Phenology, damage and parasitoids of the apple leaf cutter Coenorhinus pauxillus (Germ.) (Col.: Attelabidae)

An outbreak on apple permitted a closer look at Coenorhinus pauxillus (Germar) (Col.: Attelabidae). The adult weevils emerge from mid-March onwards and attack the first unfolding leaves. Infested leaves drop when the larvae are in the 1^st or 2^nd instar, and it takes a further 4 weeks before the larvae are ready to pupate. Rearing of field-collected eggs and larvae is described. Leaf decomposition is an essential condition for pupation, as the fully-grown larvae do not leave their mine actively. Part of the population pupates more or less immediately and produces adult weevils in autumn. However, up to 70% of the weevils remain in prolonged diapause; their pupation does not take place before the summer of the following year. Damage by the weevil involves not only the loss of leaves of flower clusters and shoots, but also feeding damage to young fruits. Two parasitoids were found. Observations indicate that 3–4 subsequently more abundant generations of Anaphes brachygaster Debauche (Hym.: Mymaridae) develop in eggs of C. pauxillus. Probles brevicornisHorstmann (Hym.: Ichneumonidae, Tersilochinae) emerges in May and oviposits in young weevil larvae on the tree. The parasitoid does not develop into a pupa until its host starts pupating. The outbreak of apple leaf cutter did not decline over three years, but did not spread into adjacent plantings.     

Metabolic insecticide defenses in the boll weevil compared to those in a resistance-prone species

Activities of cytochrome P-450-dependent microsomal monooxygenases (PMSO) are up to 46-fold higher in insecticide-susceptible fifth instar tobacco budworm larvae than in adult boll weevils. Glutathione transferase and esterase activities are likewise higher in susceptible tobacco budworm larvae than in adult boll weevils, the life stages of the two species that are exposed to selection pressure from insecticide treatments. Good metabolic defenses may facilitate insecticide resistance development in the tobacco budworm. Differences in ecological, biological, and other biochemical factors, not quantified in this study, are also likely to contribute to the observed differences in resistance development in the two species. PSMO activities as well as glutathione transferase and esterase activities are 3- to 11-fold higher in boll weevil larvae than in adults. Exposure of the life stage with the weakest metabolic defenses to insecticide selection pressure in the boll weevil may contribute to its relative lack of resistance development.     

Systemic effects of thiamethoxam and chlorantraniliprole seed treatments on adult Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) in rice

BACKGROUND: Feeding assays using adult rice water weevils and foliage of plants treated as seeds with chlorantraniliprole and thiamethoxam at different rates were conducted to evaluate the systemic adulticidal and feeding effects. Dose–mortality relationships were determined for thiamethoxam seed treatments by combining leaf area lost due to feeding and insecticide residues analyzed by LC/MS/MS. Changes in adulticidal activity of thiamethoxam were also investigated by contrasting adult mortalities at the 5–6‐leaf and tillering stages of rice. RESULTS: Adult weevil mortalities and leaf consumption rates on foliage were affected in thiamethoxam but not in chlorantraniliprole treatments when rice was at the 6–7‐leaf stage. The LD₅₀ for weevils feeding on thiamethoxam‐treated rice at the 2–3‐leaf stage was 447 pg insecticide weevil^?1 (95% CL: 25–830 pg weevil^?1) but was lower (142 pg weevil^?1; 95% CL: 102–180 pg weevil^?1) in experiments with 3–4‐leaf‐stage plants. Mortalities on leaves from 5–6‐leaf‐stage plants were consistently higher than on leaves from tillering plants. Thiamethoxam residues measured by ELISA increased with seed treatment rate and differed between plant stages. CONCLUSION: The LD₅₀ values developed in this study are the first values for leaf‐feeding insects on foliage of plants treated as seeds with thiamethoxam. The attrition of adulticidal activity of thiamethoxam in foliage of older plants may help to explain the reduced effectiveness of seed treatments against rice water larvae that is seen at later stages of rice growth in field studies. The differential activity of these two seed treatments on adults suggests that adult mortality contributes to the field efficacy of thiamethoxam but not to that of chlorantraniliprole. Copyright © 2012 Society of Chemical Industry     

Impact of 2,4-D on Ceuthorhynchidius horridus (Coleoptera: Curculionidae) and their compatibility for integrated control of Carduus thistles

Acute and chronic effects of spring application of 2,4-D on adult C. horridus (Panzer) were examined by determining dose-mortality response and adult vitality. LC₅₀ values for males (70.2 kg/ha) and females (61.4 kg/ha) corresponded to 41.7 and 36.6 times, respectively, the recommended application rate of 1.68 kg/ha. Survival of weevils treated with 1.68 kg/ha was not different from untreated controls, but higher doses (16.8–147.8 kg/ha) caused significantly greater mortality. Adult vitality, measured by number of feeding marks per weevil and rate of weight change. was unaffected by the herbicide. When thistle infested fields were sprayed with 1.68 or 2.24 kg/ha of 2,4-D the host plants died, but the survival, reproduction, and population increase of C. horridus were not affected.     

寄主与粮粒对雅脊金小蜂寄生和发育的影响

从三级营养关系出发,研究了不同粮食（小麦和玉米）和寄主（米象和玉米象）对雅脊金小蜂发育和寄生的影响。结果表明：4个三级营养系统中雅脊金小蜂实验种群在4种虫源寄主中均能正常发育,其卵-成虫的发育历期在4种虫源寄主中由短至长依序为：玉米粒-玉米象〈小麦粒-玉米象〈小麦粒-米象〈玉米粒-米象;4种蜂源中雅脊金小蜂对小麦中的米象或玉米象的寄生率、刺死率和总致死率均显著高于对玉米中的米象或玉米象。因此用雅脊金小蜂控制小麦中的米象或玉米象,其效果较之玉米中的米象或玉米象的效果更好。     

八种十字花科寄主植物真叶和子叶的化学成分及其对小菜蛾生长发育及生理代谢的影响

为明确小菜蛾Plutella xylostella对寄主植物真叶和子叶的适合度,于室内测定8种十字花科植物改良青杂3号、改良露头青、陕油0913、甘杂1号、超级火箕青、四月慢、绿球66和中花尖叶芥蓝真叶和子叶的营养物质和次生代谢物质的含量,并测定取食后小菜蛾幼虫的取食选择性、发育历期、蛹重、保护酶和解毒酶活性。结果显示,8种寄主植物真叶的可溶性糖、总氨基酸、单宁、类黄酮和总酚含量之间差异显著,且大部分均显著高于其子叶,8种寄主植物子叶的可溶性糖、总氨基酸、单宁、类黄酮和总酚含量之间也差异显著。小菜蛾3龄幼虫偏好取食真叶;取食8种寄主植物真叶后成虫前期的发育历期为12.3～16.3 d,取食子叶后成虫前期的发育历期为14.3～18.6 d;取食子叶的蛹重明显低于取食其真叶;取食8种寄主植物真叶的小菜蛾幼虫体内超氧化物歧化酶（superoxide dismutase,SOD）、过氧化物酶（peroxidase,POD）、过氧化氢酶（catalase,CAT）、谷胱甘肽S-转移酶（glutathione S-transferase,GST）、羧酸酯酶（carboxylesterase,Car...     

Biology and integrated pest management for the banana weevil Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae)

The banana weevil Cosmopolites sordidus (Germar) is the most important insect pest of bananas and plantains (Musa spp.). The larvae bore in the corm, reducing nutrient uptake and weakening the stability of the plant. Attack in newly planted banana stands can lead to crop failure. In established fields, weevil damage can result in reduced bunch weights, mat die-out and shortened stand life. Damage and yield losses tend to increase with time. This paper reviews the research on the taxonomy, distribution, biology, pest status, sampling methods, and integrated pest management (IPM) of banana weevil. Salient features of the weevil's biology include nocturnal activity, long life span, limited mobility, low fecundity, and slow population growth. The adults are free living and most often associated with banana mats and cut residues. They are attracted to their hosts by volatiles, especially following damage to the plant corm. Males produce an aggregation pheromone that is attractive to both sexes. Eggs are laid in the corm or lower pseudostem. The immature stages are all passed within the host plant, mostly in the corm. The weevil's biology creates sampling problems and makes its control difficult. Most commonly, weevils are monitored by trapping adults, mark and recapture methods and damage assessment to harvested or dead plants. Weevil pest status and control options reflect the type of banana being grown and the production system. Plantains and highland bananas are more susceptible to the weevil than dessert or brewing bananas. Banana production systems range from kitchen gardens and small, low-input stands to large-scale export plantations. IPM options for banana weevils include habitat management (cultural controls), biological control, host plant resistance, botanicals, and (in some cases) chemical control. Cultural controls have been widely recommended but data demonstrating their efficacy are limited. The most important are clean planting material in new stands, crop sanitation (especially destruction of residues), agronomic methods to improve plant vigour and tolerance to weevil attack and, possibly, trapping. Tissue culture plantlets, where available, assure the farmer with weevil-free material. Suckers may be cleaned by paring, hot water treatment and/or the applications of entomopathogens, neem, or pesticides. None of these methods assure elimination of weevils. Adult weevils may also invade from nearby plantations. As a result, the benefits of clean planting material may be limited to a few crop cycles. Field surveys suggest that reduced weevil populations may be associated with high levels of crop sanitation, yet definitive studies on residue management and weevil pest status are wanting. Trapping of adult weevils with pseudostem or corm traps can reduce weevil populations, but material and labour requirements may be beyond the resources of many farmers. The use of enhanced trapping with pheromones and kairomones is currently under study. A combination of clean planting material, sanitation, and trapping is likely to provide at least partial control of banana weevil.Classical biological control of banana weevil, using natural enemies from Asia, has so far been unsuccessful. Most known arthropod natural enemies are opportunistic, generalist predators with limited efficacy. Myrmicine ants have been reported to help control the weevil in Cuba, but their effects elsewhere are unknown. Microbial control, using entomopathogenic fungi and nematodes tend to be more promising. Effective strains of microbial agents are known but economic mass production and delivery systems need further development.     

Inducibility of metabolic insecticide defenses in boll weevils and tobacco budworm caterpillars

Of five cotton allelochemicals, (+)-α-pinene, β-caryophyllene, gossypol, umbelliferone, and scopoletin, all except gossypol induced cytochrome P-450 content, N-demethylation, and epoxidation activities more in tobacco budworm larval midguts than in adult or larval boll weevils. All except gossypol also induced glutathione transferase activity in tobacco budworm larval midguts and adult boll weevils. Microsomal esterase activity was unaffected or suppressed by all five allelochemicals. Soluble esterase activities were unaffected, or induced only in boll weevil larvae. The contrast in insecticide resistance development between the tobacco budworm and the boll weevil may be, in part, related to superior inducibility of cytochrome P-450 and associated activities in the former species in addition to overall higher uninduced activities (26).     

Efficacy of the organic-certified insecticide Diatect II against the boll weevil (Anthonomus grandis) in cotton

The efficacy of the organic insecticide Diatect II against boll weevil (Anthonomus grandis Boheman) in cotton (Gossypium hirsutum L) in the Lower Rio Grande Valley of Texas were assessed in small-plot field trials and greenhouse cage tests using azinphos-methyl treatments as a standard for comparison. Plastic sheets were placed in the furrows of the treated plots to retrieve boll weevils which dropped from the plants after being killed by the insecticides. Samples of live weevils taken by a tractor-mounted vacuum sampler revealed a modest, but significant, reduction in boll weevil populations in Diatect II plots. However, samples of dead weevils indicated that this reduction was due to movement of weevils out of the plots rather than to mortality. This interpretation is supported by greenhouse cage studies, where mortality in Diatect II treated cages was no greater than that in untreated control cages. The effects of insecticide treatments in small plots can be confounded easily and quickly by interplot movement of target insects. Although the relative effects of various compounds can usually be assessed by sampling the populations in plots soon after treatment, the best measure of efficacy is obtained by directly sampling insects that have died in the plot. This parameter is insulated from the effects of interplot movement, unless the toxicant is slow to immobilize the target insect. Taken together, our results indicate little efficacy by Diatect II against boll weevil under our test conditions.     

黄芪根瘤象甲发生规律及生物学特性

为进一步明确黄芪根瘤象甲Sitona simillimus的发生规律和生物学特性,于2016—2019年采用田间系统调查和室内饲养试验对黄芪根瘤象甲的越冬规律、田间数量动态变化、生活习性和各虫态的发育历期进行调查,测定土壤湿度和寄主植物对成虫存活及发育的影响。结果表明,黄芪根瘤象甲以成虫在靠近植物根际处的土层内越冬,越冬适宜的土壤质量含水量为5%~10%。在甘肃省定西市黄芪根瘤象甲1年发生1代,越冬成虫产卵高峰期为每年5月下旬至6月中旬,幼虫发生高峰期为每年6月中旬至8月初,化蛹高峰期为每年7月下旬至8月上旬,成虫羽化盛期为每年8月下旬至9月上旬。黄芪根瘤象甲成虫羽化当年虽可取食,但不产卵,翌年越冬结束后开始取食,取食后即可产卵。在黄芪、红芪、苜蓿和三叶草中,只有取食黄芪叶片的雌成虫才能正常产卵繁殖。黄芪根瘤象甲成虫产卵的昼夜节律明显,产卵主要集中在12：00—22：00,单雌产卵量为2 051.4粒,产卵期为42.6 d。卵、蛹和幼虫的平均发育历期分别为9.8、10.6和36.7 d。     

草地贪夜蛾对金银花的取食适应性

为明确新入侵农业害虫草地贪夜蛾Spodoptera frugiperda对药用植物金银花Lonicera japonica的潜在为害风险,采用室内饲养观察法比较取食玉米Zea mays和金银花叶片后草地贪夜蛾的种群特征,并采用室内生测法测定取食2种植物幼虫体内消化酶和解毒酶的活性。结果显示,草地贪夜蛾在金银花上能完成完整的世代发育。取食金银花叶片的草地贪夜蛾幼虫发育历期为24.08 d,显著长于取食玉米的幼虫发育历期（18.47 d）;取食金银花叶片的幼虫存活率为63.67%,较取食玉米叶片幼虫的存活率78.00%明显降低;取食金银花叶片的草地贪夜蛾雌、雄蛹重分别为197.98 mg和198.78 mg,显著大于取食玉米叶片时;取食金银花和玉米叶片的草地贪夜蛾成虫的繁殖力与寿命均无显著差异。取食金银花叶片的草地贪夜蛾5龄幼虫中肠中的淀粉酶、脂肪酶、胰蛋白酶、谷胱甘肽S-转移酶和细胞色素P450酶的活性均较取食玉米叶片时显著降低,但羧酸酯酶活性较取食玉米叶片时显著升高。表明草地贪夜蛾在金银花上能较好地生长发育和繁殖,这对金银花的安全生产构成潜在威胁。     

Residual activity of spinosad applied as a soil drench to tomato seedlings for control of Tuta absoluta

BACKGROUND

Tuta absoluta (Lepidoptera: Gelechiidae) is difficult to control by means of foliar insecticides, partly because of the endophytic feeding behavior of its larvae. The biopesticide spinosad is applied as a foliar spray for control of T. absoluta and has systemic properties when applied as a soil drench to the growing medium of tomato plants. The aims of this study were to determine the: (i) instar-dependent tolerance of larvae to spinosad; (ii) efficacy of spinosad drench application for the control of larvae; (iii) residual period of systemic activity of spinosad in leaves and fruit after drenching; and (iv) effect of spinosad drenching on tomato plant growth parameters.

RESULTS

The estimated LC₅₀ value (Lethal Concentration at which 50% of the larvae died) differed between instars. The LC₅₀ for second-instar larvae (0.41 ppm) to spinosad was significantly lower than that for third- (0.64 ppm) and fourth-instar (0.63 ppm) larvae. The LC₈₀ value (Concentration at which 80% of the larvae died) for fourth-instar larvae (2.48 ppm) was 2.6- and 1.7-fold higher than that for the second- and third-instar larvae, respectively. The spinosad concentration recorded in leaves at 25 days after treatment (DAT; 0.26 μg g⁻¹) was significantly lower than that in leaves sampled at 3, 10 and 15 DAT. High larval mortalities were, however, recorded for the duration of the experiment, which lasted 25 days (equivalent to one T. absoluta generation).

CONCLUSION

Systemic spinosad effectively controlled T. absoluta larvae over a prolonged period. However, drenching this insecticide violates the recommendation of the Insecticide Resistance Action Committee to avoid treating consecutive insect generations with the same mode of action and can therefore result in the evolution of insecticide resistance. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Het parasitaire karakter van Septotinia populiperda Waterman & Cash

Summary Mature apothecia ofSeptotinia populiperda Waterman andCash are formed in spring and early summer on leaves shed the previous autumn. The ascospores ofS. populiperda produce an infection in the form of leafblotches only when an injury of the leaf is present.P. candicans Ait. is more susceptible to the parasite thanP. marilandica Bosc. andP. brabantica Houtz. Leafblotches are produced in equal numbers when the ascospores are sprayed with an atomizer upon the upper or the lower leafsurface. The germination of the ascospores is inhibited in vitro at a concentration of 7 to 8 mg copper per liter, when copper is used as Bordeaux mixture, or as coppersulfate (CuSO₄5H₂O).     

缩节胺处理棉株对棉铃虫的影响初报

棉株施用缩节胺后能减少棉铃虫(Heliothis armigera Habner)在棉株上的落卵量48.8%—88%,田间虫量减少39.5%—77.3%,取食嫩叶、花蕾后的2龄幼虫体重下降、发育历期延长,死亡率增加,化蛹率和羽化率都有下降,总的生存率降低了57.62%。测定表明施用缩节胺后,棉株各部组织内棉酚有增加趋势,以蕾内增加较多,为49%—92.1%,铃壳次之,为13.8%—65.5%,叶内较少,为3.6%—39.7%。而单宁量除大铃壳内有增外,大多下降。施用次数与剂量的增加,与棉酚量的提高有共同趋势。花蕾期施用,棉酚量的增加高于花铃期。     

High‐level of resistance to spinosad,emamectin benzoate and carbosulfan in populations of Thrips tabaci collected in Israel

BACKGROUND: The onion thrips, Thrips tabaci Lindeman, is a major pest of several crop plants in the genus Allium, such as onions, garlic and chives. In Israel, these crops are grown in open fields and in protected housing. This thrips is usually controlled by the application of chemical insecticides. In recent years, spinosad, emamectin benzoate and carbosulfan have been the major insecticides used for the control of the onion thrips. In the last 4 years, growers of chives and green onion from several regions of Israel have reported a significant decrease in the efficacy of insecticides used to control the onion thrips. RESULTS: The susceptibility of 14 populations of the onion thrips, collected mainly from chives between the years 2007 and 2011, to spinosad, emamectin benzoate and carbosulfan was tested using a laboratory bioassay. The majority of the populations showed significant levels of resistance to at least one of the insecticides. LC₅₀ values calculated for two of the studied populations showed that the resistance factor for spinosad compared with the susceptible population is 21 393, for carbosulfan 54 and for emamectin benzoate 36. Only two populations, collected from organic farms, were susceptible to the insecticides tested. CONCLUSION: This is the first report of a high resistance level to spinosad, the major insecticide used to control the onion thrips. Resistance cases to spinosad were associated with failures to control the pest. Populations resistant to spinosad also had partial or complete resistance to other insecticides used for controlling the onion thrips. Copyright © 2012 Society of Chemical Industry     

Reduction of banana weevil populations with pseudostem traps

Abstract

One‐week‐old traps made from split banana pseudostems were 1.5–1.7‐fold more attractive to adult banana weevils than 2–3‐week‐old traps. In one experiment, all available pseudostem material was used for trapping, and weekly collecting of weevils over an 11‐month trapping period led to a 50% reduction in weevil catches in one field. In another field with a lower initial weevil density the trapping did not reduce weevil populations. In another experiment, the effect of intensive use of pseudostem traps and daily collecting of trapped weevils was estimated by a mark and recapture method over a period of 6 weeks. Reductions in weevil densities were calculated using a modified version of the Lincoln‐Index. Weevil populations were reduced by 48.5% after 3 weeks and by 62.5% after 6 weeks. Trapping efficiency declined during the experiment and appeared to be related to weevil population densities. This cultural control system may be effective in weevil control in small‐farm situations where labour availability is not a limiting factor.     

Field trial on the effects of the herbicide MCPA on ixodid ticks

Abstract

Studies were conducted to develop a pheromone‐trap monitoring system for the sweet potato weevil, Cylas formicarius (Fabricius), in sweet potato, Ipomoea batatas (L.) Lam., fields in four states: Florida, Louisiana, North Carolina, and Texas. The present studies examined the attractiveness of sex pheromone synthesized by two sources (USDA and AgriSense) and pheromone of different purities (75–99%) to weevils in the field. In all but one trial, weevil counts did not differ between traps baited with pheromone from the two sources for each of two doses (10 and 100 μg). Percentages of weevils caught per replicate per sample date were not consistently positively correlated with purity (significant in four of 10 trials); however, slope estimates were steeper in regions with lower trap counts (North Carolina and Louisiana) than in those with higher trap counts (Florida). Because the pheromone will be used to monitor weevils In both weevil‐free and weevil‐infested regions, the use of pheromone with a purity level >99% is most appropriate. The importance of these data in pheromone‐trap monitoring programmes for this weevil worldwide is discussed.     

Over het verband tussen de aantasting door de koolzaadgalmug,Dasyneura brassicae Winn. (Diptera,Itonididae) en de Koolzaadsnuitkever,Ceuthorrhynchus assimilis Payk. (Coleoptera,Curculionidae)

Samenvatting De tegenstrijdige meningen, die bestaan over de vraag of de koolzaadga Imug (Dasyneura brassicae Winn.) voor zijn ei-afzetting is aangewezen op beschadigde hauwen, gaven aanleiding dit punt nader te onderzoeken. Uit infectieproeven, waarbij de galmug òf planten met uitsluitend gave òf planten met beschadigde hauwen kreeg aangeboden om zijn eieren te leggen, bleek, dat deze eieren uitsluitend in de van te voren beschadigde hauwen werden gevonden. Ook waarnemingen over het gedrag van de mug in het veld ondersteunden de opvatting, dat de eieren uitsluitend door reeds bestaande boorgaten in de hauw worden afgezet. De koolzaadsnuitkever (Ceuthorrhynchus assimilis Payk.) zal ongetwijfeld de belangrijkste veroorzaker van deze beschadigingen zijn. De bestrijding van de kever zal in de regel niet in staat zijn het aantal beschadigde hauwen zo sterk te verminderen, dat de eerste galmugvlucht geen gelegenheid tot ei-afzetting meer heeft. Door de vermindering van het aantal keverlarven als gevolg van de effectieve keverbestrijding, kan een vermindering van het a antal uitkruipgaten der larven bereikt worden, die wèl belangrijk is, daar de tweede galmugvlucht voor ei-afzetting vooral op deze gaten is aangewezen.

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On the relation between the infestation by the cabbage seed pod midge, Dasyneura brassicaeWinn. and the seed pod weevil, Ceuthorrhynchus assimilisPayk

Summary The controversy of whether or not the cabbage seed pod midge (Dasyneura brassicae Winn.) uses only damaged pods for depositing its eggs was reason for further investigation. Experiments with potplants were started. Midges were caged on colza-plants which had only undamaged pods as well as on plants which had pods artificially damaged by prickling with a needle. Eggs were only found in the damaged pods. The behaviour of the midge in the field, when it is intending to oviposite, also shows its need for damaged places as the midges were observed continuously walking on the pods, trying with their ovitubus to find a hole in the wall of the pod. The cabbage seed pod weevil (Ceuthorrhynchus assimilis Payk.) is undoubtedly the chief contributor to the number of damaged pods. Economic control of this weevil will only have a limited indirect effect on infestation by the first midge flight. However as it reduces the number of pods with weevil larvae, it reduces the number of exit holes in the pods. These exit holes are especially used by the second midge flight which therefore is controlled indirectly to some extent.

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Destijds werkzaam bij het Instituut voor Plantenziektenkundig Onderzoek (I.P.O.) te Wageningen; thans werkzaam bij het Laboratorium voor Entomologie van de Landbouwhogeschool te Wageningen.     

10th British Weed Control Conference

The performance of different spray droplet spectra of cypermethrin from cone nozzles applied to brassica leaves was evaluated by bioassay using Plutella xylostella larvae. A spray droplet spectrum containing small droplets (VMD = 119 μm) caused a significantly higher knockdown and mortality compared to a coarser spray (VMD = 210 μm). No significant difference in the responses was observed when cypermethrin was sprayed over the top of the plants compared to plants sprayed from both sides using either nozzle; but the fine spray consistently gave better knockdown and mortality regardless of spray direction. The results indicated that spray effectiveness of cypermethrin could be improved by using a fine spray nozzle.     

Impact of spray application methodology on the development of resistance to cypermethrin and spinosad by fall armyworm Spodoptera frugiperda (JE Smith)

The development of resistance to an insecticide under various types of application method has yet to be reported in the literature. Five fall armyworm Spodoptera armigera (JE Smith) colonies were reared in a chamber for ten generations before starting topical application bioassays. From each colony, 200-500 third-fourth-instar larvae were fed for 72 h on corn plants sprayed with cypermethrin or spinosad at minimum application rate (20 g ha(-1)) using a small droplet size nozzle XR8001VS (volume median diameter D(v0.5) = 163 microm) or a large droplet size nozzle XR8008VS (D(v0.5) = 519 microm). Surviving larvae were transferred to untreated corn leaves to complete their life cycle. Next-generation third-instar larvae of each colony were topically dosed with technical cypermethrin or spinosad at 1 microL per larva, and mortality was recorded 24 h post-treatment. The results indicated that cypermethrin demonstrated an insecticidal activity greater than that of spinosad, and the cypermethrin regression lines moved to the right faster than those for spinosad, indicating an increased tolerance of cypermethrin. Generally, larvae from all generations (F1-F7) under the XR8008VS treatments were less susceptible to cypermethrin and developed resistance faster and to higher levels than larvae from the XR8001VS treatments. The confidence limits (95%) of LD(50) for all spinosad treatments indicated that there was no significant difference from the LD(50) value of the susceptible reference strain. The results are a first indication that application technology/insecticide reaction may affect the rapidity of resistance development in certain pest/plant scenarios, but field studies are needed to confirm this conclusion.