Regional reversion of insecticide resistance in Helicoverpa armigera (Lepidoptera: Noctuidae) is associated with the use of Bt cotton in northern China

A continuous programme for monitoring resistance of Helicoverpa armigera (Hubner) to commonly used insecticides was undertaken for assessing the impact of Bt cotton planting on the evolution of the pest resistance from 1994 to 2002 in China. The bioassay results showed that the resistance levels per year in field populations of H armigera to lambda-cyhalothrin, phoxim and endosulfan decreased, respectively, to 9-15-fold, 11-14-fold and 6-8-fold in 2001-2002 from 197-262-fold, 52-74-fold and 18-38-fold before the cultivation of Bt cotton in 1997. This significant increase in susceptibility to insecticides is expected to result in a reduction in insecticide application for H armigera control in Bt cotton. It is concluded that Bt cotton is playing an important role in the long-term management of H armigera by increasing the potential for natural and chemical control of the pest.     

Efficacy of various pyrethroid structures against a highly metabolically resistant isogenic strain of Helicoverpa armigera (Lepidoptera: Noctuidae) from China

BACKGROUND: Resistance to pyrethroids and other types of insecticides in Helicoverpa armigera (Hübner) has been documented in many countries. The isolation of specific resistance mechanisms in isogenic strains is an optimal approach to investigate cross-resistance pattern, and to validate resistance breaking pyrethroids. In this study an isogenic metabolic resistance CMR strain was successfully isolated from a field pyrethroid-resistant population of H. armigera. With this strain, cross-resistance among 19 pyrethroid insecticides with varying chemical structures was analysed. RESULTS: Resistance to pyrethroids in the CMR strain was likely to be due to enhanced oxidative metabolism. The most significant cross-resistance in the CMR strain was between pyrethroids such as fenvalerate, tau-fluvalinate and flumethrin characterised by having both phenoxybenzyl and aromatic acid moieties. Substitution of the phenoxybenzyl group with a polyfluorobenzyl group, as in tefluthrin, benfluthrin and transfluthrin, overcame most of this resistance. CONCLUSION: The findings in this study support the assertion that it is possible to find pyrethroids that are active against resistant populations. Such pyrethroids could be considered as possible partners or resistance breaking pyrethroids in a pyrethroid resistance management programme for H. armigera in China and in other Asian countries where the oxidative metabolism resistance is a dominant mechanism.     

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     

Selection and heritability of resistance to Bacillus thuringiensis subsp kurstaki and transgenic cotton in Helicoverpa armigera (Lepidoptera: Noctuidae)

Compared with an unselected susceptible population, a cotton bollworm, Helicoverpa armigera (Hübner), population selected for 22 generations with transgenic cotton leaves (modified Cry1A) in the laboratory developed 11.0-fold resistance to Cry1Ac (one single-protein product MVPII). Resistance to Bacillus thuringiensis Berliner subsp kurstaki (Btk) was selected for 22 generations with a 5.2-fold increase in LC50. The estimated realized heritabilities (h2) of resistance for transgenic-cotton- and Btk-selected populations were 0.1008 and 0.2341, respectively. This reflects the higher phenotypic variation in response to Cry1Ac in the transgenic-cotton-selected population. This variation may have been caused by differences in protein toxin levels expressed in different growth stages of the transgenic cotton. Because of the different slopes of the probit regression lines between Cry1Ac and Btk, the estimated realized h2 cannot be used visually to compare resistance development to Cry1Ac and Btk in H armigera. Thus, the response quotient (Q) of resistance was also estimated. The Q values of resistance for transgenic-cotton- and Btk-selected populations were 0.0763 and 0.0836, respectively. This showed that the rate of resistance development would be similar in both selection populations. This result indicates that the selection of resistance using transgenic cotton is different from that selected using the single toxin. Resistance risk to transgenic cotton and Btk in field populations was assessed assuming different pressures of selection by using the estimated h2. Assuming the h2 of resistance in a field population was half of the estimated h2, and the population received prolonged and uniform exposure to transgenic cotton or Btk causing >70% mortality in each generation, we predicted that resistance would increase 10-fold after <23 generations for Cry1Ac in transgenic cotton-selected-populations and after <21 generations for Btk in Btk-selected populations. Cross-resistance would be expected after <48 generations for Btk in transgenic-cotton-selected populations and after <21 generations for Cry1Ac in Btk-selected population. The results show that the potential to evolve resistance is similar in both transgenic-cotton- and Btk-selected populations, but that cross-resistance development to Btk is slower in transgenic-cotton-selected populations than cross-resistance development to Cry1Ac in Btk-selected populations.     

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     

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.     

Expression and inheritance of nerve insensitivity resistance in larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) from China

Nerve insensitivity resistance to synthetic pyrethroids was detected in a resistant field strain (JSFX-R) of the cotton bollworm, Helicoverpa armigera (Hübner), using a neurophysiological assay in which extracellular spontaneous neuronal activity was measured in response to cis-cypermethrin. The nerve insensitivity mechanism was selected using a combination of toxicological and neurophysiological methods. The third-instar larvae in selected strains of Family-37 and CTR strain expressed a very high resistance to fenvalerate (RF = 2060-fold and 805-fold, respectively) and high cross-resistance to DDT (RF = 1927-fold and 2384-fold, respectively) which was not affected by two metabolic synergists, PBO and DMC. The frequency of nerve-insensitive individuals detected in neurophysiological assays (54, 81 and 100% for JSFX-R strain, and the selected strains Family-43 and Family-37, respectively) was not only positively correlated (R² = 0.968) with the frequency of non-PBO-synergisable resistant individuals detected in toxicological tests (37.5, 62.5 and 90% for JSFX-R strain, Family-43 and Family-37, respectively), but also positively correlated (R² = 0.978) with the frequency of DDT-resistant individuals detected in toxicological tests (40, 67.5 and 93.3% for JSFX-R strain, Family-43 and Family-37, respectively). Analysis of dose–mortality lines to DDT and fenvalerate from F₁ hybrids (R♀ × S♂) indicated that nerve insensitivity resistance to DDT and fenvalerate in the CTR strain was inherited in an incompletely recessive pattern. Degree of dominance (D) was estimated to be −0.66 (± 0.06) (DDT) and −0.26 (± 0.04) (fenvalerate). The dose–mortality curves to DDT in back-cross progeny were strongly suggested, by chi-square analysis, to be fitted with those expected of a one-gene model. Evidence for the co-existence of nerve insensitivity and oxidative metabolic resistance mechanisms within individual H armigera and the effects of their interaction on the expression of resistance to fenvalerate are discussed. © 1999 Society of Chemical Industry     

Impact of seed blend and structured maize refuge on Helicoverpa zea (Lepidoptera: Noctuidae) potential phenological resistance development parameters in pupae and adults

BACKGROUND

Helicoverpa zea, an economic pest in the south-eastern United States, has evolved practical resistance to Bacillus thuringiensis (Bt) Cry toxins in maize and cotton. Insect resistance management (IRM) programs have historically required planting of structured non-Bt maize, but because of its low adoption, the use of seed blends has been considered. To generate knowledge on target pest biology and ecology to help improve IRM strategies, nine field trials were conducted in 2019 and 2020 in Florida, Georgia, North Carolina, and South Carolina to evaluate the impact of Bt (Cry1Ab + Cry1F or Cry1Ab + Cry1F + Vip3A) and non-Bt maize plants in blended and structured refuge treatments on H. zea pupal survival, weight, soil pupation depth, adult flight parameters, and adult time to eclosion.

RESULTS

From a very large sample size and geography, we found a significant difference in pupal mortality and weight among treatments in seed blends with Vip3A, implying that cross-pollination occurred between Bt and non-Bt maize ears. There was no treatment effect for pupation depth, adult flight distance, and eclosion time.

CONCLUSION

Results of this study demonstrate the potential impact of different refuge strategies on phenological development and survival of an important pest species of regulatory concern. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.