Susceptibility of Cotton Aphids(Aphis gossypii Glover) to Dichlorvos,Cyhalothrin, Fenvalerate and Methomyl in Hainan

A preliminary investigation of the susceptibility of cotton aphid to dichlorvos, cyhalothrin, fenvalerate and methomyl were made at Jinjiang, Liangyuan, Yacheng and Tongshi in Hainan Province.The results showed that the cotton aphids from different areas were obviously different in susceptibility to dichlorvos, cyhalothrin, fenvalerate and methomyl.The cotton aphid populations from Yacheng and Jinjiang were significantly tolerant to cyhalothrin, fenvalerate, methomyl and dichlorvos, and their tolerance ratios to these pesticides at LC50 were 21.86, 22.78, 17.88 and 13.93-fold in Yachen and 10.91, 12.59-, 11.47 and 13.49-fold in Jinjiang when the aphids from Liangyuan were used as the susceptible.The cotton aphids from Tongshi had a higher tolerance to cyhalothrin, fenvalerate, methomyl and dichlorvos, and their resistance ratios over the aphid populations from Liangyuan at LC50 were 1.58, 12.27, 4.45 and 2.28-fold.Furthermore, the cotton aphid populations from Yachen, Jinjiang and Tongshi had a higher heterogeneity of tolerance to cyhalothrin, fenvalerate, methomyl and dichlorvos.It is recommended that cyhalothrin, fenvalerate, methomyl and dichlorvos should be less used to control cotton aphids inHainan so as not to develop more highly tolerant cotton ahpid populations.