Toxicity of insecticides to the sweetpotato whitefly (Hemiptera: Aleyrodidae) and its natural enemies

Efficient chemical control is achieved when insecticides are active against insect pests and safe to natural enemies. In this study, the toxicity of 17 insecticides to the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the selectivity of seven insecticides to natural enemies of this insect pest were evaluated. To determine the insecticide toxicity, B. tabaci adults were exposed to abamectin, acephate, acetamiprid, cartap, imidacloprid, malathion, methamidophos, bifenthrin, cypermethrin, deltamethrin, esfenvalerate, fenitrothion, fenpropathrin, fenthion, phenthoate, permethrin and trichlorphon at 50 and 100% of the field rate (FR), and to water (untreated control). To determine the insecticide selectivity, adults of Encarsia sp., Acanthinus sp., Discodon sp. and Lasiochilus sp. were exposed to abamectin, acephate, acetamiprid, cartap, imidacloprid, malathion and methamidophos at 50 and 100% FR, and to water. Groups of each insect species were exposed to kale leaves preimmersed in each treatment under laboratory conditions. Mortality of exposed individuals was recorded 24 h after treatment. Cartap and imidacloprid at 50 and 100% FR and abamectin and acetamiprid at 100% FR showed insecticidal activity to B. tabaci adults. Abamectin at 50 and 100% FR was the least insecticidal compound to the natural enemies Acanthinus sp., Discodon sp. and Lasiochilus sp. The present results suggest that abamectin at 100% FR may decrease B. tabaci field populations but can still be harmless to predators. Implications of these results within an integrated pest management context are discussed.     

Effectiveness of two insect growth regulators against Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) and Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) and their impact on population densities of arthropod predators in cotton in Pakistan

Field efficacies of two insect growth regulators (IGRs) at two recommended application rates, buprofezin at 370 and 555 g AI ha(-1) and lufenuron at 37 and 49 g AI ha(-1), were determined against the sweet potato whitefly, Bemisia tabaci (Gennadius), and the cotton bollworm, Helicoverpa armigera (Hübner), in experimental plots of cotton at the Directorate of Cotton Research, Faisalabad, Pakistan. Adverse effects of the IGRs on populations of associated arthropod predators, namely geocorids, chrysopids, coccinellids, formicids and arachnids, were also assessed. Both IGRs significantly reduced populations of B. tabaci at each application rate 24, 48 and 72 h after treatment, and higher doses were more effective than lower doses. Buprofezin was not effective against H. armigera at any tested dose for any time of treatment in any spray. Lufenuron applied at 37 and 49 g AI ha(-1) effectively suppressed H. armigera populations, resulting in significant reductions in crop damage. At lower doses, both IGRs appeared safe to predator populations, which did not differ significantly in IGR-treated versus untreated control plots. Population densities of formicids and coccinellids were significantly lower at high concentrations of both IGRs in treatment plots, possibly as a result of reduced prey availability. The potential role of buprofezin and lufenuron for control of B. tabaci and H. armigera in a spray programme and the likelihood of direct toxic effects of IGRs on predatory fauna of cotton are discussed.     

Targeting Cydia pomonella (L.) (Lepidoptera: Tortricidae) adults with low‐volume applications of insecticides alone and in combination with sex pheromone

BACKGROUND: Studies surveyed the toxicity of several insecticides against adult codling moth, Cydia pomonella (L.), and examined the field effectiveness of applying low‐volume (12 L ha^?1) sprays alone or in combination with a microencapsulated (MEC) sex pheromone formulation. RESULTS: Neonicotinyls, organophosphates and synthetic pyrethroids significantly reduced fecundity at concentrations nearly 100‐fold lower than their maximum labeled field rate. Field studies in 2005 demonstrated that six applications of esfenvalerate resulted in > 90% reduction in fruit injury versus the untreated check. The addition of the MEC pheromone formulation did not further improve control. Five sprays of esfenvalerate, phosmet and acetamiprid all significantly reduced levels of fruit injury compared with the untreated control in 2006. Esfenvalerate and acetamiprid mixed with the MEC pheromone significantly reduced fruit injury compared with the MEC‐only treatment. Significant increases in pest and decreases in predator mite densities occurred in plots treated with esfenvalerate in both years. Low‐volume sprays of phosmet and acetamiprid did not disrupt mites. CONCLUSION: Low‐volume insecticide sprays can effectively manage codling moth and are less disruptive of integrated mite management. Developing an effective ‘attract and kill’ technology with this approach will require optimization of the attractant(s) to maximize moth exposure to insecticide residues. Published 2010 by John Wiley & Sons, Ltd.     

释放巴氏新小绥螨防治温室大棚番茄上的烟粉虱

烟粉虱是一种世界性重大害虫,随着杀虫剂的抗药性问题以及在蔬菜上的残留问题日益严重,生物防治成为解决这一问题的重要措施。本文研究了释放巴氏新小绥螨对温室大棚番茄上自然发生的烟粉虱种群的控制作用。结果表明:释放巴氏新小绥螨,对温室大棚番茄上的烟粉虱的种群具有明显的压制作用;温室大棚番茄上烟粉虱种群,在释放捕食螨和常规对照处理间的总体动态趋势相同,烟粉虱的数量在番茄植株上的分布均为上部中部下部叶片,但常规对照处理的烟粉虱数量是释放捕食螨处理的2～3倍;在烟粉虱种群密度低时,释放巴氏新小绥螨的防治效果较好,达到90%以上,随着烟粉虱密度的增大,巴氏新小绥螨对烟粉虱的防治效果下降,但番茄拉秧时防效仍可达到55.70%。相比化学农药,释放巴氏新小绥螨的生物防治措施对治理烟粉虱更具有稳定性和长效性的优势。     

棉田间作蔬菜防治B型烟粉虱

在室内用"Y"形嗅觉仪以棉花为对照测定了B型烟粉虱对6种蔬菜的选择性,不同蔬菜对B型烟粉虱诱集率的大小为:菜豆花生茴香芫荽芹菜韭菜。除了烟粉虱对菜豆的选择系数为正值外,烟粉虱对其他几种蔬菜的选择系数均为负值。6种蔬菜与棉花间作,结果表明:间作棉花上的烟粉虱成虫数量与对照存在显著差异。除了间作菜豆棉花上的烟粉虱成虫数量比对照增加外,间作花生、茴香、芫荽、芹菜、韭菜的棉花上烟粉虱成虫数量比对照均减少。     

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.     

Evaluation of food sprays and relay strip crops for enhancing biological control of bollworms and cotton aphids in cotton

Studies were conducted at the Texas Agricultural Experiment Station research farms located at Munday (1996 test) and Chillicothe (1997 test) to evaluate relay strip crops in combination with a food spray to enhance biological control of bollworms, Helicoverpa zea (Boddie), and cotton aphids, Aphis gossypii Glover, in cotton. The relay crops included fall plantings of hairy vetch, Vicia villosa Roth, and canola, Brassica napus L., and a spring planting of grain sorghum, Sorghum bicolor L. Cotton, Gossypium hirsutum L., was planted between the relay crops or was isolated from the relay crops. Treatments within the two cotton systems included an untreated check plot, a plot sprayed with sugar+yeast (food spray) during summer to attract and hold predator insects, a plot sprayed with biological ('soft') insecticides for bollworm and cotton aphid control (Bacillus thuringiensis and pymetrozine, respectively), and a plot sprayed with harsh insecticides for bollworm and cotton aphid control (zeta cypermethrin and dicrotophos or profonofos, respectively). A split-plot experimental design, with three replications, was used where whole plots included relay and isolated cotton systems and subplots were the four food/chemical treatments. Predator numbers were monitored with a vacuum sampler once a week in relay crops and cotton. Bollworms and cotton aphids were monitored visually once a week in cotton during July and August. Total predator numbers were higher in cotton adjacent to relay crops in 1996, but not in 1997. The food spray did not enhance attraction and retention of predators either year. Bollworm larval numbers were significantly higher in relay cotton, food spray plots in 1996. Bollworm larval numbers were similar in relay and isolated cotton, and larval numbers were significantly reduced only in the plot where zeta cypermethrin (harsh insecticide plot) was used. In 1996, cotton aphid numbers in the relay cotton system were significantly higher in the untreated check plots in relation to numbers in the food spray, soft insecticide, and harsh insecticide plots, which were statistically similar. In the isolated cotton system, aphid numbers were highest in untreated plots, intermediate in food spray and soft insecticide plots, and lowest in the harsh insecticide plots. Aphid numbers increased more rapidly in the harsh insecticide plots that had been treated previously for bollworm control. The food spray and pymetrozine treatments reduced cotton aphids more effectively in the relay cropping system than in the isolated cotton system. Bollworms and cotton aphids did not reach pest status in 1997. The combination of a relay cropping system with a food spray did not enhance predator numbers and did not aid in retention of predators in cotton during August. Sucrose in the food spray attracted high numbers of bollworms in 1996.     

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。     

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.     

Susceptibility of field populations of adult Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) and Eretmocerus sp (Hymenoptera: Aphelinidae) to cotton insecticides in Burkina Faso (West Africa)

Research was conducted in 14 cotton fields (3-10 ha) selected in seven localities (two fields per locality) in Burkina Faso, with the objectives of: (1) estimating Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) population abundance, (2) assessing the levels of parasitism by Encarsia spp and Eretmocerus spp (Hymenoptera: Aphelinidae) and (3) estimating the susceptibilities of the pest and of an Eretmocerus sp to the insecticides currently sprayed on cotton. Yellow sticky cards and a leaf-turning technique were used to estimate adult B. tabaci population densities. Yellow sticky cards were also used to estimate the densities of adult Eretmocerus sp and the susceptibilities of B. tabaci to insecticides. Leaf disk techniques were used to estimate B. tabaci red eye nymph populations and parasitism by Encarsia spp and Eretmoceus spp was evaluated using stereo-microscopy. A leaf cage technique was used to estimate the susceptibilities of Eretmocerus sp to insecticides. A mean of 6.5-27.4 adult B. tabaci were trapped per yellow sticky card and 5.5 to > 34.9 were counted per leaf using the leaf turning technique. There were 0.14-13 Eretmocerus sp trapped per yellow sticky card. The levels of parasitism varied between 36 and 87% by the end of the season and parasitism by Eretmocerus sp predominated in most of the fields. The susceptibilities of B. tabaci and Eretmocerus sp varied from field to field and with the insecticide tested.     

Effects of host plants on insecticide susceptibility and carboxylesterase activity in Bemisia tabaci biotype B and greenhouse whitefly, Trialeurodes vaporariorum

Bemisia tabaci (Gennadius) biotype B and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), have become serious pests of cotton and vegetable crops in China since the early 1990s. In recent years, however, B. tabaci have broken out more frequently and widely than have T. vaporariorum. The B. tabaci biotype B has also developed higher resistance to several insecticides. Here, the effects of four different host plants on the insecticide susceptibility of B. tabaci biotype B and T. vaporariorum have been compared. The LC(50) values of imidacloprid, abamectin, deltamethrin and omethoate in T. vaporariorum reared on cucumber were significantly higher than those in B. tabaci (the LC(50) values in T. vaporariorum were respectively 3.13, 2.63, 2.78 and 6.67 times higher than those in B. tabaci). On the other hand, the B. tabaci population reared on cotton was more tolerant to all four insecticides tested than the T. vaporariorum population from the same host, especially to abamectin (up to 8.4-fold). The effects of the four host plants on the activity of carboxylesterase (CarE) in B. tabaci biotype B and T. vaporariorum were also compared. The results showed that, although the CarE activity of B. tabaci and T. vaporariorum varied depending on the host plants, the B. tabaci population possessed significantly higher CarE activity than the T. vaporariorum population reared on the same host plant. This was especially so on cucumber and cotton, where the CarE activities of the B. tabaci population were over 1.6 times higher than those of T. varporariorum. The frequency profiles for this activity in B. tabaci and T. vaporariorum populations reared on same host plant were apparently different.     

Insect Growth Regulators and their Potential in the Management of Stored-product Insect Pests

Concern about the impact of pesticides on both health and environment has resulted in the search for alternative control measures for stored-product insect pest. Amongst such alternatives are insect growth regulators (IGRs), a class of biorational compounds that disrupt the normal development of insects. Because of their selectivity of action, these compounds appear to fit the requirements for Third Generation Pesticides, environmentally benign and safer grain protectants. IGRs have been developed commercially and are being used to control insect pests in agriculture, forestry, public health and stored products. IGRs affect the biology of treated insects, for example, both embryonic and post-embryonic development, reproduction, behaviour and mortality. Abnormal morphogenesis is the observed effect of IGR action on the insects. Many of them are more potent than current insecticides, even against the eggs.Compared with the conventional insecticides, IGRs do not exhibit quick knock-down in insects or cause mortality, but the long-term exposure to these compounds largely stops the population growth, as a result of the effects mentioned in both the parents and progeny.The present paper focuses on the previous works on different IGRs available commercially. Also, their possible role in the management of stored-product insect pests has been discussed.     

New ways and new hopes for IGR development

Insect Growth Regulators (IGRs) represent advanced, bio-rational insecticides. This Special Issue reflects progress in IGR development that has been enabled by insight into the molecular principles of biosynthetic or hormone signaling pathways. The unifying principle is aiming at processes and molecular targets that are unique to arthropods and ideally to narrower insect taxa representing pests or disease vectors. While some strategies of obtaining the desired compounds for chemical intervention rely on rational, structure-based design or computational power, others exploit technologies allowing automated, high-throughput screening of large chemical libraries. All avenues leading to selective and environmentally safe pest control are valid as we face the imminent threat of the declining world insect population.     

Relative effects of the insecticide thiamethoxam on the predator Podisus nigrispinus and the tobacco whitefly Bemisia tabaci in nectaried and nectariless cotton

The predaceous stinkbug Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) feeds on plants as well as on arthropod prey. The question arises whether feeding on plants might expose the predator to systemic insecticide via ingestion of the active ingredient or its metabolites through plant sap of treated plants. This interaction was investigated with nectaried and nectariless cotton plants cropped in pots and treated with the systemic insecticide thiamethoxam at 0.5, 1.0 and 2.0 mg per plant as a root drench. Development of P. nigrispinus fed on prey and on treated nectaried and nectariless cotton plants and confined at 15, 30 and 45 days after insecticide application, and adult reproduction from nymphs caged 30 days after treatment were determined. Podisus nigrispinus life history traits were unaffected by the type of cotton plant, nectaried or nectariless, but were significantly affected by insecticide dose and time after application. Developmental time was extended and fresh adult body weight was reduced by feeding on prey and treated plants. Nymphs caged on treated plants with the highest thiamethoxam concentration at 15 days after application produced only 13.2% of adults. Females emerged from nymphs caged on both plants and at all thiamethoxam concentrations at day 30 after application presented similar reproductive characteristics, except for age of first oviposition, which was delayed on plants treated with the highest thiamethoxam concentration. Thiamethoxam at 0.5 mg per plant restrained tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) colonization only during the first 15 days after application to either cotton plant, and similar immature densities were sampled at day 35 after application on treated and untreated plants. However, plants treated with 1.0 and 2.0 mg per plant as a drench and cropped in pots were protected from tobacco whitefly for up to 45 days after exposure to a whitefly colony.     

Accumulation pattern and insecticidal effect of aldicarb in cotton following soil treatment for the control of the tobacco whitefly (Bemisia tabaci)

The accumulation pattern of the pesticide aldicarb [2-methyl-2-(methylthio) propionaldehyde O-(methylcarbamoyl)-oxime] and of its sulfoxide and sulfone metabolites was studied in field-grown cotton, following soil treatments at various intervals from planting. Control of the tobacco whitefly(Bemisia tabaci) was determined and correlated with the concentration of aldicarb and of its metabolites in cotton leaves. The main constituent found in the leaves was aldicarb sulfoxide, which reached its maximum concentration there at about 22 days post-treatment. Late application of the insecticide (mid-July) resulted in higher concentrations toward the end of the growing season and so gave improved control of the pest. Results are presented for residues in young and mature leaves and in the seeds.     

敦煌市棉田烟粉虱的种群数量动态及防治

2006年4～9月系统调查敦煌市杨家桥乡棉田烟粉虱的种群动态及5种药剂防治效果.结果表明:敦煌市棉田5月下旬始见烟粉虱成虫,6月下旬开始普遍发生,8月上旬形成第一个成虫高峰,至9月中下旬随棉花采摘和气温的下降田间成虫数量逐渐减少.烟粉虱在不同的棉花品种上发生数量不同,敦棉V3上虫量显著低于另外4个品种.5种农药对烟粉虱的防治效果存在显著差异,其中阿克泰、蚧虱傲克药效最好,其3 d后的校正防效分别为88.86%、82.66%.     

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.     

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.     

棉花害虫综合防治中高效低毒农药的选用技术

经过调查研究,明确了换种转B.t基因抗虫棉后棉田虫害的新变化,制订了以防治棉蚜和棉叶螨为重点的兼治棉铃虫及其他害虫的新策略,并通过近几年的农药田间药效试验,鉴定出用48%多杀霉素悬浮剂、2.5%高效氯氟氰菊酯微乳剂、4.5%高效氯氰菊酯乳油、18%高氯·辛乳油、0.5%甲氨基阿维菌素苯甲酸盐乳油防治棉铃虫;用10%吡虫啉可湿性粉剂、10%烟碱水剂、20%啶虫脒可湿性粉剂防治棉蚜;用20%哒螨灵可湿性粉剂、1%阿维菌素乳油防治棉叶螨等高效低毒农药及其配套使用技术。