrate was lower. It was due to that the mode of action and toxicology of botanicalinsecticides was different from conventional insecticides. The azadirachtin substantiallyreduced insect growth and development, especially in larvae.