Dynamics of pyrethroid resistance in a field population of Helicoverpa armigera (Hübner) in China

Dynamics of pyrethroid resistance in a field population of cotton bollworm (Helicoverpa armigera) was demonstrated by continuous monitoring with twin discriminating dosages, and the influencing factors were also experimentally analysed. Resistance in a field population in China increased rapidly in the 3rd and 4th generations when population density became higher and insecticides were applied repeatedly, then decreased suddenly during over-wintering and slowly in the 1st and 2nd generations when insecticide spraying was suspended. Resistance increase could be countered by dilution as a result of immigration of susceptible moths from corn fields, which were found to be a natural refuge for this pest in China. The reduction of resistance during over-wintering and the 1st and 2nd generations was affected by the lower fitness of resistant cotton bollworms to low temperature and disadvantages in reproduction. The possibilities of managing the resistance in field populations on the basis of these observations are discussed. © 1999 Society of Chemical Industry     

Insensitive acetylcholinesterase causes resistance to organophosphates in Australian Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Organophosphates are valuable insecticides used to control Helicoverpa armigera on cotton in Australia. Those most commonly used for Helicoverpa spp. control are pro-fenofos, parathion-methyl and chlorpyrifos. However, there is an emerging organophosphate-resistance threat in Australian H. armigera, which is compounded by cross-resistance between profenofos and parathion-methyl. An insensitive acetylcholinesterase has been identified as the common resistance mechanism. No resistance to chlorpyrifos has been detected and acetylcholinesterase remains fully sensitive to the chlorpyrifos oxon. © 1998 Society of Chemical Industry     

Pyrethroid resistance in the cotton bollworm,Helicoverpa armigera (Hübner), in West Africa

The susceptibility of Helicoverpa armigera to pyrethroids has been investigated in West Africa by means of laboratory bioassays since 1985, the first year of widespread pyrethroid use. For some years, this survey has shown a tendency for the pest to become more tolerant to pyrethroids. During the 1996 growing season, farmers using calendar‐based spraying programmes reported control failures in various countries. The strong efficacy of cypermethrin on small larvae was confirmed in experimental plots, but the effect decreased quickly in successive instars. Bioassays performed on resistant strains revealed an increase in LD₅₀ that was related to different resistance mechanisms. Metabolic resistance (MFO) appears to be a possible primary mechanism of resistance to pyrethroids. Target modification (kdr) is involved to a small degree and esterases seem to appear only after additional selection pressure. © 2000 Society of Chemical Industry     

Linkage of genes for sodium channel and cytochrome P450 (CYP6B10) in Heliothis virescens

Genetic linkage of hscp (heliothis sodium channel protein) and CYP6B10 was discovered in Heliothis virescens. The hscp gene encodes the sodium channel target of pyrethroid insecticides and cytochrome P450 genes encode important enzymes involved in detoxication of various pesticides. Previously, two mechanisms, nerve insensitivity due to sodium channel and synergism by propynyl aryl ethers, were observed in pyrethroid-resistant H virescens and were not separated by repeated back-crossing. We hypothesized genetic linkage of target site insensitivity and monooxygenase-mediated detoxication. Single nucleotide polymorphisms were discovered in IIS6 of hscp; Hpy of hscp and CYP6B10. Segregation of these and other markers was tested in backcrosses. We observed cosegregation of hscp to CYP6B10, but both genes assorted independently of y, ye and sex. Genes y and ye assorted independently of each other. This was the first observation of linkage between genes controlling detoxication and sodium ion channel insensitivity in a species known to express high levels of pyrethroid resistance. Linkage was not likely because this species has 31 chromosomes; therefore, we will investigate the possibility of a resistance cassette. We expect similar linkage in other noctuid pests.     

Effect of pretreatment with piperonyl butoxide on pyrethroid efficacy against insecticide-resistant Helicoverpa armigera (Lepidoptera: Noctuidae) and Bemisia tabaci (Sternorrhyncha: Aleyrodidae)

Pyrethroid resistance in B-type Bemisia tabaci Gennadius and Australian Helicoverpa armigera Hübner field populations is primarily conferred by esterase isoenzymes which metabolise and sequester pyrethroid insecticides. It has been shown previously that pyrethroid resistance-associated esterases in H. armigera are inhibited by the insecticide synergist piperonyl butoxide (PBO) over a 22-h period. It is demonstrated here that similar inhibition can be obtained against B-type B. tabaci. Small-scale field trials showed excellent levels of pyrethroid control when insects were pretreated with PBO and then dosed with pyrethroid during the time of maximum esterase inhibition. These results demonstrate that PBO can restore pyrethroid efficacy in the field against both B-type B. tabaci and resistant H. armigera.     

Patterns of resistance to organophosphate insecticides in field populations of Helicoverpa armigera in Pakistan

The pattern of organophosphate resistance in field populations of Helicoverpa armigera (Hübner) was monitored in Pakistan from 1994 through 1997 using an IRAC leaf-dip method. Generally, moderate to high resistance was found to an orthophosphorate, monocrotophos and to a dithiophosphorate, ethion. Resistance to the commonly used thiophosphorates, chlorpyrifos and profenofos, was very low during 1994 and 1995 but showed an upward trend during 1996 and 1997. Resistance factors to the other thiophosphorates such as quinalphos, parathion-methyl, methamidophos and triazophos remained very low. Baseline lethal concentrations for ethion, methamidophos and triazophos were at least four to five times higher than those for the other organophosphates tested, suggesting their low intrinsic efficacy against H armigera. © 1999 Society of Chemical Industry