Stability of field-selected resistance to insecticides in Plutella xylostella (Lep., Plutellidae) from Pakistan

Abstract:  To investigate fluctuation in susceptibility to insecticides, natural populations of Plutella xylostella were collected from the same field in the region of Multan, Pakistan, in late summer, mid-winter and early spring. After bulking up for a generation in the laboratory, the populations were examined against pyrethroids and organophosphates as well as newer insecticides (spinosad, indoxacarb and emamectin). Each population showed a broad range of variation in susceptibility to all chemicals. Comparison between populations collected in different times of years in 2003 and 2004 showed variation in susceptibility to organophosphates and pyrethroids. In winter, susceptibility to organophosphates increased, whereas it decreased in relation to pyrethroids. However, susceptibility to the newer insecticides was unchanged within the season. The results suggest that the fluctuation observed in susceptibility could be either associated with fitness costs of organophosphate and pyrethroids or cessation of insecticides. These results might have important implications in resistance management. We propose a strategy for application of insecticides in relation to P. xylostella management in Pakistan.     

小菜蛾幼虫对不同寄主的取食嗜好性及其适宜性

对不同寄主种类、不同寄主形态和不同寄主饲喂的小菜蛾(Plutella xylostella)幼虫之间的取食嗜好性比较试验表明,小菜蛾幼虫优先取食大白菜、萝卜或菜心幼苗,其次为油菜和甘蓝幼苗,在大白菜与油菜幼苗之间的取食选择比例是93.33%和6.67％;在甘蓝与菜心幼苗之间的取食选择比例是16.67%和83.33%.小菜蛾幼虫的取食嗜好性受饲喂寄主种类的影响,偏食大白菜或菜心幼苗.小菜蛾幼虫选择寄主取食的次序与寄主体内可溶性糖或淀粉含量没有明显关系,但与两者的相对量呈一定的负相关.取食大白菜或菜心幼苗的小菜蛾生长良好,单头取食达0.583～0.637 cm², 单头体重达2.07～2.18 mg, 与取食甘蓝或油菜幼苗的幼虫在取食量、个体发育方面有明显差异.小菜蛾幼虫也喜好取食已经被虫危害过的幼苗.     

Evaluating trap crops for diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Potential trap crops for the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were evaluated through a series of ovipositional preference and larval survival experiments in outdoor screenhouses in 2002 and 2003. Hosts examined as trap crops were glossy and waxy collards, Brassica oleracea L. variety acephala; Indian mustard, Brassica juncea (L.) Czern; and yellow rocket, Barbarea vulgaris (R. Br.) variety arcuata. More eggs were laid on the potential trap crops, with the exception of waxy collards, than on cabbage. When P. xylostella was offered multiple hosts at the same time, numbers of eggs laid on glossy collards, Indian mustard, and yellow rocket were 3, 18, and 12 times greater than on cabbage, respectively. Similarly, when P. xylostella was offered a single trap crop host and cabbage, numbers of eggs laid on glossy collards, Indian mustard, and yellow rocket were 300, 19, and 110 times greater than on cabbage, respectively. Our studies suggest differences in oviposition between the potential trap crops and cabbage were likely due to host volatiles, leaf morphology and color, or a combination of these factors, rather than to total leaf areas, leaf shape, or plant architecture. Two-choice tests with a Y-tube olfactometer indicated that plant volatiles were major factors in P. xylostella host preference. The percentage larval survival from egg to pupation was 22.2% on cabbage, 18.9% on waxy collards, and 24.4% on Indian mustard, whereas survival was significantly lower on glossy collards (6.7%) and yellow rocket (0%). Based on our tests, it seems that yellow rocket may be the best candidate for use as a trap crop for P. xylostella because it is highly attractive for oviposition, but larvae do not survive on it.     

Genetic, biochemical, and physiological characterization of spinosad resistance in Plutella xylostella (Lepidoptera: Plutellidae)

Bioassays (at generation G2) with a newly collected field population (designated MN) of Plutella xylostella (L.) (Lepidoptera: Plutellidae) from Multan, Pakistan, indicated resistance to spinosad, indoxacarb, deltamethrin, abamectin, and acetamiprid. At G2 the field-derived population was divided into two subpopulations, one was selected (G2 to G11) with spinosad (Spino-SEL), whereas the second was left unselected (UNSEL). A significant reduction in the resistance ratio for each compound was observed in UNSEL at G12, indicating that the observed resistance to each insecticide was unstable. For Spino-SEL, bioassays at G12 found that selection with spinosad gave a resistance ratio of 283 compared with MN at G2. The resistance to indoxacarb and acetamiprid in the Spino-SEL population increased to 13- and 67-fold, respectively, compared with MN at G2. The toxicity of deltamethrin to Spino-SEL was similar to its toxicity to the MN population at G2. This suggests that spinosad selection maintained the otherwise unstable resistance to the compound. In contrast, resistance to abamectin decreased significantly from G2 to G12 in Spino-SEL. Logit regression analysis of F1 reciprocal crosses between Spino-SEL and the susceptible Lab-UK indicated that resistance to spinosad was inherited as an autosomal, incompletely recessive trait. The spinosad resistance allele significantly delays the developmental time, reduced pupal weight, number of eggs laid, and number of eggs hatched compared with Lab-UK. Further analysis suggests Spino-SEL exhibited a significantly lower intrinsic rate of population increase (r(m)) to all other populations tested.     

Resistance of some cultivated Brassicaceae to infestations by Plutella xylostella (Lepidoptera: Plutellidae)

Selecting insect-resistant plant varieties is a key component of integrated management programs of oligophagous pests such as diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), but rigorous research on important life history parameters of P. xylostella in relation to host plant resistance is rare. We evaluated six conventional brassicaceous species, namely, Brassica napus L. 'Q2', B. rapa L., B. juncea (L.) Czern., B. carinata L., B. oleracea L., and Sinapis alba L., and two herbicide-tolerant cultivars, namely, B. napus 'Liberty' and B. napus 'Conquest' for their resistance against P. xylostella. Brassicaceae species and cultivars varied considerably in their susceptibilities as hosts for P. xylostella. Sinapis alba and B. rapa plants were highly preferred by ovipositing females and trichome density on adaxial and abaxial leaf surfaces had nonsignificant effects on P. xylostella oviposition. Larval survival was similar on the genotypes we tested, but host plants significantly affected larval and pupal developmental time, herbivory, pupal weight, silk weight, adult body weight, forewing area and longevity (without food) of both male and female P. xylostella. Larval and pupal development of females was fastest on B. juncea and S. alba, respectively. Specimens reared on B. napus Liberty and B. oleracea, respectively, produced the lightest female and male pupae. Defoliation by both female and male larvae was highest on B. rapa, whereas least herbivory occurred on S. alba. Females reared on S. alba were heavier and lived longer in the absence of food than their counterparts raised on other tested host plants. Brassica oleracea could not compensate for larval feeding to the level of the other species we evaluated. B. napus Conquest, B. napus Q2, B. carinata, B. rapa, and S. alba produced, respectively, 1.6-, 1.8-, 1.8-, 3.9-, and 5.5-fold heavier root systems when infested than their uninfested counterparts, suggesting that these species were better able to tolerate P. xylostella infestations.     

Isolation and characterization of Pseudomonas cedrina infecting Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth, Plutella xylostella, is one of the most destructive pests worldwide and its management relies exclusively on frequent application of chemical insecticides. Resistance to common insecticides is now widespread, and novel classes of insecticides are needed. Entomopathogenic bacteria and their related products play an important role in the management of this pest. In the present work, one bacterial strain was separated from infected pupae of P. xylostella collected from field and its pathogenicity was evaluated. On the basis of the 16S ribosomal RNA sequencing, BLASTN, and phylogenetic analysis, this bacterial isolate was identified as Pseudomonas cedrina. Oral administration of P. cedrina at levels above 10,000 CFU/ml gave significant mortality to P. xylostella larvae. The pathogenicity was also observed by reduced longevity and fecundity in adult females. However, when live bacterial cells were removed, the cultured broth lost any pathogenicity. In response to the bacterial infection, P. xylostella expressed antimicrobial and stress‐associated genes. A mixture treatment of P. cedrina and Bacillus thuringiensis showed an additive effect on larval mortality of P. xylostella. These results indicated that P. cedrina is an opportunistic entomopathogen without secretion of toxins. Furthermore, the additive effect of P. cedrina and B. thuringiensis provide a new insight to develop new strategy for controlling P. xylostella.     

Oviposition by Plutella xylostella (Lepidoptera: Plutellidae) and effects of phylloplane waxiness

Three approaches were used to investigate effects of host plant epicuticular waxes on oviposition site selection by Plutella xylostella (L.). In the first approach, oviposition on canola (Brassica napus L.) that had epicuticular wax reduced by application of a carbamate herbicide (S-ethyl dipropylthiocarbamate) was compared with oviposition on untreated control plants. A second approach compared oviposition on sibling strains of B. napus with different wax blooms (glossy and waxy), and a third approach compared oviposition by P. xylostella on parafilm that had been applied to glossy and waxy B. napus strains for transfer of leaf components. Significantly more eggs were deposited on herbicide-treated plants (with reduced epicuticular wax) than on untreated controls. Similarly, more eggs were deposited on glossy than on waxy sibling strains of B. napus. In parafilm assays significantly more eggs were deposited on treated than on untreated parafilm. Several mechanisms could explain the differences in attractiveness of surfaces with varying wax content as oviposition sites for P. xylostella, including visual, chemical, and tactile differences between substrates. These mechanisms are discussed.     

茚虫威和高效氯氰菊酯对小菜蛾的亚致死效应

【目的】通过研究茚虫威和高效氯氰菊酯两种杀虫剂对小菜蛾Plutella xylostella (L.)的亚致死效应, 进一步了解农药的杀虫机制, 同时为合理使用农药、 减少农药给环境和农业生产带来的一系列不良影响提供理论依据。【方法】浸叶法测定茚虫威和高效氯氰菊酯对小菜蛾2龄幼虫的毒力; 选择茚虫威的3个实验浓度（TI-LC₁₅, TI-LC₃₀和TI-LC₅₀）和高效氯氰菊酯的3个实验浓度（TB-LC₁₅, TB-LC₃₀和TB-LC₅₀）分别处理小菜蛾2龄幼虫48 h, 记录各虫态存活率和发育历期, 3龄、 4龄幼虫及蛹的重量, 并记录单雌产卵量和成虫寿命; 应用特征年龄 龄期及两性生命表方法, 研究不同处理组小菜蛾后代的生长发育、 存活率以及种群增长。【结果】TI-LC₃₀, TI-LC₅₀, TB-LC₁₅, TB-LC₃₀和TB-LC₅₀处理组各虫态发育历期比对照组显著延长（P<0.05）, 3龄、 4龄幼虫和蛹的重量以及单雌产卵量均显著低于对照组（P<0.05）, 但TI-LC₁₅组小菜蛾3龄和4龄幼虫发育历期均显著低于对照组（P<0.05）。TI-LC₃₀, TI-LC₅₀, TB-LC₃₀和TB LC50组小菜蛾后代的总产卵期显著短于相应对照组（P<0.05）, 产卵量也都显著降低（P<0.05）; TI和TB实验组小菜蛾后代种群内禀增长率r_m、 周限增长率λ、 净生殖率R₀以及总生殖率GRR都比对照显著降低（P<0.05）。【结论】低剂量的茚虫威和高效氯氰菊酯能显著抑制处理当代小菜蛾的生长发育和生殖, 并对其下一代的生长发育及种群增长也有明显的抑制。     

The effects of local selection versus dispersal on insecticide resistance patterns: longitudinal evidence from diamondback moth (Plutella xylostella (Lepidoptera: Plutellidae)) in Australia evolving resistance to pyrethroids

When strong directional selection acts on a trait, the spatial distribution of phenotypes may reflect effects of selection, as well as the spread of favoured genotypes by gene flow. Here we investigate the relative impact of these factors by assessing resistance to synthetic pyrethroids in a 12-year study of diamondback moth, Plutella xylostella, from southern Australia. We estimated resistance levels in populations from brassicaceous weeds, canola, forage crops and vegetables. Differences in resistance among local populations sampled repeatedly were stable over several years. Levels were lowest in samples from weeds and highest in vegetables. Resistance in canola samples increased over time as insecticide use increased. There was no evidence that selection in one area influenced resistance in adjacent areas. Microsatellite variation from 13 populations showed a low level of genetic variation among populations, with an AMOVA indicating that population only accounted for 0.25% of the molecular variation. This compared to an estimate of 13.8% of variation accounted for by the resistance trait. Results suggest that local selection rather than gene flow of resistance alleles dictated variation in resistance across populations. Therefore, regional resistance management strategies may not limit resistance evolution.     

不同地理种群小菜蛾的遗传多样性分析

采用水平切片淀粉凝胶电泳方法,分析了北京、河北、云南和武汉4个不同地理种群的小菜蛾的等位酶,得到了3个酶系统（甘油醛磷酸脱氢酶（GPD）、苹果酸酶（ME）和苹果酸脱氢酶（MDH-1,MDH-2和MDH-3）5个基因位点的资料。用Biosys2.0软件计算了不同地理种群的遗传变异指标（N、A、P、H0和He）,结果表明小菜蛾各种群内的基因多样性大于各种种群间的基因多样性（约15倍）,武汉种群小菜蛾的遗传性最大。并计算了遗传距离D和相似性系数,并由此得出聚类图,分析了小菜蛾不同地理种群间的遗传关系。     

Functional and genetic characteristics of Chlorantraniliprole resistance in the diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth (Plutella xylostella) is a globally distributed and important economic pest, and it has developed resistance to all conventional insecticide classes used in the field. Chlorantraniliprole is a new chemical class of insecticide that acts as a conformation‐sensitive activator of the insect ryanodine receptor (RyR). In the present study, a field strain (16.3‐fold resistance to chlorantraniliprole) was collected in Korea and lab‐selected with chlorantraniliprole for more than one year. The resulting strain presented 2,157‐fold resistance to chlorantraniliprole. A point mutation (G4946E) in the RyR gene was observed at a high frequency in the resistant strain. Enzyme assays indicated that glutathione S‐transferase (GST) and P450 activity in the resistant strain were 2.4‐ and 1.96‐times higher than that of the susceptible strain, respectively. The expression of the RyR, GST (sigma, omega, and zeta) and CYP321E1 gene was higher in the resistant strain than in the susceptible strain. The F₁ progeny resulting from reciprocal crosses did not reveal maternal effects or a diamide‐susceptible phenotype, which suggests an autosomal nearly recessive mode of inheritance. In addition, we surveyed the susceptibility to 13 insecticides (3 diamides, 2 synthetic pyrethroids, 2 spinosyns, 1 organophosphate, 1 oxadiazine, 1 avermectin, and 3 others) in the chlorantraniliprole‐resistant strain. The resistant strain exhibited high cross‐resistance to flubendiamide (5,910 fold) and showed no cross‐resistance to spinetoram, spinosad, indoxacarb, and metaflumizone. These results can serve as an important basis for guiding the use of insecticides in the field.     

小菜蛾抑制性谷氨酸受体的RNA干扰

谷氨酸门控的氯离子通道（glutamate-gated chloride channels, GluCls）或抑制性谷氨酸受体（inhibitory glutamate receptor, IGluR）是阿维菌素类药剂（avermectins）主要的作用靶标, 目前人们对于昆虫的IGluR知之甚少。本实验采用RNA干扰（RNAi）技术对小菜蛾Plutella xylostella IGluR的功能进行了初步研究。结果表明： 小菜蛾2龄和3龄幼虫中双链RNA（dsRNA）的最佳注射量分别为50.6 nL和71.3 nL。实时荧光定量（quantitative real-time PCR, qRT-PCR）检测结果表明, 2龄和3龄幼虫在注射dsRNA 36 h和24 h后IGluR基因的转录后水平分别下降了32.67%和49.30%。幼虫发生RNA干扰后对阿维菌素的敏感性结果显示, 注射了IGluR dsRNA的幼虫死亡率显著低于对照。结果说明, 小菜蛾IGluR是阿维菌素的潜在靶标之一, 为进一步阐明小菜蛾对阿维菌素靶标抗性机理奠定了基础。     

Exploring Valid Reference Genes for Quantitative Real-time PCR Analysis in Plutella xylostella (Lepidoptera: Plutellidae)

Abstract: Quantitative real-time PCR (qRT-PCR), a primary tool in gene expression analysis, requires an appropriate normalization strategy to control for variation among samples. The best option is to compare the mRNA level of a target gene with that of reference gene(s) whose expression level is stable across various experimental conditions. In this study, expression profiles of eight candidate reference genes from the diamondback moth, Plutella xylostella, were evaluated under diverse experimental conditions. RefFinder, a web-based analysis tool, integrates four major computational programs including geNorm, Normfinder, BestKeeper, and the comparative ΔCt method to comprehensively rank the tested candidate genes. Elongation factor 1 (EF1) was the most suited reference gene for the biotic factors (development stage, tissue, and strain). In contrast, although appropriate reference gene(s) do exist for several abiotic factors (temperature, photoperiod, insecticide, and mechanical injury), we were not able to identify a single universal reference gene. Nevertheless, a suite of candidate reference genes were specifically recommended for selected experimental conditions. Our finding is the first step toward establishing a standardized qRT-PCR analysis of this agriculturally important insect pest.     

Effects of temperature and humidity on emergence dynamics of Plutella xylostella (Lepidoptera: Plutellidae)

The effects of temperature and humidity on the emergence patterns of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were studied at four temperatures (20, 25, 28, and 33 degrees C),three relative humidities (50, 70, and 90%) and a photoperiod of 14:10 (L:D) h. Both sexes emerged primarily in the late afternoon to early morning, and the peaks of emergence varied depending on temperature and humidity. Females emerged significantly earlier than males. Incubation at 33 degrees C and 90% RH had a significant effect on the emergence rate, but no significant interaction was found between temperature and humidity. Emergence duration was 25.3 h for both sexes at 90% RH, with emergence duration at 33 degrees C lower than the other treatments. The sex ratios of diamondback moth under different temperature and humidity treatments were approximately 1:1, and there were no significant effects of temperature and humidity or interactions between these two factors.     

Functional response and predation of Nabis kinbergii （Hemiptera. Nabidae） to Plutella xylostella （Lepidoptera. Plutellidae）

The functional response of adult Nabis kinbergii （Hemiptera： Nabidae） to density of diamondback moth Plutella xylostella （Lepidoptera： Plutellidae） was investigated under laboratory conditions. Holling＇ s （1959） type Ⅱ model was found to be a good fit for the observed functional response of this predator. The numbers of P. xylostella consumed increased with temperature from 15℃ to 35℃. The maximum number of prey killed was observed at 35℃, with average of 10.3 and 8.3 forth instar larvae consumed by adult females and males of N. kinbergii, respectively. The predation of N. kinbergii on P. xylostella increased with successive immature stages. The number of prey consumed by predators decreased as the body size of prey increased. An average of 131 eggs or 95 larvae of P. xylostella were killed by a single of female adult in 24 hours at 24＂C. The pupae of P. xylostella were observed to be eaten by fifth instar nymphs and adults N. kinbergiiin numbers of less than an average of 0.7 pupae per predator in 24 hours at 24＂C. Predation preference by N. kinbergii was also investigated. The number of P. xylostella and Myzus persicae killed by female N. kinbergii was not significantly different, but males killed significantly more P. xylostella than M. persicae. Both eggs and larvae of P. xylosteUa were killed in significantly greater number than those of Pieris rapae in the same feeding arena.     

Management of diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae) by mating disruption

Abstract Field trials were conducted in China in 2008 and 2009 to evaluate the efficacy of mating disruption (MD) on diamondback moth, Plutella xylostella, in cabbage, Brassica oleracea var. capitata. Effectiveness was positively correlated with the MD dispenser density in the field. A density of 167 MD dispensers per ha produced an average population decrease of about 50% compared to the conventional‐practice field. Significant fewer males were captured in pheromone‐treated and conventional‐practice fields than in the blank control field, but the difference was not significant between the pheromone‐treated and conventional‐practice fields. In addition, fewer eggs and larvae were observed in pheromone‐treated fields. Our results suggest mating disruption coupled with minimal insecticidal supplements is a promising solution for resistance management and control of diamondback moth infestation.     

Detection of insecticide resistance in Plutella xylostella (L.) (Lepidoptera: Plutellidae) populations in South Australian crucifer crops

In response to reports of failures of sprays to control Plutella xylostella infestations in vegetable-growing areas around Adelaide in 1991, the extent of resistance to six insecticides in several South Australian populations of P. xylostella was determined. Populations sampled from vegetable crops in the Adelaide region were five- to 200-fold resistant to organophosphates (chlorpyrifos, methamidophos and mevinphos), eight- to 400-fold resistant to pyrethroids (esfenvalerate and permethrin) and six-fold resistant to the carbamate methomyl compared with a susceptible strain. Mevinphos and esfenvalerate were the most effective of the tested insecticides. These, together with Bacillus thuringiensis products, have continued until 1998 to be used almost exclusively for the control of P. xylostella in South Australian vegetable crops in the absence of any resistance management strategy.     

羧酸酯酶介导的小菜蛾对氟虫腈的抗性

【目的】羧酸酯酶（carboxylesterases, CarEs）是昆虫重要的解毒代谢酶之一,可以介导靶标昆虫对多种杀虫剂的代谢抗性。本研究检测了羧酸酯酶对小菜蛾Plutella xylostella 抗药性的介导功能,旨在阐明羧酸酯酶在小菜蛾代谢解毒中的生理生化和分子机理。【方法】采用点滴法测定氟虫腈对小菜蛾敏感种群和抗氟虫腈种群的毒力,以及羧酸酯酶抑制剂磷酸三苯酯（triphenyl phosphate, TPP）对氟虫腈的增效作用;以LC₃₀和LC₅₀浓度的氟虫腈处理抗性小菜蛾,测定药剂处理后CarEs酶活性的变化;利用qRT-PCR技术分析Pxae22和Pxae31两个基因在小菜蛾不同发育阶段、组织和种群的表达模式;利用dsRNA干扰Pxae22和Pxae31后观察基因的表达变化和小菜蛾3龄幼虫对药剂敏感性的变化。【结果】TPP可以削弱小菜蛾3龄幼虫对氟虫腈的抗性,增效倍数约为6倍;使用较低剂量（LC₃₀和LC₅₀）氟虫腈处理小菜蛾3龄幼虫后,处理组CarEs比活力明显高于对照,提示氟虫腈对小菜蛾CarEs活性具有诱导作用。对羧酸酯酶基因Pxae22和Pxae31在小菜蛾不同发育阶段、4龄幼虫不同组织和不同种群3龄幼虫中的表达模式分析发现,这两个基因在小菜蛾4龄幼虫中的表达量最高;在4龄幼虫中以中肠组织中的表达量较高,头、表皮、脂肪体中的表达量很低; 抗性种群中的表达量显著高于敏感种群。通过干扰 Pxae22和 Pxae31后的qRT-PCR验证,两个基因的表达量均显著降低,进一步的氟虫腈毒力测定发现,干扰P xae22和 Pxae31后的小菜蛾3龄幼虫对氟虫腈的敏感性分别增加了1.63倍和1.73倍。【结论】羧酸酯酶在小菜蛾对氟虫腈解毒代谢中具有重要作用;Pxae22和Pxae31是小菜蛾的两个抗性相关基因,其表达水平的变化直接影响小菜蛾对氟虫腈的敏感性。     

Behavioural responses of diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) to extracts derived from Melia azedarach and Azadirachta indica

The impact of three different doses of botanical insecticide derived from the syringa tree, Melia azedarach and the neem tree, Azadirachta indica was tested on the behaviour of the diamondback moth, Plutella xylostella (Linnaeus). Both botanical insecticides had a significant impact on larval behaviour. At higher doses the extracts showed feeding deterrent activity, with larvae preferring the untreated sides of cabbage leaves and consuming less of the treated half of cabbage leaves. The botanical insecticides had less of an effect on the oviposition behaviour of P. xylostella moths. In laboratory and glasshouse trials, significantly fewer eggs were oviposited on the plants that had been treated with syringa extracts. Therefore, the syringa extracts appear to have a repellent effect. In contrast, when exposed to the neem extracts the moths did not discriminate between control plants and treated plants. Behavioural observation indicated that, despite the lower number of eggs oviposited on cabbage treated with syringa extracts, the moths chose cabbage treated with the highest dose of syringa more often than they chose control cabbage plants. Similar observations were found in cabbage plants treated with neem, moths chose the medium dose more often than they chose the control. Oviposition and feeding deterrent properties are important factors in pest control, and results from this study indicate that botanical insecticides have the potential to be incorporated into control programmes for P. xylostella in South Africa.     

Bacillus thuringiensis isolates from northeastern Brazil and their activities against Plutella xylostella (Lepidoptera: Plutellidae) and Spodoptera frugiperda (Lepidoptera: Noctuidae)

Northeastern Brazil has been little explored in the search for Bacillus thuringiensis (Berliner) variants for the control of agricultural pests such as Plutella xylostella (L.) and Spodoptera frugiperda (J.E. Smith). The aim of this study was to isolate B. thuringiensis from soil and insect samples collected from the northeastern states and to evaluate their lethal and sublethal activities against the neonate larvae of P. xylostella and S. frugiperda. One hundred and four isolates were bioassayed and visualised for the presence of crystals. Bipyramidal crystals were present in 31% of the isolates. In pathogenicity tests, 13 and 19 isolates caused >30% mortality in P. xylostella and S. frugiperda, respectively. The Laboratory of Insect-Toxic Interactions (LIIT)-4311 isolate was the most toxic for P. xylostella, with toxicity similar to B. thuringiensis var. kurstaki (Dipel® WP) and B. thuringiensis var. aizawai (Xentari® WDG). For S. frugiperda, the LIIT-4311, LIIT-4306 and LIIT-4406 isolates were more active than B. thuringiensis var. aizawai. The LIIT-4311 and LIIT-4306 isolates caused high rates of larval growth inhibition in both P. xylostella and S. frugiperda. These results suggest a broad distribution of B. thuringiensis variants in areas of northeastern Brazil. Because LIIT-4306 and LIIT-4311 provided the highest levels of toxicity and larval growth inhibition for both P. xylostella and S. frugiperda, these isolates can be exploited to develop new technologies for pest management.