Dynamics of insecticide resistance in Bemisia tabaci: a case study with the insect growth regulator pyriproxyfen

The dynamics of pyriproxyfen resistance in Bemisia tabaci (Gennadius) have been studied intensively in cotton fields and greenhouses in Israel. High resistance to pyriproxyfen evolved one year after its introduction for use on flowers in greenhouses, after three successive applications. After ten years of pyriproxyfen use in cotton fields, with only one application per season, a high level of resistance was observed, but its rate of development differed among localities. It is hypothesized that these differences reflect temporal and spatial variations in the availability of alternative host plants for B tabaci, and that pyriproxyfen resistance evolved most readily in geographically isolated areas. It is also likely that the occurrence and development of resistance is partially biotype-related. Pyriproxyfen use has ceased in high-resistance localities, but in areas with low frequencies of resistance, cotton growers have continued to achieve acceptable control of B tabaci with pyriproxyfen. Due to the absence of applications of pyriproxyfen in some cotton fields, resistance levels tended to decline between 1998 and 2001. Laboratory experiments support the hypothesis that this decline reflects, in part, fitness costs associated with pyriproxyfen resistance.     

Reversal of resistance to pyriproxyfen in the Q biotype of Bemisia tabaci (Hemiptera: Aleyrodidae)

Pyriproxyfen, a juvenile hormone (JH) mimic, is a biorational insecticide that disrupts insect development. It is one of the principal insecticides being used to control Bemisia tabaci (Gennadius) on cotton, and has many environmentally positive attributes that make it compatible with integrated pest management (IPM) programs. In Israel, a high level of resistance to pyriproxyfen has been observed in several isolated regions. Here, tests were conducted to establish whether temporal refuges from exposure to pyriproxyfen could be useful for restoring the effectiveness of the compound. Resistance was found to decrease by a factor of 8 when exposure to pyriproxyfen was ceased for 13 generations. Reversal of resistance was accompanied with increased biotic fitness of the revertant colony. By incorporating experimental estimates of nymph survival, sex ratio, fecundity, egg hatching rate and developmental time, the seasonal cost per generation for resistant insects was estimated to be 25%. A genetic simulation model, optimized by empirical data from bioassays, predicted fitness cost per generation of 19% for resistant homozygous (RR) females and hemizygous (R) males, and produced rates of reversal similar to the experimental results. The model also predicted that, even after 5 years ( approximately 55 generations) without pyriproxyfen treatments, the frequency of the resistance allele (R) will still remain high (0.02). It is therefore concluded, on the basis of experimental and modeling results, that the effectiveness of temporal refuges for reversing development of resistance to pyriproxyfen in B. tabaci may be limited.     

The presence of Rickettsia is associated with increased susceptibility of Bemisia tabaci (Homoptera: Aleyrodidae) to insecticides

BACKGROUND: The presence of certain symbiotic microorganisms may be associated with insecticide resistance in insects. The authors compared the susceptibility of two isofemale lines, Rickettsia-plus and Rickettsia-free, of the sweet potato whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) to major insecticides from different chemical groups, including imidacloprid, acetamiprid, thiamethoxam, pyriproxyfen, spiromesifen and diafenthiuron. RESULTS: While the Rickettsia-plus and Rickettsia-free lines showed no differences in their susceptibility to imidacloprid and diafenthiuron, higher susceptibility of the Rickettsia-plus line to acetamiprid, thiamethoxam, spiromesifen and especially pyriproxyfen was observed. LC(90) values indicated that the Rickettsia-free line was 15-fold more resistant to pyriproxyfen than the Rickettsia-plus line. CONCLUSION: Findings indicate that the infection status of B. tabaci populations by Rickettsia is an important consideration that should be taken into account when performing resistance monitoring studies, and may help in understanding the dynamics of B. tabaci resistance, symbiont-pest associations in agricultural systems and the biological impact of Rickettsia on whitefly biology.     

The response of pyriproxyfen-resistant and susceptible Bemisia tabaci Genn (Homoptera: Aleyrodidae) to pyriproxyfen and fenoxycarb alone and in combination with piperonyl butoxide

Pyriproxyfen was effective against susceptible Bemisia tabaci eggs at a LC₅₀ of 0.003 mg litre⁻¹ and against nymphs at 0.02 mg litre⁻¹. In comparison, eggs of a laboratory selected, pyriproxyfen-resistant B tabaci strain, originating in an Israeli greenhouse, exhibited 6500-fold resistance and nymphs exhibited 1100-fold resistance. Eggs and nymphs of a strain from an Israeli sunflower field exhibited 450 and 210-fold resistance in comparison to the susceptible standard. Fenoxycarb was generally less effective than pyriproxyfen against B tabaci eggs and nymphs but was unaffected by pyriproxyfen resistance. Piperonyl butoxide (PB) was antagonistic to pyriproxyfen, and this increased with increasing pyriproxyfen resistance. PB had no effect on the toxicity of fenoxycarb. Collectively, these data imply that the modes of action of pyriproxyfen and fenoxycarb are distinct, despite the structural similarities of these molecules. Possible reasons for the antagonism of PB against pyriproxyfen are discussed. © 1999 Society of Chemical Industry     

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.     

Effect of pyriproxyfen on developing stages and embryogenesis of California red scale (CRS), Aonidiella aurantii

During the past decade, the insect growth regulator pyriproxyfen has been the most used insecticide for controlling the California red scale (CRS), Aonidiella aurantii (Maskell), an important pest in citrus groves worldwide. The aim of the present research was to develop bioassays for determining the effect of pyriproxyfen on developing stages and embryogenesis of CRS that can serve as baselines for monitoring resistance. Pyriproxyfen was very effective against first- and second-instar nymphs of a susceptible strain of CRS; 0.1 and 0.2 mg AI L(-1), resulting in 80 and 100% mortality of first-instar nymphs, and in 62.5 and 91.7% mortality of second-instar nymphs respectively. According to probit analysis, the LC(50) and LC(90) values of pyriproxyfen for first-instar nymphs were 0.03 and 0.15 mg AI L(-1), and for second-instar nymphs they were 0.05 and 0.25 mg AI L(-1) respectively. Pyriproxyfen was quite effective on first-instar nymphs of a CRS field strain originating from a citrus grove where two successive applications of the compound had been applied. Mortality rates were 86 and 100% at concentrations of 0.2 and 0.4 mg AI L(-1) respectively. Pyriproxyfen suppressed embryogenesis when CRS females were treated with pyriproxyfen. Young CRS females treated with 1.0 and 5.0 mg AI L(-1) pyriproxyfen produced 6.6 N(1)/F and 2.4 N(1)/F as compared with 10.9 N(1)/F in untreated control.     

Lack of fitness costs associated with pyriproxyfen resistance in the B biotype of Bemisia tabaci

BACKGROUND: The insect growth regulator pyriproxyfen has provided effective control of the whitefly Bemisia tabaci Gennadius in many countries. Here, whether or not fitness costs were associated with pyriproxyfen resistance in a laboratory‐selected resistant strain (QC02‐R) of the B biotype was determined. RESULTS: Mortality caused by pyriproxyfen and fitness traits over time were measured in unselected and selected hybrid strains, which were created by crossing individuals of the resistant strain with individuals of a susceptible strain. Fitness costs were not associated with resistance in QC02‐R, as mortality caused by pyriproxyfen did not increase over time in unselected hybrid strains and fitness traits were similar in unselected and selected hybrid strains. Using a new method to examine the inheritance of resistance, based on data from fitness cost experiments, it was estimated that pyriproxyfen resistance is controlled by two loci in the QC02‐R strain. CONCLUSION: The lack of fitness costs associated with pyriproxyfen resistance could promote the evolution of resistance in field populations with similar traits to QC02‐R. Copyright © 2008 Society of Chemical Industry     

Effects of a juvenile hormone analog,pyriproxyfen, on Thrips tabaci (Thysanoptera: Thripidae)

Effects of a juvenile hormone analog, pyriproxyfen, on various developmental stadia of the onion thrips, Thrips tabaci Lindeman, were determined on cabbage leaves in the laboratory. Pyriproxyfen was applied at 0.064 or 0.128 g AI liter(-1) on leaves (residual contact-ingestion), thrips (direct contact) and leaf-thrips (residue contact-ingestion-direct contact). Pyriproxyfen did not have any significant lethal effects on thrips pupae in any treatment. Lethal effects on thrips larvae varied depending on application method and dosage. In the leaf and the leaf-thrips treatments, few larvae and pre-pupae molted to the next stage, and none developed to adults. In contrast, in the thrips-only treatment, pyriproxyfen did not show any significant lethal effects. The developmental times of larvae and pre-pupae were prolonged when larvae were treated with pyriproxyfen, and those of pre-pupae and pupae were shortened when pre-pupae and pupae were treated. The longevity and survival rates of thrips adults were generally shorter when they contacted and ingested pyriproxyfen-treated leaves than those in water control. Significantly fewer progeny (0.22-1.15 larvae per female) were produced by females that had fed on and been in contact with the pyriproxyfen-treated leaves than by those in the water control (11.94 larvae per female). However, the number of progeny produced by the thrips females increased significantly (3.32-7.28 larvae per female) when the females were transferred to untreated leaves after feeding on treated leaves for 5 days; the daily larval hatching pattern was similar to those in water control, indicating that female adults were able to produce viable eggs when untreated food was offered.     

不同杀虫剂对烟蓟马的室内毒力与田间防效

烟蓟马是一种世界性害虫,为筛选出高效低毒的药剂,采用叶管药膜法测定了不同药剂对烟蓟马的室内毒力,并开展了田间防效试验。室内毒力测定结果表明,对成虫活性最高的药剂是阿维菌素、乙基多杀菌素和虫螨腈,其LC₅₀均小于1 mg/L;多杀霉素的毒力也较高,其LC₅₀为2.11 mg/L;吡丙醚对2龄若虫表现较高毒力。田间试验结果表明,2.5%高效氯氟氰菊酯SC、10%虫螨腈SC和60 g/L乙基多杀菌素SC对烟蓟马药后3~14 d的防效均达90%以上,除100 g/L吡丙醚SC外,其他药剂药后14 d的防效均达80%以上。2.5%高效氯氟氰菊酯SC、10%虫螨腈SC和60 g/L乙基多杀菌素SC可作为防治烟蓟马的首选药剂,并交替使用其他药剂。     

Q型烟粉虱细胞色素P450 CYP6DV5基因克隆及其在烟粉虱对噻虫嗪抗性中的作用

烟粉虱Bemisia tabaci 已严重危害农作物的正常生长,而新烟碱类杀虫剂噻虫嗪已被广泛用于烟粉虱的防治,但由于常年应用,致使烟粉虱对噻虫嗪产生了严重的抗性,而目前其抗药性分子机制尚不明确。本研究通过荧光定量PCR比较分析烟粉虱噻虫嗪抗性及敏感种群,发现细胞色素P450基因CYP6DV5在噻虫嗪抗性品系中的表达量为敏感品系的2.95倍,依据基因组数据库克隆该基因的全长序列,序列分析结果表明, 该基因具有细胞色素P450基因的保守结构域,属于典型的昆虫P450基因。进一步分析其在不同发育阶段和部位中的表达量,发现细胞色素P450基因CYP6DV5在烟粉虱成虫阶段和头部表达丰富,同时噻虫嗪能够显著诱导该基因的表达。通过RNA干扰试验,发现敲低CYP6DV5基因表达能够显著提高烟粉虱对噻虫嗪的敏感性。结果表明,CYP6DV5基因参与了Q型烟粉虱对噻虫嗪抗性的形成。研究结果将有助于揭示烟粉虱对噻虫嗪的抗性形成机制,并为烟粉虱的综合治理提供理论基础。     

烟粉虱细胞色素CYP6EM1基因的克隆及对吡虫啉抗性的作用

烟粉虱是一种世界性农业害虫,其防治手段以化学防治为主,新烟碱类杀虫剂吡虫啉常年用于防治烟粉虱,田间烟粉虱已经形成严重的抗药性。本研究通过分析烟粉虱吡虫啉抗性和敏感种群,发现细胞色素CYP6EM1基因在吡虫啉抗性品系中上调了4.7倍,进而克隆了其全长基因,进行了荧光定量PCR分析,发现该基因在吡虫啉抗性烟粉虱3龄若虫期和雄虫成虫期过量表达,并且在抗性成虫胸部和腹部过量表达。最后通过RNA干扰的方法使成虫的CYP6EM1基因表达量下降了54.8%,之后发现当烟粉虱暴露于吡虫啉时死亡率显著升高了39.65%,这表明CYP6EM1与烟粉虱对吡虫啉抗性的形成相关。研究结果对于揭示烟粉虱对吡虫啉产生抗性的机制有帮助,也为烟粉虱抗性水平田间监测及烟粉虱综合治理提供理论依据。     

烯啶虫胺对烟粉虱的使用技术及抗性风险评估研究

采用室内生物活性测定法系统测定了烯啶虫胺对烟粉虱不同虫态的毒力、成虫持效性、抗性风险评估和不同施药方法田间药效试验。结果表明,烯啶虫胺对烟粉虱低龄若虫和高龄若虫均表现出较高毒力,对成虫也有一定毒力,而对卵效果较差。烯啶虫胺水剂100 mg/L处理时对烟粉虱成虫1～15 d的校正死亡率在80.18%～92.13%之间,随着时间的延长,烯啶虫胺对烟粉虱的防效降低。烯啶虫胺喷雾和灌根方法效果较好,从速效性来说,喷雾好于灌根,从持效性来说,灌根优于喷雾,两种方法均显著高于单叶施药和涂茎法。经过8代6次选育,烟粉虱对烯啶虫胺抗性发展缓慢,与选育前相比敏感性降低2.653倍,烟粉虱对烯啶虫胺的抗性现实遗传力为0.102 5,在50%～90%的筛选压力下,要获得10倍抗性,需要9～21代,表明烟粉虱对烯啶虫胺有产生抗性的风险。     

Q型烟粉虱对20个烟草品种的选择性

为了明确不同烟草品种对Q型烟粉虱的抗性及其与叶背茸毛密度的相关性,研究了Q型烟粉虱对20个烟草品种的选择性及其生长发育和存活情况,并分析了烟草抗虫性与叶背茸毛密度的关系。结果表明,Q型烟粉虱成虫对烟草品种的选择性、产卵趋性及卵-成虫的存活率在不同烟草品种间差异显著。在20个供试烟草品种中,抗虫性较弱的品种有‘闽烟9号’、‘闽烟57号’;抗虫性较强的品种有‘云烟97’、‘V2’、‘云烟100’、‘长脖黄’,这4个品种在生产上可优先安排种植。烟草叶背茸毛密度与成虫量和着卵量均呈极显著正相关,即烟草叶背茸毛密度越高,烟草抗虫性越弱。因此,选育茸毛较少的烟草品种,可以提高烟草对Q型烟粉虱的抗性。     

Temporal synergism by microencapsulation of piperonyl butoxide and alpha-cypermethrin overcomes insecticide resistance in crop pests

A microencapsulated formulation that gives a burst release of piperonyl butoxide (PBO) several hours before a burst release of a conventional pyrethroid can effectively overcome metabolic resistance in Bemisia tabaci Gennadius, Helicoverpa armigera (Hübner), Aphis gossypii Glover and Myzus persicae Sulzer. This increase in efficacy against resistant pests was reflected in a field trial against B. tabaci on cotton, eliminating the need for two treatments. The ratio between the active insecticide and the synergist was found to be crucial in reducing resistance factors.     

杂草对9类常用不同作用机制除草剂的非靶标抗性机制研究进展

除草剂的应用为农业生产带来便利, 但长期、单一使用某一种或相同机制的除草剂也引发了杂草对除草剂的抗性问题。抗性杂草种类逐渐增加, 抗性形成机制复杂, 导致农田杂草的治理难度增加。杂草对除草剂的抗性机制主要分为两种, 一种是除草剂靶标位点基因的突变或过量表达导致的靶标抗性, 另一种是杂草对除草剂吸收、转运、固存和代谢等一个或多个生理过程发生变化导致的非靶标抗性。本文综述了杂草对9类不同作用方式除草剂的非靶标抗性机制的生理、生化和分子基础的研究进展, 以期为抗性杂草综合治理提供参考。     

近10年我国烟粉虱发生为害及防治研究进展

烟粉虱是我国重要农业害虫,近10年来我国烟粉虱发生为害呈现以下特点:烟粉虱的优势生物型/隐种由B型更替为Q型;传播植物病毒(如黄化曲叶病毒、番茄褪绿病毒)成为了烟粉虱重要的为害方式;烟粉虱抗药性问题逐渐突出;化学农药尤其新烟碱类杀虫剂的广泛使用是Q型烟粉虱取代B型烟粉虱的关键因素。烟粉虱的综合防控措施日益完善,抗药性治理与非化学防控措施受到重视,但是依靠农药的现状并未完全改变。本文综述了近10年来我国烟粉虱的发生为害及防治方面的概况,探讨了今后烟粉虱防控方面的研究内容。     

Effect of pyriproxyfen,a juvenile hormone mimic,on egg hatch,nymph development,adult emergence and reproduction of the Asian citrus psyllid,Diaphorina citri Kuwayama

BACKGROUND: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is a vector of bacteria presumably responsible for huanglongbing (HLB) disease in citrus. In this laboratory study, an investigation was made of the activity of pyriproxyfen, a juvenile hormone mimic, on ACP eggs, nymphs and adults to evaluate its potential as a biorational insecticide for inclusion in an integrated pest management (IPM) program for ACP. RESULTS: Irrespective of egg age, timing or method of treatment, a significantly lower percentage of eggs (5–29%) hatched after exposure to 64 and 128 µg mL^?1 of pyriproxyfen. Only 0–36% of early instars (first, second and third) and 25–74% of late instars (fourth and fifth) survived to adults following exposure to 16, 32 and 64 µg mL^?1 of pyriproxyfen. However, 15–20% of adults that emerged following treatment as late instars exhibited morphological abnormalities. Furthermore, pyriproxyfen adversely affected reproduction (fecundity and fertility) of adults that emerged from treated fifth instars or that were treated topically with 0.04 µg as adults. CONCLUSIONS: Application of pyriproxyfen at 64 µg mL^?1 resulted in greater inhibition of egg hatch and suppression of adult emergence compared with lower rates. Pyriproxyfen also markedly reduced female fecundity and egg viability for adults that were exposed either as fifth instars or as newly emerged adults. The ovicidal, larvicidal and reproductive effects against ACP suggest that pyriproxyfen is suitable for integration into an IPM program for ACP. Copyright © 2009 Society of Chemical Industry     

Toxicological and mechanistic studies on neonicotinoid cross resistance in Q-type Bemisia tabaci (Hemiptera: Aleyrodidae)

The tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) is a serious pest in numerous cropping systems and has developed a high degree of resistance against several chemical classes of insecticides. One of the latest group of insecticides introduced to the market were the neonicotinoids (chloronicotinyls), acting agonistically on insect nicotinic acetylcholine receptors. Resistance to neonicotinoid insecticides has recently been shown to occur, especially in Q-type B tabaci in some places in Almeria, Spain, whereas control of B-type B tabaci in many other intense cropping systems worldwide has remained on high levels. Our study revealed that neonicotinoid-resistant Q-type strains from Almeria were often more than 100-fold less susceptible to thiamethoxam, acetamiprid and imidacloprid when tested in discontinuous systemic laboratory bioassays. The resistance factors were generally 2- to 3-fold lower in leaf-dip bioassays. In addition to the Spanish strains, we obtained two other highly neonicotinoid-cross-resistant B tabaci greenhouse populations, one from Italy (December 1999) and one from Germany (June 2001). A molecular diagnostic analysis revealed that both strains also belong to the (Spanish) subtype Q of the B tabaci species complex. The resistance levels of Q-type whitefly strains derived from Almeria greenhouses in 1999 remained stable for at least two years, even when maintained in the laboratory without any selection pressure. The biochemical mechanisms conferring resistance to neonicotinoids have not yet been elucidated in detail, but synergist studies suggested a possible involvement of microsomal monooxygenases. Furthermore, we checked two Almerian strains of B tabaci isolated in 1998 and 1999 and demonstrated that neonicotinoid resistance is not due to an altered [3H]imidacloprid binding site of nicotinic acetylcholine receptors.     

Insecticide resistance in Bemisia tabaci (Homoptera: Aleyrodidae) populations from Crete

The resistance levels to alpha-cypermethrin, bifenthrin, pirimiphos-methyl, endosulfan and imidacloprid were determined in Bemisia tabaci (Gennadius) from Crete. Five B tabaci populations collected from greenhouse and outdoor crops were bioassayed and compared with a reference susceptible strain. Bemisia tabaci collected in a floriculture greenhouse exhibited the highest resistance against all insecticides: at LC50, resistance factors were 23-fold for bifenthrin, 80-fold for alpha-cypermethrin, 18-fold for pirimiphos-methyl, 58-fold for endosulfan and 730-fold for imidacloprid. A population collected on outdoor melons was more susceptible than the reference strain against all insecticides tested, suggesting the occurrence of local highly susceptible B tabaci populations in 'refugia'. In pairwise comparisons of resistance levels, correlation was observed between the LC50 values of the pyrethroid insecticides bifenthrin and alpha-cypermethrin.     

Age-specific expression of resistance to a neonicotinoid insecticide in the whitefly Bemisia tabaci

Neonicotinoid insecticides retain a crucial role within many chemical and integrated control strategies for the tobacco whitefly, Bemisia tabaci Gennadius, in spite of the establishment of potent and widespread resistance in many areas. Metabolic resistance mechanisms mediated by overexpression of P450-dependent monooxygenases have been implicated in neonicotinoid resistance in the two most prevalent B. tabaci biotypes. Further characterisation of resistance to the neonicotinoid imidacloprid in populations of both these B- and Q-types is reported.Expression of resistance to imidacloprid was age specific in B- and Q-type strains of B. tabaci. The highest observed resistance ratio at LC(50) expressed in prepupal nymphs was 13, compared with at least 580 in their adult counterparts. For all strains, resistance expressed in immatures was not sufficiently potent to compromise recommended imidacloprid application rates.Targeting neonicotinoids towards immature life stages of B. tabaci may circumvent the protection conferred by current mechanisms of resistance, simultaneously reducing the selection pressures imposed. However, such tactics may enhance the expression of existing resistance mechanisms in immatures, or promote the establishment of novel ones expressed in all life stages.