Current status of insecticide resistance in Q biotype Bemisia tabaci populations from Crete

BACKGROUND: A major problem of crop protection in Crete, Greece, is the control of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) with chemical insecticides owing to the rapid development of resistance. The aim of this study was to investigate the establishment of resistance and the underlying mechanisms to major insecticide classes with classical bioassays and known biochemical resistance markers. RESULTS: During a 2005–2007 survey, 53 Q biotype populations were collected. Application history records showed extensive use of neonicotinoids, organophosphates, carbamates and pyrethroids. High resistance levels were identified in the majority of populations (>80%) for imidacloprid (RF: 38–1958×) and α‐cypermethrin (RF: 30–600×). Low resistance levels (RF < 12) were observed for pirimiphos‐methyl. A strong correlation between resistance to imidacloprid and the number of applications with neonicotinoids was observed. Significant correlations were observed between COE and P450‐dependent monoxygenase activity with resistance to α‐cypermethrin and imidacloprid respectively. A propoxur‐based AChE diagnostic test indicated that iAChE was widespread in most populations. Resistance levels for α‐cypermethrin were increased when compared with a previous survey (2002–2003). Differentiation of LC₅₀ values between localities was observed for imidacloprid only. CONCLUSION: Bemisia tabaci resistance evolved differently in each of the three insecticides studied. Imidacloprid resistance seems less established and less persistent than α‐cypermethrin resistance. The low resistance levels for pirimiphos‐methyl suggest absence of cross‐resistance with other organophosphates or carbamates used. Copyright © 2008 Society of Chemical Industry     

Resistance of Bemisia tabaci (Homoptera: Aleyrodidae) to insecticides in southern Spain with special reference to neonicotinoids

The tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) which occurs in various parts of the world, has developed a high degree of resistance against several chemical classes of insecticide, including organophosphates, carbamates, pyrethroids, insect growth regulators and chlorinated hydrocarbons. The present studies were done in order to monitor the susceptibility of whitefly populations in southern Spain to insecticides commonly used there. Systemic bioassays using Spanish field populations of B tabaci collected in 1994, 1996 and 1998 indicated an increase, albeit a slow one, in resistance to imidacloprid over this period. Comparative studies of other neonicotinoids using the same bioassay revealed a high degree of cross‐resistance to acetamiprid and thiamethoxam. Leaf‐dip bioassays with adult females from these populations revealed a high level of resistance to cyfluthrin, endosulfan, monocrotophos, methamidophos, and pymetrozine, each at 200 mg litre⁻¹. Buprofezin and pyriproxyfen were tested against second‐instar nymphs and eggs, respectively. Buprofezin also showed a lower efficacy against ESP‐98, a strain of B tabaci received from Almeria in 1998, but pyriproxyfen resistance was not obvious when tested against eggs of strain ESP‐98. Field trials in 1998 revealed good efficacy of imidacloprid in one farm in the Almeria region and two greenhouses in Murcia and Sevilla, but a loss of activity by imidacloprid in another farm in the Almeria region. Cross‐resistance between imidacloprid and thiamethoxam was also confirmed under field conditions. © 2000 Society of Chemical Industry     

Induction effects of host plants on insecticide susceptibility and detoxification enzymes of Bemisia tabaci (Hemiptera: Aleyrodidae)

BACKGROUND: The polyphagous B‐biotype Bemisia tabaci (Gennadius) has developed a high resistance to commonly used insecticides in China. To illustrate the induced changes by host plant, bioassay and biochemical research on five different host populations were investigated. RESULTS: Except for bifenthrin, all tested insecticides showed lower toxicity to the B. tabaci poinsettia population compared with other host populations. Moreover, four insecticides, the exceptions being abamectin and fipronil, showed highest toxicity towards the tomato population. The LC₅₀ values of the poinsettia population, particularly towards acetamiprid, were 14.8‐, 10.3‐ and 7.29‐fold higher than those of tomato, cucumber and cabbage respectively. The CarE activities of B. tabaci cabbage and cucumber populations were all significantly higher than those of poinsettia, cotton and tomato populations. The ratio of the cabbage population was 1.97‐, 1.79‐ and 1.30‐fold higher than that of poinsettia, cotton and tomato respectively. The frequency profiles for this activity also have obvious differences. The GST and P450 activities of the cucumber population were the lowest in the five host populations. CONCLUSION: Long‐term induction of host plants for B‐biotype B. tabaci could influence their susceptibilities to several insecticides. Rational selection and usage of insecticides for particular hosts will be helpful for resistance management and control of this species. Copyright © 2010 Society of Chemical Industry     

Biotype and insecticide resistance status of the whitefly Bemisia tabaci from China

BACKGROUND: Resistance to numerous insecticide classes in Bemisia tabaci Gennadius has impaired field control efficacy in south‐eastern China. The biotype and resistance status of B. tabaci collected from these areas was investigated. RESULTS: Two different biotypes of B. tabaci (B‐biotype and Q‐biotype) were detected in south‐eastern China, and the samples collected from geographical regions showed a prevalence of the Q‐biotype and the coexistence of B‐ and Q‐biotypes in some regions. Moderate to high levels of resistance to two neonicotinoids were established in both biotypes (28–1900‐fold to imidacloprid, 29–1200‐fold to thiamethoxam). Medium to high levels of resistance to alpha‐cypermethrin (22–610‐fold) were also detected in both biotypes. Four out of 12 populations had low to medium levels of resistance to fipronil (10–25‐fold). Four out of 12 populations showed low levels of resistance to spinosad (5.7–6.4‐fold). All populations tested were susceptible to abamectin. CONCLUSION: The Q‐biotype B. tabaci is supplanting the B‐biotype which used to be ubiquitous in China. Field populations of both B‐ and Q‐biotypes of B. tabaci have developed high levels of resistance to imidacloprid and thiamethoxam. Abamectin is the most effective insecticide against adult B. tabaci from all populations. Copyright © 2010 Society of Chemical Industry     

The role of B‐type esterases in conferring insecticide resistance in the tobacco whitefly,Bemisia tabaci (Genn)

Separation of non‐specific esterases on electrophoretic gels has played a key role in distinguishing between races or biotypes of the tobacco whitefly, Bemisia tabaci. One intensively staining esterase in particular (termed E_0.14) has assumed significance as a diagnostic of B‐type whiteflies (aka Bemisia argentifolii), despite any knowledge of its biological function. In this study, a whitefly strain (B‐Null) homozygous for a null allele at the E_0.14 locus that had been isolated from a B‐type population was used to demonstrate a significant role for E_0.14 in resistance of B‐type populations to pyrethroids but not to organophosphates (OPs). Bioassays with pyrethroids, following pre‐treatment with sub‐lethal doses of the OP profenofos (to inhibit esterase activity), coupled with metabolism studies with radiolabelled permethrin, supported the conclusion that pyrethroid resistance in a range of B‐type strains expressing E_0.14 was primarily due to increased ester hydrolysis. In the same strains, OP resistance appeared to be predominantly conferred by a modification to the target‐site enzyme acetylcholinesterase. © 2000 Society of Chemical Industry     

Cross‐resistance,inheritance and biochemical mechanisms of imidacloprid resistance in B‐biotype Bemisia tabaci

BACKGROUND: The B‐type Bemisia tabaci (Gennadius) has become established in many regions in China, and neonicotinoids are extensively used to control this pest. Imidacloprid resistance in a laboratory‐selected strain of B‐type B. tabaci was characterised in order to provide the basis for recommending resistance management tactics. RESULTS: The NJ‐Imi strain of B‐type B. tabaci was selected from the NJ strain with imidacloprid for 30 generations. The NJ‐Imi strain exhibited 490‐fold resistance to imidacloprid, high levels of cross‐resistance to three other neonicotinoids, low levels of cross‐resistance to monosultap, cartap and spinosad, but no cross‐resistance to abamectin and cypermethrin. Imidacloprid resistance in the NJ‐Imi strain was autosomal and semi‐dominant. It is shown that enhanced detoxification mediated by cytochrome‐P450‐dependent monooxygenases contributes to imidacloprid resistance to some extent in the NJ‐Imi strain. Results from synergist bioassays and cross‐resistance patterns indicated that target‐site insensitivity may be involved in imidacloprid resistance in the NJ‐Imi strain of B. tabaci. CONCLUSION: Although oxidative detoxification mediated by P450 monooxygenases is involved in imidacloprid resistance in the NJ‐Imi strain of B‐type B. tabaci, target‐site modification as an additional resistance mechanism cannot be ruled out. Considering the high risk of cross‐resistance, neonicotinoids should be regarded as a single group when implementing an insecticide rotation scheme in B. tabaci control. Copyright © 2009 Society of Chemical Industry     

Cross‐resistance relationships between neonicotinoids and pymetrozine in Bemisia tabaci (Hemiptera: Aleyrodidae)

BACKGROUND: Although cross‐resistance between compounds in the same insecticide group is a frequently observed phenomenon, cross‐resistance between groups that differ in structural and functional characteristics can be extremely unpredictable. In the case of controlling the whitefly, Bemisia tabaci Gennadius, neonicotinoids and the pyridine azomethine antifeedant pymetrozine represent independent lines of discovery that should be suited for alternation to avoid prolonged selection for the same resistance mechanism. Reports of an association between responses to neonicotinoids and pymetrozine were investigated by resistance profiling of seven B. tabaci strains and complementary reciprocal selection experiments. RESULTS: All strains demonstrated a consistent correlation between responses to three neonicotinoid compounds: thiamethoxam, imidacloprid and acetamiprid. Responses to neonicotinoids for six field strains clearly correlated with responses to pymetrozine. Reciprocal selection experiments confirmed an unexpected case of intergroup cross‐resistance. A seventh strain exhibited a so far unique phenotype of strong resistance to pymetrozine but full susceptibility to neonicotinoids. Selection experiments confirmed that in this strain the mechanism of pymetrozine resistance is specific and has no implications for neonicotinoids. CONCLUSION: Cross‐resistance between neonicotinoids and pymetrozine in B. tabaci probably reflects the overexpression of a cytochrome‐P450‐dependent monooxygenase capable of metabolising both types of compound in spite of their apparent structural dissimilarity. Given the predominance of this mechanism in B. tabaci, both can contribute to resistance management but should be placed within the same treatment ‘window’. Copyright © 2010 Society of Chemical Industry     

Insecticide resistance management of Bemisia tabaci (Hemiptera: Aleyrodidae) in Australian cotton – pyriproxyfen,spirotetramat and buprofezin

BACKGROUND

Bemisia tabaci is a globally significant agricultural pest including in Australia, where it exhibits resistance to numerous insecticides. With a recent label change, buprofezin (group 16), is now used for whitefly management in Australia. This study investigated resistance to pyriproxyfen (group 7C), spirotetramat (group 23) and buprofezin using bioassays and available molecular markers.

RESULTS

Bioassay and selection testing of B. tabaci populations detected resistance to pyriproxyfen with resistance ratios ranging from 4.1 to 56. Resistance to spirotetramat was detected using bioassay, selection testing and sequencing techniques. In populations collected from cotton, the A2083V mutation was detected in three populations of 85 tested, at frequencies ≤4.1%, whereas in limited surveillance of populations from an intensive horticultural region the frequency was ≥75.8%. The baseline susceptibility of B. tabaci to buprofezin was determined from populations tested from 2019 to 2020, in which LC₅₀ values ranged from 0.61 to 10.75 mg L⁻¹. From the bioassay data, a discriminating dose of 200 mg L⁻¹ was developed. Recent surveillance of 16 populations detected no evidence of resistance with 100% mortality recorded at doses ≤32 mg L⁻¹. A cross-resistance study found no conclusive evidence of resistance to buprofezin in populations with high resistance to pyriproxyfen or spirotetramat.

CONCLUSIONS

In Australian cotton, B. tabaci pest management is challenged by ongoing resistance to pyriproxyfen, while resistance to spirotetramat is an emerging issue. The addition of buprofezin provides a new mode-of-action for whitefly pest management, which will strengthen the existing insecticide resistance management strategy. © 2023 Commonwealth of Australia. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Monitoring neonicotinoid resistance in biotype B of Bemisia tabaci in Florida

BACKGROUND: Biotype B of the sweetpotato whitefly, Bemisia tabaci (Genn.), is a worldwide pest that has developed resistance to many insecticides, including the neonicotinoid class. Florida field populations were monitored for susceptibility to the neonicotinoids imidacloprid and thiamethoxam using a cut leaf petiole bioassay method. RESULTS: Average RR₅₀ values for imidacloprid increased from 3.7 in 2000 to 12.0 in 2003; decreased to 5.0 and 2.5 in 2004 and 2005, respectively; and then increased to 26.3 and 23.9 in 2006 and 2007, respectively. Populations with RR₅₀ values of about 50 to 60 during generation one reverted to RR₅₀ values of ?4 in six generations, when reared without further exposure to imidacloprid. Average RR₅₀ values for thiamethoxam increased from 2.0 in 2003 to 24.7 in 2006 and decreased to 10.4 in 2007. Populations with RR₅₀ values of about 22, 32 and 53 during generation one declined to 8, 5 and 6, respectively, after being reared for five generations without exposure to thiamethoxam. The correlation coefficient from the 26 populations that were bioassayed both with imidacloprid and thiamethoxam showed a significant positive correlation (R² = 0.58) between these populations. CONCLUSION: The high level of RR₅₀ values to imidacloprid and thiamethoxam suggest an unstable decline in the susceptibility of B. tabaci to imidacloprid and thiamethoxam, with possible cross‐resistance or predisposition for dual resistance selection. Copyright © 2009 Society of Chemical Industry     

Susceptibility to neonicotinoids and risk of resistance development in the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

BACKGROUND: In recent years, outbreaks of the brown planthopper, Nilaparvata lugens (Stål), have occurred more frequently in China. The objective of this study was to determine the susceptibility of N. lugens to neonicotinoids and other insecticides in major rice production areas in China. RESULTS: Results indicated that substantial variations in the susceptibility to different insecticides existed in N. lugens. Field populations had developed variable resistance levels to neonicotinoids, with a high resistance level to imidacloprid (RR: 135.3–301.3‐fold), a medium resistance level to imidaclothiz (RR: 35–41.2‐fold), a low resistance level to thiamethoxam (up to 9.9‐fold) and no resistance to dinotefuran, nitenpyram and thiacloprid (RR < 3‐fold). Further examinations indicated that a field population had developed medium resistance level to fipronil (up to 10.5‐fold), and some field populations had evolved a low resistance level to buprofezin. In addition, N. lugens had been able to develop 1424‐fold resistance to imidacloprid in the laboratory after the insect was selected with imidacloprid for 26 generations. CONCLUSION: Long‐term use of imidacloprid in a wide range of rice‐growing areas might be associated with high levels of resistance in N. lugens. Therefore, insecticide resistance management strategies must be developed to prevent further increase in resistance. Copyright © 2008 Society of Chemical Industry     

Relative abundance of Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) and its parasitoids,and the impact of augmentative release of Eretmocerus spp. (Hymenoptera: Aphelinidae) on the population dynamics of the pest in Burkina Faso (West Africa)

Whitefly infestations and parasitism were monitored year-round in overlapping cotton crops sown on three dates in Burkina Faso. The relative abundance of B. tabaci (Gennadius) and its parasitoids, Eretmocerus spp. and Encarsia spp., was recorded in control and insecticide-sprayed plots. Low B. tabaci populations developed during the first half of the rainy season. Pest populations increased when rainfall was ending, and the levels reached were higher in insecticide-treated plots (48 nymphs/leaf) than in control plots (25 nymphs/leaf). Parasitism reached 88.7% in control plots, and 53.7% in insecticide-treated plots. Eretmocerus spp. nymphs were more abundant than Encarsia spp. in both treated and control plots. A positive and significant curvilinear relationship was observed where % parasitism, on a linear scale, rose to a plateau with logarithmic increase in host density. In general % parasitism was correlated with the abundance of pest populations except in March and April where parasitism increased while B. tabaci populations decreased. In a separate experiment, adult Eretmocerus spp. were released into caged cotton plants to study the impact of augmentative releases of the parasites on the population dynamics of the pest. Pest densities increased from 1.47 nymphs/leaf to 39.4 nymphs/leaf in the control, but were reduced to 0.8 and 0.6 nymphs/leaf in the cages where, respectively, 4 and 8 parasitoids were released per plant. It appears that parasitism is an important factor reducing B. tabaci populations during and after the cotton-growing season, and that Eretmocerus spp. are promising biological control candidates against the pest in cotton.     

Biological characterization of sulfoxaflor, a novel insecticide

BACKGROUND: The commercialization of new insecticides is important for ensuring that multiple effective product choices are available. In particular, new insecticides that exhibit high potency and lack insecticidal cross‐resistance are particularly useful in insecticide resistance management (IRM) programs. Sulfoxaflor possesses these characteristics and is the first compound under development from the novel sulfoxamine class of insecticides. RESULTS: In the laboratory, sulfoxaflor demonstrated high levels of insecticidal potency against a broad range of sap‐feeding insect species. The potency of sulfoxaflor was comparable with that of commercial products, including neonicotinoids, for the control of a wide range of aphids, whiteflies (Homoptera) and true bugs (Heteroptera). Sulfoxaflor performed equally well in the laboratory against both insecticide‐susceptible and insecticide‐resistant populations of sweetpotato whitefly, Bemisia tabaci Gennadius, and brown planthopper, Nilaparvata lugens (Stål), including populations resistant to the neonicotinoid insecticide imidacloprid. These laboratory efficacy trends were confirmed in field trials from multiple geographies and crops, and in populations of insects with histories of repeated exposure to insecticides. In particular, a sulfoxaflor use rate of 25 g ha^?1 against cotton aphid (Aphis gossypii Glover) outperformed acetamiprid (25 g ha^?1) and dicrotophos (560 g ha^?1). Sulfoxaflor (50 g ha^?1) provided a control of sweetpotato whitefly equivalent to that of acetamiprid (75 g ha^?1) and imidacloprid (50 g ha^?1) and better than that of thiamethoxam (50 g ha^?1). CONCLUSION: The novel chemistry of sulfoxaflor, its unique biological spectrum of activity and its lack of cross‐resistance highlight the potential of sulfoxaflor as an important new tool for the control of sap‐feeding insect pests. Copyright © 2010 Society of Chemical Industry     

Incidence and characterisation of resistance to neonicotinoid insecticides and pymetrozine in the greenhouse whitefly,Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae)

BACKGROUND: Trialeurodes vaporariorum (Westwood), also known as the greenhouse whitefly, is a serious pest of protected vegetable and ornamental crops in most temperate regions of the world. Neonicotinoid insecticides are used widely to control this species, although resistance has been reported and may be becoming widespread. RESULTS: Mortality rates of UK and European strains of T. vaporariorum to a range of neonicotinoids and pymetrozine, a compound with a different mode of action, were calculated, and significant resistance was found in some of those strains. A strong association was found between neonicotinoids and pymetrozine, and reciprocal selection experiments confirmed this finding. Expression of resistance to the neonicotinoid imidacloprid and pymetrozine was age specific, and resistance in nymphs did not compromise recommended application rates. CONCLUSION: This study indicates strong parallels in the phenotypic characteristics of neonicotinoid resistance in T. vaporariorum and the tobacco whitefly Bemisia tabaci Gennadius, suggesting possible parallels in the underlying mechanisms. Copyright © 2010 Society of Chemical Industry     

天津市烟粉虱隐种鉴定及其携带TYLCV、内共生菌情况和抗药性监测

为明确天津市烟粉虱Bemisia tabaci隐种的类别及其寄主适应性、传毒能力、携带内共生菌情况和抗药性,采用mt COI酶切法对从武清、西青、蓟州和宁河4个区的番茄、黄瓜及辣椒3种寄主上采集的12个烟粉虱种群进行隐种鉴定,采用PCR检测其携带番茄黄化曲叶病毒（tomato yellow leaf curl virus,TYLCV）和内共生菌情况,并采用浸叶法测定其对4种常用药剂的抗性。结果表明,采集的烟粉虱种群以MED隐种为主,占所有检测个体的93.33%,有3个种群为MED和MEAM1隐种混合发生。所有检测个体中有36.25%的个体携带TYLCV,在6个种群中检测到TYLCV,其中5个种群有超过50%的个体携带TYLCV。在12个种群中共检测到Hamiltonella、立克次氏体Rickettsia、Cardinium和杀雄菌属Arsenophnus共4种内共生菌,携带个体比例分别为90.63%、48.96%、43.75%和8.33%,进一步对内共生菌协同感染情况进行分析,发现有HARC、HRC、HAC、HR、HC和AC共6个协同感染型,感染率分别为4.17%、28.13%、3....     

Control strategy for the sweetpotato whiteflyBemisia tabaci,late in the cotton-growing season

Populations of the sweetpotato whitefly,Bemisia tabaci (Gennadius), were sampled late in the cotton-growing seasons of 1990, 1991 and 1992, in commercial ‘Acala’ cotton fields in southwestern Israel. In mid summer, when populations ofB. tabaci started to build up, cotton fields were commercially treated with a single application of an IGR (insect growth regulator). The experimental plots were then treated in September with conventional adulticides or with the novel insecticides buprofezin and pyriproxyfen (IGR), and diafenthiuron (a thiourea derivative). The effects of the insecticides onB. tabaci larval and adult populations, and the amount of damage to the cotton lint, were recorded. Untreated populations of larvae and pupae ofB. tabaci in the three end-of-season studies, had the tendency to build up toward the defoliation treatment. However, the level of theB. tabaci populations observed in the experimental fields and the short period of exposure of the open cotton bolls to the whiteflies, did not result in lint damage, probably because the whitefly numbers had been reduced considerably after the defoliation treatment. At the end of the 1991 and 1992 cotton seasons, a high level of parasitism, ranging between 50% and 80%, was recorded. The shift in chemical applications toward the novel IGRs during the season, along with the reduction in insecticide use in general, probably contributed to the propagation of parasitoids, thereby improving whitefly control.     

Pyrethroid insecticide resistance in British populations of the cabbage whitefly, Aleyrodes proletella

BACKGROUND: The cabbage whitefly, Aleyrodes proletella L., is emerging as a significant pest of field brassica crops in certain regions of the United Kingdom. In order to investigate the contribution of pesticide resistance to this phenomenon, A. proletella populations were sampled from five different areas in England in 2008 and 2009. Adult residual leaf‐dip bioassays were carried out using pyrethroid and neonicotinoid insecticides. RESULTS: Significant resistance to pyrethroids was found in multiple samples collected from two areas. No evidence of cross‐resistance to neonicotinoids was found in a subset of the pyrethroid‐resistant populations. While the patterns of resistance to different pyrethroids were broadly correlated, the magnitude of resistance factors differed substantially. Survival of strains at a putative diagnostic concentration of lambda‐cyhalothrin was found to provide a guide to their LC₅₀. Significant differences in LC₅₀ were found when different brassica crops were used in the bioassay, although the resistance patterns between strains were maintained. CONCLUSION: Reduced susceptibility to multiple pyrethroid insecticides exists in populations of A. proletella in the United Kingdom, corresponding to recent major outbreaks. The mechanism(s) of resistance are yet to be determined, but molecular structural differences in pyrethroids probably influence the magnitude of cross‐resistance within this group of insecticides. Copyright © 2011 Society of Chemical Industry     

Management of resistance in Bemisia in Arizona cotton

A whitefly (Bemisia argentifolii) resistance crisis climaxed in 1995 in Arizona cotton and prompted the development of an integrated resistance management strategy adapted from a program implemented in Israel in 1987. The strategy incorporated two new major elements: once-per-year use of the insect growth regulators (IGRs) pyriproxyfen and buprofezin, and measures to delay use of pyrethroids for as long into the growing season as possible. A three-stage chemical use recommendation was formulated comprising IGRs (Stage I), other non-pyrethroid insecticides (Stage II), and synergized pyrethroid insecticides (Stage III). Results from use of the strategy in the 1996 season were very promising. Insecticide use for control of whiteflies was reduced substantially. State-wide monitoring of whitefly susceptibility revealed significant reductions in resistance to synergized pyrethroids as well as increased susceptibility to amitraz. Susceptibility of Lygus bugs to key insecticides changed correspondingly with increases and decreases in whitefly resistance from 1994 through 1996. ©1997 SCI     

Screening insecticides against the tobacco whitefly (Bemisia tabaci) on cotton,using a leaf cage laboratory method

Over 20 insecticides were screened against the tobacco whitefly,Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), on cotton. AsB. tabaci feeds only on live plants, a suitable laboratory test method incorporating young cotton plants was developed. Both cover sprays and systemic insecticides applied to the soil were tested. Triazophos, pyridaphenthion, azinphos-methyl, bendiocarb and flucythrinate were found to be effective and persistent. The best of the systemic insecticides was aldicarb, followed by butocarboxim.     

Pyriproxyfen,a novel insect growth regulator for controlling whiteflies: Mechanisms and resistance management

Pyriproxyfen, a novel juvenile hormone mimic, is a potent suppressor of embryogenesis and adult formation of the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Dipping of cotton or tomato seedlings infested with 0 to 1-day-old eggs in 0.1 mg litre^?1 resulted in over 90% suppression of egg hatch of both B. tabaci and T. vaporariorum. Older eggs were affected to a lesser extent. Exposure of whitefly females to cotton or tomato seedlings treated with pyriproxyfen resulted in oviposition of non-viable eggs. The LC90 values for egg viability of B. tabaci and T. vaporariorum exposed to treated plants were 0.05 and 0.2 mg litre^?1, respectively. Treatment of whitefly larvae with 0.04–5 mg litre^?1 resulted in normal development until the pupal stage; however, adult emergence was totally suppressed. Second instars of B. tabaci exposed to 5 mg litre^?1 pyriproxyfen, excreted honeydew at a level similar to the control level until the fourth instar (pupation), after which a strong reduction was observed. Inhibition of egg-hatch on the lower surface of cotton leaves was observed when their upper surface was treated with 1–25 mg litre^?1, indicating a pronounced translaminar effect. These findings indicate that pyriproxyfen is an efficient control agent of both B. tabaci and T. vaporariorum. The compound has been used successfully for controlling whiteflies in Israeli cotton fields since 1991. Adults of B. tabaci collected from a rose greenhouse and from adjacent cotton fields were monitored during 1991–1993 for their susceptibility to pyriproxyfen. A high level of resistance was recorded in whiteflies collected from a greenhouse after three successive applications of pyriproxyfen. Based on LC50 values, the resistance ratio for egg-hatch suppression was 554-fold and, for adult emergence failure, 10-fold. However, a single treatment of pyriproxyfen in cotton fields during the summer season (according to an insecticide resistance management (IRM) strategy) did not alter appreciably the susceptibility of B. tabaci to this compound. In order to prevent development of resistance, an attempt should be made to restrict its use to one treatment per crop season applied during the peak activity of the pest. Pyriproxyfen can be alternated with other novel compounds such as buprofezin and diafenthiuron for controlling whiteflies in cotton, vegetables and ornamentals as part of integrated pest management (IPM) and IRM strategies. In pyriproxyfen- or buprofezin-resistant strains of B. tabaci or T. vaporariorum, no appreciable cross-resistance was observed among pyriproxyfen, buprofezin and diafenthiuron.     

High-throughput allelic discrimination of B and Q biotypes of the whitefly, Bemisia tabaci, using TaqMan allele-selective PCR

BACKGROUND: B and Q biotypes of the whitefly, Bemisia tabaci (Gennadius), are generally regarded as the most significant given their global distribution and strong resistance to insecticides. Since these biotypes can coexist and differ markedly in their insecticide resistance profiles, a rapid but reliable means of discriminating between them would be a valuable complement to resistance monitoring and management programmes. Recently, PCR‐based methods have been developed to determine the biotype status of B. tabaci populations. However, these require post‐amplification procedures, which increase time and labour. RESULTS: The authors have developed an allelic discrimination real‐time PCR assay using fluorescent dye‐labelled probes to distinguish the B and Q biotypes. The assay targets a single nucleotide polymorphism (SNP) in the mitochondrial cytochrome oxidase I (mtCOI) gene. To evaluate the assay, DNA was extracted from individual whiteflies of six known biotype strains, and all scored correctly as either a B or Q biotype. As further validation, 72 individuals from field samples collected in different parts of the world were also tested by the assay. No failed reactions were observed, with all 72 samples scoring clearly as either the B or Q biotype. CONCLUSION: The development of this rapid and high‐throughput assay has important potential for routine monitoring of B and Q biotypes on ornamental plants and for the screening of B. tabaci populations in countries where these biotypes are not yet established. Copyright © 2007 Society of Chemical Industry