Effect of milbemectin on the sweetpotato whitefly,Bemisia tabad

Milbemectin has a chemical structure close to the group of avermectins, which are derived fromStreptomyces avermitilis, and is considered primarily an efficient miticide. Effects of milbemectin on the sweetpotato whitefly,Bemisia tabaci Gennadius, were investigated under laboratory and field conditions. In bioassays conducted under controlled chamber conditions, the compound affected 1st instars ofB. tabaci, resulting in a LC₉₀ of 0.06 mg a.i. I-1. Later stage larvae were much less affected. Milbemectin is highly photodegradable in sunlight. In laboratory assays, when treated cotton seedlings were subjected to 3 h of sunlight before being exposed toB. tabaci adults, no mortality of the whiteflies was observed. Milbemectin at a concentration of 2 mg a.i. I-1 applied in combination with 0.2% ‘Ultra Fine’ mineral oil showed a residual activity of 67% adult mortality 10 days after application, whereas milbemectin alone had no appreciable activity. The effect of milbemectin on whitefly populations in a cotton field was compared with that of cypermethrin and of untreated control. Although milbemectin was not applied with mineral oil, it was more effective than cypermethrin in controlling the whitefly populations. This insecticide/miticide seems not to affect appreciably natural enemies ofB. tabaci. Milbemectin may be considered a compound with the potential for controllingB. tabaci populations. Mineral oils enhanced the potency of milbemectin on both whitefly larvae and adults. http://www.phytoparasitica.org posting July 27, 1999. Contribution No. 501/99 from the Inst. of Plant Protection, Agricultural Research Organization.     

Toxicity and growth-suppression exerted by diafenthiuron in the sweetpotato whitefly,Bemisia tabaci

Diafenthiuron (CGA 106 ’630), a thiourea, was sprayed prior to a 48-h infestation by adult females of the sweetpotato whiteflyBemisia tabaci Gennadius, on cotton seedlings under greenhouse conditions; it subsequently suppressed strongly progeny formation of the whitefly, resulting in approximately 50% progeny formation relative to control at 5 mg a.i./l. When the different development stages were separately sprayed directly, the larval stage was the most susceptible, resulting in 50% and 90% mortality of 2nd instars at concentrations of 6.5 and 49.2 mg a.i./l, whereas the LC50 values of adults and pupae were 23 and 45 mg a.i./l, respectively. A mild (30–35%) reduction of egg hatch was obtained at a range of 5–125 mg a.i./l. Thus the potency of diafenthiuron against various stages was in the order larvae > adults > pupae > eggs. Diafenthiuron exhibited a low vapor phase toxicity and had no translaminar effect when tested on first instars ofB. tabaci. The high potency of diafenthiuron against whiteflies described herein, against aphids and mites, as stated in the literature, and against some lepidopterous pests, render this compound an important insect control agent for pests of cotton and other crops.     

First record of the Q Biotype of the sweetpotato whitefly, Bemisia tabaci, intercepted in the UK

For the UK, Bemisia tabaci poses a threat primarily to protected vegetable crops due to the transmission of several plant-pathogenic viruses. There are at least 24 different biotypes of B. tabaci that cannot be differentiated through morphological traits. The B (Middle East-Asia Minor 1 species) and Q (Mediterranean species) biotypes are widely considered to be the most important and, as such, the ability to rapidly and precisely biotype B. tabaci interceptions is vital when developing effective control strategies. Intercepted adult/pupal B. tabaci received from the UK Plant Health and Seeds Inspectorate (PHSI) during 2002–2003 (n?=?60) and 2010–2011 (n?=?42) were both biotyped and tested for the presence of Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) using a real-time PCR assay based on TaqMan? chemistry. The positive results indicated that during 2002–2003 the Q biotype comprised 68.3?% of the interceptions whilst in 2010–2011 it comprised 66.7?% of the B. tabaci samples intercepted. Only three of the B biotypes collected during 2002–2003 were positive for TYLCSV, two originating from Israel and the other of unknown origin. The implications in regards to pest management of the insect are discussed.     

The use of isozyme patterns to distinguish sweetpotato whitefly (Bemisia tabaci) biotypes

Recent collections ofBemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) from California desert regions represent a mixture of biotypes. One biotype was identical to a culture originally obtained in 1981 and since maintained in the laboratory. The other and most prevalent biotype could not be distinguished morphologically but could be distinguished by esterase isozyme banding patterns. The banding patterns of the biotypes were not affected by culturing the whiteflies on different plant species. Different developmental stages, and adults of both sexes, had the same isozyme patterns.     

Diagnosis and characterization of insecticide-insensitive acetylcholinesterase in three populations of the sweetpotato whitefly Bemisia tabaci

A biochemical approach was used to characterize acetylcholinesterase (AChE) insecticide insensitivity in several sweetpotato whitefly (Bemisia tabaci; SPW) populations. Discriminating doses of insecticide were established to differentiate between sensitive and insensitive SPW strains and to genotype individual whitefly. This technique was then used to examine the frequency of insensitive AChE alleles in several SPW populations and to isolate a line homozygous for insensitive AChE from a heterogenous B-type population. Inheritance of putative altered AChE genotypes was consistent with the proposed haplo-diploid status of B. tabaci. This biochemical diagnostic was also employed to determine the role of insensitive AChE in the observed resistance profiles of several laboratory populations subjected to different selection regimes. In keeping with previous studies on insecticide resistance in SPW, resistance does not appear to be uniquely associated with the B-type but rather with SPW populations found in crop systems. © 1998 SCI.     

Biological activity of natural phytoecdysteroids from Ajuga iva against the sweetpotato whitefly Bemisia tabaci and the persea mite Oligonychus perseae

BACKGROUND: Ecdysteroids are steroid hormones that control moulting and govern several changes during metamorphoses in arthropods. The discovery of the same molecules (phytoecdysteroids) in several plant species displayed a wide array of rather beneficial agricultural impact. Many representatives of the genus Ajuga plants contain phytoecdysteroids with a 5β‐7‐ene‐6‐one system exhibiting physiological activities in insects. RESULTS: By means of chromatographic (silica gel column, TLC) and LC‐MS, two major ecdysteroids (20‐hydroxyecdysone and cyasterone) have been isolated and identified from Israeli carpet bugle Ajuga iva (L.) Schreber (Lamiales: Lamiaceae) plants. Ajuga iva extract fractionated on the silica gel column yielded two fractions that showed high activity against the sweetpotato whitefly Bemisis tabaci and the persea mite Oligonychus perseae. A dose of 5 mg AI L^?1 of the purely identified A. iva ecdysterone significantly reduced fecundity, fertility and survival of these pests, while commercial 20‐hydroxyecdysone at the same dose had lesser effects. CONCLUSION: The results demonstrate considerable efficacy of natural phytoecdysteroids against major agricultural pests, and suggests that these materials should be considered for potential development of friendly control agents. Copyright © 2011 Society of Chemical Industry     

Pathogenicity ofVerticillium lecanii to different developmental stages of the silverleaf whitefly,Bemisia argentifolii

Thirty-five strains ofVerticillium lecanii which originated from different hosts and geographical locations were tested as potential biocontrol agents against silverleaf whitefly,Bemisia argentifolii Bellows & Perring. All strains were tested for their pathogenicity to third-instar nymphs. Several isolates which exhibited high pathogenicity to nymphs were also tested against eggs, pupae and adults ofB. argentifolii. Eggs were found to be immune to infection, but mortality of hatching nymphs reached 95–98%. The rate of hatching nymphs’ infection depended on the age at which the eggs were inoculated and the strain’s virulence. Mortality of nymphs recorded on day 4 after inoculation varied from 0.5±0.3% to 83±2.4%; that of the control ranged from 2.5% to 10.2%. The most virulent strains, with LT₅₀ ranging between 3.2 and 3.8 days, were isolated from aphids in Israel and probably have a similar origin. The pathogenicity ofV. lecanii strains to pupae 6 days after inoculation varied between 59± 12.1 % and 72.5± 13.1 %, as compared with natural mortality of 13.5±4%. The maximum adult mortality caused byV. lecanii strains was between 34.1±5.1% and 52.6±3.8%.     

Biochemical and molecular mechanisms of diafenthiuron resistance in the whitefly,Bemisia tabaci

B-biotype Bemisia tabaci has developed high levels of resistance to many insecticides. To investigate the risks and explore possible mechanisms of resistance to diafenthiuron in B. tabaci, a 32.8-fold diafenthiuron-resistant strain (R-DfWf) was established after selection for 36 generations compared with the susceptible strain (S-Lab). Biochemical assays showed that the activity of cytochrome P450 towards p-NA was significantly higher (4.37-fold higher) in the R-DfWf strain than in the S-Lab strain. Similarly, the carboxylesterase (COE) activity and glutathione S-transferase (GST) activity were also significantly higher (3.12- and 1.83-fold higher, respectively) in the R-DfWf strain than in the S-Lab strain. The expression of five of seven P450 genes was significantly higher (>3-fold) in the R-DfWf strain than in the S-Lab strain. The expression of COE2 was significantly higher (>2.5-fold) in the R-DfWf than in the S-Lab strain. The expression of GST and GST2 was significantly higher (>2.3-fold) in the R-DfWf than in the S-Lab. Thus, cytochrome P450, COE and GST may appear to be responsible for the resistance to diafenthiuron in B. tabaci. It is also valuable for usage of insecticides for resistance management and control of this species.     

The importance of pH in food selection by the tobacco whitefly,Bemisia tabaci

The tobacco whitefly,Bemisia tabaci Gennadius, was found to differentiate between pH values at the leyel of 0.25. It had a clear preference for media with pH values of 6.0 to 7.25 offeredin vitro, in both choice and no-choice situations, when “resting whiteflies” or survival was measured. The whiteflies showed a clear preference for a sucrose concentration of 15%. The addition of 10% sucrose to buffers at various pH values did not change the pattern of their pH preference. Inin vivo experiments whiteflies preferred old cotton leaves (120 days) to younger leaves (60 days). The pH of old leaves was 6.8 while that of young leaves was 5.9. These results may explain the fact that whiteflies attacked cotton plants in commercial fields only late in the season, when the pH values of the cotton leaves exceeded pH 6.     

海氏桨角蚜小蜂对两种生物型烟粉虱的功能反应研究

本文报道海氏桨角蚜小蜂Eretmocerus hayati在室内对不同寄主密度下的B型和Q型烟粉虱Bemisia tabaci寄生和取食情况,并比较了该蜂对两种生物型烟粉虱功能反应的差异。结果表明,海氏桨角蚜小蜂对两种生物型烟粉虱的寄生率和致死率可分别达到60%和70%以上,平均每日最大致死量可达40头烟粉虱若虫。该蜂对两种生物型烟粉虱的功能反应曲线符合HollingII型,随寄主密度的增加对烟粉虱若虫的寄生和致死数量均增加直至达到每日最大致死数量,而寄生率和致死率则随寄主密度的增加而显著下降。该蜂对两种生物型烟粉虱的功能反应没有显著的差异。     

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

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

新型双向传导杀虫剂—螺虫乙酯对Q型烟粉虱的防治效果

为了筛选出防治Q型烟粉虱的有效药剂,研究了22.4%螺虫乙酯悬浮剂不同浓度、不同施药时间对烟粉虱卵、若虫的防治效果。螺虫乙酯和对照药阿维菌素均对Q型烟粉虱卵无效,螺虫乙酯对若虫具有非常高的杀虫活性,无论在卵期施药、若虫低龄期施药还是高龄期施药,防效均达95%以上,和对照药阿维菌素的防效无显著性差异。施药后20d接虫,防效大幅降低到21.6%以下,施药30d后接虫对若虫无效。根据烟粉虱的发育历期推算,表明螺虫乙酯持效期可达30d。     

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.     

蜡蚧轮枝菌(Lecanicillium lecanii)Bj085-1菌株对烟粉虱的毒力测定

蜡蚧轮枝菌(Lecanicillium lecanii)Bj085-1菌株分生孢子配成1.1×104～1.1×108孢子/mL的5个处理浓度,以京郊尚未喷药的温室采集的烟粉虱(Bemisia tabaci)为试材,采用点滴法对其2龄若虫进行室内毒力测定。结果表明,浓度为1.1×104孢子/mL的Bj085-1分生孢子对烟粉虱若虫的LT50为11.568 d,且随浓度增加其杀虫速度加快。浓度增至1.1×106孢子/mL时,杀虫速度最快,尔后,随着浓度增加速度又有所下降。此外,将Bj085-1菌株经大米培养基培养所得分生孢子配成1.1×107孢子/mL的处理浓度,分2次(间隔7 d)对田间置于纱笼罩栽植的清洁番茄苗上3个不同虫口密度的烟粉虱若虫进行低量喷施防治试验。结果表明,Bj085-1菌株对室外笼罩中的烟粉虱也具有较好的防治效果。     

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。     

Preference of whitefly, Bemisia tabaci, towards black gram genotypes: Role of morphological leaf characteristics

Considering that certain morphological leaf characteristics and foliar pubescence may affect insect feeding preference on plant genotypes, the present studies were undertaken to study the variation in leaf morphology and to further evaluate the influence of leaf characteristics in imparting resistance to black gram (Vigna mungo (L.) Hepper) genotypes against Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Evaluation of nine black gram genotypes against B. tabaci in multiple-choice test revealed that moderately resistant genotypes KU 99-20 and NDU 5-7 recorded significantly lowest whitefly population (egg, nymph and adult) as compared to the susceptible genotypes IPU 02-043, KU 7-602, KU 7-605, KU 7-618 and Mash 1-1 and highly susceptible genotypes KU 7-504 and KU 7-505. Evidence for morphological leaf characteristics was gathered using data from leaf area meter, fluorescent, electron microscopy as well as direct visual observations. Correlations between morphological leaf characteristics of black gram genotypes and the whitefly population were examined. Leaf area, lamina thickness and trichome length were significantly and positively correlated with whitefly eggs, nymphs and adults whereas trichome density and angle were negatively correlated. Thus, black gram genotypes with narrow, thin and highly pubescent leaves having short, but erect trichomes should be selected for developing black gram varieties resistant to whitefly.     

Insecticide resistance in Egyptian populations of the cotton whitefly,Bemisia tabaci (Hemiptera: Aleyrodidae)

Three collections of Bemisia tabaci were taken from cotton and vegetable crops at the beginning of the growing season in Egypt. These displayed marked resistance to the carbamates carbosulfan (ca 20- to 50-fold) and aldicarb (ca 40- to 80-fold) and moderate resistance to the pyrethroids cypermethrin (ca 10- to 30-fold) and lambda-cyhalothrin (ca 10- to 25-fold). They displayed no resistance to the organophosphates profenofos and pirimiphos-methyl, or to imidacloprid. Another population, collected at the end of the growing season, differed markedly in its response. In this population, resistance to carbosulfan remained high (ca 40-fold), resistance to profenofos and cypermethrin was increased (ca 20- and 50-fold respectively) and a slight resistance to imidacloprid was detected (ca 6-fold). Resistance to cypermethrin and profenofos was shown to be similar among adults and nymphs. Irrespective of collection date, none of the populations showed resistance to pyriproxyfen. These Egyptian populations were compared with two representative Israeli populations. The differences between their resistance profiles is discussed in terms of their collection date, their geographical proximity and the patterns of insecticide use at their sites of collection.     

不同培养基继代培养蜡蚧轮枝菌对产孢量和烟粉虱毒力的影响

为了探究不同培养基继代培养的蜡蚧轮枝菌对烟粉虱的作用效果,通过继代培养方法测定JMC-01、JMC-02菌株的产孢量、对烟粉虱的毒力及其几丁质酶活性。结果表明,JMC-01、JMC-02菌株在添加蝉蜕和烟粉虱的PDA培养基中连续培养5代的产孢量、对烟粉虱的毒力、几丁质酶活性均高于无添加的PDA培养基,且JMC-01菌株的各项参数均高于JMC-02菌株。JMC-01菌株在添加蝉蜕的PDA培养基中T_1和T_3代的产孢量最大,均为1.279×10~7个/mL,T_3代对烟粉虱的毒力最大,为88.33%,T_5代的几丁质酶活最高,为0.268 3 U/mL;在添加烟粉虱的PDA培养基中,JMC-01菌株的最大产孢量、对烟粉虱的最高毒力和最高几丁质酶活分别出现在S_2、S_4和S_5代,分别为1.270×10~7个/mL、88.33%和0.325 4 U/mL。回归分析结果显示,JMC-01、JMC-02菌株几丁质酶活性与烟粉虱校正死亡率呈显著的正相关,且拟合优度较好。本试验表明JMC-01、JMC-02菌株均对烟粉虱具有较强的毒力,添加蝉蜕和烟粉虱的培养基可以维持菌株生长特性、增加产孢量、延缓菌株退化、增强菌株的几丁质酶活性,为烟粉虱的生物防治提供了新的菌种资源。     

Evaluation of the entomopathogenic nematode Steinernema feltiae as a biological control agent of the whitefly,Bemisia tabaci

We evaluated the potential for using infective juveniles of the entomopathogenic nematode Steinernema feltiae to control the sweetpotato whitefly Bemisia tabaci B biotype on cucumber, hibiscus, and collard, under greenhouse conditions. The effects of four adjuvants (PVA, glycerol, Triton X-100, and horticultural spraying oil) on the efficiency of Steinernema feltiae in B. tabaci control were also assessed because they might increase nematode survival by reducing desiccation. The mortality of B. tabaci nymphs increased by 18, 18, and 20% on collard, hibiscus, and cucumber plants when S. feltiae concentration increased from 5000 to 15,000 infective juveniles/mL. When treated with S. feltiae (10000 infective juveniles/mL), second instar nymphs suffered greater mortality than the other instars of B. tabaci, regardless of host plant species. Mortality of B. tabaci nymphs was higher on hibiscus than on collard and cucumber plants. The use of adjuvants greatly increased infection of B. tabaci by S. feltiae. The combination of S. feltiae (10,000 infective juveniles/mL) and 1% horticultural spraying oil increased the mortality of second instar B. tabaci nymphs to 86% on collard and 90% on hibiscus, while the combination of S. feltiae and 0.1% Triton X-100 caused 83% mortality on collard and 89% on hibiscus. The potential for incorporating S. feltiae and the adjuvants in B. tabaci management is discussed.