The longevity effects of trehalulose feeding by parasitoids

Abstract.  Insects, particularly phloem-feeding Sternorrhyncha, are known to produce sugars in their honeydew (excreta) that are not found in their host plants. Of these, Bemisia tabaci , the sweet potato whitefly, is the only insect known to produce trehalulose [α- d -glucose (1,1) d -fructose] as a major component of its honeydew. The present study aims to determine whether trehalulose is comparable to sucrose as a nutrient source for three whitefly parasitoids ( Encarsia formosa , Encarsia pergandiella and Eretmocerus eremicus ). In addition, the study also examines trehalulose feeding effects on longevity for a parasitoid of muscoid Diptera, Nasonia vitripennis . Parasitoids are provided diets of either sucrose or trehalulose in varying concentrations (from 0.1% to 70%) or a water control. Sucrose and trehalulose are not significantly different in affecting survival when compared at the same concentration. This was true for all Bemisia parasitoids and N. vitripennis. Certain specific diets are significantly different in pairwise combination tests. There is a significant effect of species, diet type and the interaction of these two factors on the longevity of the three different Bemisia parasitoid species; however, within species, there is no significant increase in longevity observed for either carbohydrate diet. This result contrasts with expectations for the effects of host-modified carbohydrates on longevity. The implications are that, although carbohydrate feeding is essential for these parasitoids, these host-provided sources of carbohydrates are equally capable of extending longevity.     

Distinct sucrose isomerases catalyze trehalulose synthesis in whiteflies,Bemisia argentifolii,and Erwinia rhapontici

Isomaltulose [alpha-D-glucopyranosyl-(1,6)-D-fructofuranose] and trehalulose [alpha-D-glucopyranosyl-(1,1)-D-fructofuranose] are commercially valuable sucrose-substitutes that are produced in several microorganisms by the palI gene product, a sucrose isomerase. Trehalulose also occurs in the silverleaf whitefly, Bemisia argentifoli, as the major carbohydrate in the insect's honeydew. To determine if the enzyme that synthesizes trehalulose in whiteflies was similar to the well-characterized sucrose isomerase from microbial sources, the properties of the enzymes from whiteflies and the bacterium, Erwinia rhapontici, were compared. Partial purification of both enzymes showed that the enzyme from whiteflies was a 116 kD membrane-associated polypeptide, in contrast to the enzyme from E. rhapontici, which was soluble and 66 kD. The enzyme from E. rhapontici converted sucrose to isomaltulose and trehalulose in a 5:1 ratio, whereas the enzyme from whiteflies produced only trehalulose. Unlike the E. rhapontici enzyme, the whitefly enzyme did not convert isomaltulose to trehalulose, but both enzymes catalyzed the transfer of fructose to trehalulose using sucrose as the glucosyl donor. The results indicate that trehalulose synthase from whiteflies is structurally and functionally distinct from the sucrose isomerases described in bacteria. The whitefly enzyme is the first reported case of an enzyme that converts sucrose to exclusively trehalulose.     

甘蓝与黄瓜寄主上B型烟粉虱和温室白粉虱蜜露糖分、氨基酸和挥发物组分的比较分析

粉虱蜜露是粉虱寄生性天敌搜索寄主的主要利它素源。应用离子色谱分别对甘蓝与黄瓜上B型烟粉虱(Bemisia tabaci B-biotype)蜜露以及黄瓜上温室白粉虱Trialeurodes vaporariorum蜜露的接触性利它素糖和氨基酸组分和含量进行了比较研究。结果表明：2种粉虱在不同寄主植物上的蜜露均富含糖和氨基酸,其中糖含量占绝对优势,甘蓝上B型烟粉虱蜜露、黄瓜上B型烟粉虱蜜露和黄瓜上温室白粉虱蜜露中的糖含量分别是相应氨基酸含量的42.5、2.6和5.4倍,其中糖类物质中又以寡糖含量占绝对优势,分别占89.3%、81.7%和88.2%。不同寄主植物和粉虱种类显著影响蜜露中糖和氨基酸的组成和含量。其中,甘蓝上B型烟粉虱蜜露中的寡糖以二糖占优势,占97.3%;二糖中又以蔗糖异构糖和松二糖占优势,分别占52.7%和35.4%。黄瓜上B型烟粉虱蜜露和温室白粉虱蜜露寡糖中以三糖和四糖占优势,分别占73.1%和85.4%;优势糖水苏（四）糖和松三糖分别占40.3%和 26.2%及49.9%和27.0%。甘蓝上B型烟粉虱蜜露中氨基酸以丙氨酸占优势,含量为66.5%;而黄瓜上B型烟粉虱及温室白粉虱蜜露中氨基酸以甘氨酸含量最高,分别占氨基酸总量的38.2%和51.7%。应用GC-MS对甘蓝上B型烟粉虱蜜露和黄瓜上温室白粉虱蜜露挥发物组分的鉴定结果显示,两种粉虱蜜露中共同含有的主要挥发物为邻苯二甲酸二（2-乙基）己酯。     

Microorganisms influence the composition of honeydew produced by the silverleaf whitefly, Bemisia argentifolii

Sugars in the honeydew produced by the silverleaf whitefly, Bemisia argentifolii, and in fermentation of sucrose using homogenates of these insects were analyzed by high performance liquid chromatography. Results suggest that the unusual disaccharide, trehalulose, found in large quantity in honeydew of B. argentifolii, is produced by obligate intracellular microorganisms residing in this insect's mycetomes. Some larger oligosaccharides in this honeydew may be produced by certain Bacillus spp. residing in or on the insects but these bacteria are not involved in an obligate relationship with the whitefly.     

Effect of Bemisia tabaci honeydew and its carbohydrates on search time and parasitization of Encarsia bimaculata

Abstract:  The search time of Encarsia bimaculata Heraty et Polaszek was examined and recorded by using filter paper discs in Petri dish arenas impregnated with Bemisia tabaci (Gennadius) honeydew or its component carbohydrates. Our data show that E. bimaculata used honeydew as a contact kairomone to locate its host. Females responded quantitatively to the honeydew and the search time in the treated patches increased. This increase was concentration-dependent with regard to the amount of honeydew applied, but it levelled off 0.05 g/ml onwards. The response of E. bimaculata to honeydew decreased with increasing time after application and was significantly reduced 8 days after treatment. The parasitoid females were also arrested in patches treated with glucose, fructose, trehalulose and trehalose; trehalose elicited the highest response in the parasitoids. However, sucrose and low concentrations of melezitose did not elicit a significant effect. Glucose, sucrose, fructose, trehalose and trehalulose increased the longevity of the parasitoid females by a factor of 8.4, 8.1, 6.3, 6.1 and 4.2, respectively. Melezitose and 0.15 g/ml natural honeydew, however, had no effect on parasitoid lifespan. The effects of aqueous spray of honeydew sugars on egg to adult survivorship and parasitization of B. tabaci by E. bimaculata significantly differed when compared with controls only in cases where mixtures of glucose + fructose and trehalose and fructose + trehalose were applied.     

Preinfestations of tomato plants by whiteflies (Bemisia tabaci) or aphids (Macrosiphum euphorbiae) induce variable resistance or susceptibility responses

In addition to constitutive plant resistance against pests or pathogens, plants can activate protective mechanisms upon contact with an invader or a chemical elicitor. Studies on induced plant resistance to herbivores, especially piercing-sucking insects, are less abundant than those devoted to pathogens. Several experiments under controlled conditions have been conducted to demonstrate that infestations by Macrosiphum euphorbiae induce plant resistance to Bemisia tabaci in susceptible tomato plants. After three days of exposure to 20 apterous adult aphids, the plants acquired a transiently induced resistance to B. tabaci when aphid removal occurred one or 18 hours prior to B. tabaci infestation; the effect disappeared when four days passed between aphid and whitefly infestations. The resistance observed was both locally and systemically induced. Other assays were performed to evaluate the effect of preinfestation with ten adults of B. tabaci during 48 h on the tomato responses to two different clones (Sp and Nt) of M. euphorbiae. The numbers of nymph and adult aphids were counted after the same time interval as the pre-reproductive period and 20 (Sp clone) or 22 (Nt clone) days after adult aphid removal. The tomato responses induced by whitefly feeding depend on the aphid clone. For the Sp clone, the number of aphid nymphs ten days after adult removal was significantly higher on whitefly preinfested plants than on uninfested plants. However, no significant differences were observed when the aphid clone Nt was tested. The duration of plant response to a previous infestation by B. tabaci is apparently limited.     

丽蚜小蜂两个品系寄生行为及对不同寄主植物上烟粉虱的选择性

对丽蚜小蜂两个品系(分别来自北京和美国)寄生烟粉虱的行为和在番茄、黄瓜、甘蓝、茄子及棉花烟粉虱上的发育历期和寄生率进行了研究。结果表明,丽蚜小蜂通过寄主定位、寄主检查、产卵、清扫和梳理等过程对烟粉虱进行寄生,北京品系平均产卵寄生时间为5.0 m in,美国品系为4.2 m in,品系间差异显著。北京品系在棉花烟粉虱上发育历期最短,为17.4 d,甘蓝烟粉虱上发育历期最长,为20.0 d;美国品系在棉花烟粉虱上发育历期最短,为16.3 d,在其余4种寄主植物烟粉虱上发育历期较长(17.3~17.9 d)。2个品系的寄生率均表现为番茄烟粉虱上最高,分别为37.3%和39.0%;棉花次之,分别为32.2%和35.5%;黄瓜上最低,分别为30.2%和29.6%。在寄主植物选择性试验中,2个品系亦表现为寄生番茄烟粉虱时寄生率最高,美国品系为62.7%,北京品系为56.3%,寄生黄瓜烟粉虱时寄生率最低,分别为30.8%和29.0%。     

An aphid-borne bacterium allied to the secondary symbionts of whitefly

Bacterial 16S rDNA amplified by PCR from the pea aphid Acyrthosiphon pisum included a sequence with >98% similarity to secondary symbionts in the whitefly Bemisia tabaci. The 'pea aphid Bemisia-like bacterium' (PABS) and B. tabaci secondary symbionts are estimated to have diverged 17-34 million years ago, a time considerably more recent than the common ancestor of aphids and whitefly and suggestive of horizontal transmission of this bacterial lineage. PABS was scored in both the gut and ovaries of aphids by PCR and identified as a small rod by in situ hybridisation. PABS was not universal in pea aphids: 2/3 laboratory strains and 13/35 of field aphids were PABS-positive. It is suggested that the incidence of PABS in pea aphids is determined by the balance between loss (processes may include occasional failure of vertical transmission and selection against PABS-positive aphids) and horizontal transfer between insects.     

Wolbachia infections of the whitefly Bemisia tabaci

We report the first systematic survey for the presence of Wolbachia endosymbionts in aphids and whiteflies, particularly different populations and biotypes of Bemisia tabaci. Additional agriculturally important species included were predator species, leafhoppers, and lepidopterans. We used a polymerase chain reaction (PCR)-based detection assay with ribosomal 16S rDNA and Wolbachia cell surface protein (wsp) gene primers. Wolbachia were detected in a number of whitefly populations and species, whitefly predators, and one leafhopper species; however, none of the aphid species tested were found infected. Single, double, and triple infections were detected in some of the B. tabaci populations. PCR and phylogenetic analysis of wsp gene sequences indicated that all Wolbachia strains found belong to group B. Topologies of the optimal tree derived by maximum likelihood (ML) and a ML tree in which Wolbachia sequences from B. tabaci are constrained to be monophyletic are significantly different. Our results indicate that there have been at least four independent Wolbachia infection events in B. tabaci. The importance of the presence of Wolbachia infections in B. tabaci is discussed.     

Assessment of Potential Sublethal Effects of Various Insecticides on Key Biological Traits of The Tobacco Whitefly,Bemisia tabaci

The tobacco whitefly Bemisia tabaci is one of the most devastating pests worldwide. Current management of B. tabaci relies upon the frequent applications of insecticides. In addition to direct mortality by typical acute toxicity (lethal effect), insecticides may also impair various key biological traits of the exposed insects through physiological and behavioral sublethal effects. Identifying and characterizing such effects could be crucial for understanding the global effects of insecticides on the pest and therefore for optimizing its management in the crops. We assessed the effects of sublethal and low-lethal concentrations of four widely used insecticides on the fecundity, honeydew excretion and feeding behavior of B. tabaci adults. The probing activity of the whiteflies feeding on treated cotton seedlings was recorded by an Electrical Penetration Graph (EPG). The results showed that imidacloprid and bifenthrin caused a reduction in phloem feeding even at sublethal concentrations. In addition, the honeydew excretions and fecundity levels of adults feeding on leaf discs treated with these concentrations were significantly lower than the untreated ones. While, sublethal concentrations of chlorpyrifos and carbosulfan did not affect feeding behavior, honeydew excretion and fecundity of the whitefly. We demonstrated an antifeedant effect of the imidacloprid and bifenthrin on B. tabaci, whereas behavioral changes in adults feeding on leaves treated with chlorpyrifos and carbosulfan were more likely caused by the direct effects of the insecticides on the insects'' nervous system itself. Our results show that aside from the lethal effect, the sublethal concentration of imidacloprid and bifenthrin impairs the phloem feeding, i.e. the most important feeding trait in a plant protection perspective. Indeed, this antifeedant property would give these insecticides potential to control insect pests indirectly. Therefore, the behavioral effects of sublethal concentrations of imidacloprid and bifenthrin may play an important role in the control of whitefly pests by increasing the toxicity persistence in treated crops.     

Effect of the alpha-glucosidase inhibitor, bromoconduritol, on carbohydrate metabolism in the silverleaf whitefly, Bemisia argentifolii

The involvement of alpha-glucosidase in the partitioning of ingested sucrose between excretion and incorporation was investigated in the silverleaf whitefly (Bemisia argentifolii). Approximately half of the alpha-glucosidase activity in adult whiteflies was soluble and the remainder was associated with membranes. In contrast, almost all of the trehalulose synthase was membrane-associated. Isoelectric focusing revealed that soluble and membrane-associated alpha-glucosidases were each composed of several isozymes in the pH 5 to 6.5 range, but the distribution of activity among the various isozymes was different. Bromoconduritol, an inhibitor of glucosidases, inhibited trehalulose synthase and alpha-glucosidase activities in whitefly extracts. Inhibition was greatest when bromoconduritol was incubated with extracts prior to the addition of sucrose, consistent with the irreversible nature of this inhibitor. Addition of bromoconduritol to artificial diets decreased the extractable trehalulose synthase and alpha-glucosidase activities by about 30 and 50%, respectively. Ingestion of bromoconduritol reduced the amount of carbohydrate excreted by about 80% without changing the distribution of the major honeydew sugars or causing an increase in the proportion of sucrose that was excreted. Ingestion of bromoconduritol did not affect respiration, the content and distribution of soluble carbohydrates in whitefly bodies, or the conversion of labeled sucrose into glucose, trehalose and isobemisiose. The results indicate that partitioning of ingested carbon between excretion and metabolism in whiteflies is highly regulated, probably involving multiple forms of alpha-glucosidase that facilitate a separation of the processes involved in the metabolic utilization of sucrose from those involved in excretion of excess carbohydrate. Arch. Insect Biochem. Physiol. 45:117-128, 2000. Published 2001 Wiley-Liss, Inc.     

High Performance Liquid Chromatography Analysis of Carbohydrates of Cotton-Phloem Sap and of Honeydew Produced by Bemisia tabaci Feeding on Cotton

Phloem sap from cotton (Gossypium hirsutum L.) was collected from young and mature leaves by the aphid-stylet technique. Exudate was analyzed for carbohydrates by HPLC using sensitive pulsed amperometric detection. The predominant carbohydrate present (>90%) was identified as sucrose. A second, unidentified compound that was not one of the more commonly translocated sugars was detected in mature leaves. Carbohydrates in honeydew produced by the sweet-potato whitefly (Bemisia tabaci [Genn.]) feeding on cotton were sucrose, glucose, fructose, trehalulose, and a series of oligosaccharides.     

Extraordinary resistance to insecticides reveals exotic Q biotype of Bemisia tabaci in the New World

A strain of the whitefly Bemisia tabaci (Gennadius) possessing unusually high levels of resistance to a wide range of insecticides was discovered in 2004 in the course of routine resistance monitoring in Arizona. The multiply resistant insects, collected from poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants purchased at a retail store in Tucson, were subjected to biotype analysis in three laboratories. Polyacrylamide gel electrophoresis of naphthyl esterases and sequencing of the mitochondrial cytochrome oxidase I gene (780 bp) confirmed the first detection of the Q biotype of B. tabaci in the New World. This U.S. Q biotype strain, referred to as Poinsettia'04, was highly resistant to two selective insect growth regulators, pyriproxyfen and buprofezin, and to mixtures of fenpropathrin and acephate. It was also unusually low in susceptibility to the neonicotinoid insecticides imidacloprid, acetamiprid, and thiamethoxam, relative to B biotype whiteflies. In 100 collections of whiteflies made in Arizona cotton (Gossypium spp.), vegetable, and melon (Cucumis melo L.) fields from 2001 to 2005, no Q biotypes were detected. Regions of the United States that were severely impacted by the introduction of the B biotype of B. tabaci in the 1980s would be well advised to promote measures that limit movement of the Q biotype from controlled environments into field systems and to formulate alternatives for managing this multiply-resistant biotype, in the event that it becomes more widely distributed.     

Ecdysteroids and juvenile hormones of whiteflies, important insect vectors for plant viruses

Ecdysteroids and juvenile hormones (JHs) regulate many physiological events throughout the insect life cycle, including molting, metamorphosis, ecdysis, diapause, reproduction, and behavior. Fluctuation of whitefly ecdysteroid levels and the identity of the whitefly molting hormone (20-hydroxyecdysone) have only been reported within the last few years. An ecdysteroid commitment peak that is associated with the reprogramming of tissues for a metamorphic molt in many holometabolous and some hemimetabolous insect species was not observed in last nymphal instars of either the sweet potato whitefly, Bemisia tabaci (Biotype B), or the greenhouse whitefly, Trialeurodes vaporariorum. Ecdysteroids reach peak levels 1-2 days prior to the initiation of the nymphal-adult metamorphic molt. Adult eye and wing differentiation which signal the onset of this molt begin earlier in 4th instar T. vaporariorum (Stages 4 and 5, respectively) than in B. tabaci (Stage 6), and the premolt peak is 3-4 times greater in B. tabaci ( approximately 400 fg/microg protein) than in T. vaporariorum ( approximately 120 fg/microg protein). The JH of B. tabaci nymphs and eggs was found to be JH III, supporting the view that JHs I and II are, with rare exception, only present in lepidopteran insects. In B. tabaci eggs, JH levels were approximately 10 times greater on day 2/3 (0.44 fg/egg or 0.54 ng/g) than on day 5 (0.04 fg/egg or 0.054 ng/g) post-oviposition. Approximately, 1.4 fg/2nd-3rd instar nymph (0.36 ng/g) was detected. It is probable that the relatively high level of JH in day 2/3 eggs is associated with the differentiation of various whitefly tissues during embryonic development.     

Nutritional ecology of a parasitic wasp: food source affects gustatory response, metabolic utilization, and survivorship

The success of biological control is partly mediated by the longevity and reproductive success of beneficial insects. Availability of nectar and honeydew can improve the nutrition of parasitic insects, and thereby increase their longevity and realized fecundity. The egg parasitoid, Anaphes iole, showed strong gustatory perception of trehalulose, a carbohydrate found in homopteran honeydew. Chromatographic analysis demonstrated that enzymatic hydrolysis of sucrose, a common nectar sugar, proceeded at a faster rate than that of melezitose, a sugar common in aphid honeydew. A long-term bioassay showed that longevity was greater at 20 °C than at 27 °C, and at both temperatures survival was generally greatest for wasps provisioned with the three major nectar sugars, sucrose, glucose, and fructose. Patterns of food acceptance and utilization showed that A. iole accepted and utilized a broad range of sugars found in nature, including those found in nectar as well as honeydew. Glucose, fructose, and several oligosaccharides composed of these monosaccharide units appear to be more suitable for A. iole than other sugars tested. Evidence suggests that individual fitness benefits afforded by food sources are important for a time-limited parasitoid, and that continued investigations on the interface between nutrition and biological control are warranted for A. iole.     

Feeding preference of Macrolophus caliginosus (Heteroptera: Miridae) on Bemisia tabaci and Trialeurodes vaporariorum (Homoptera: Aleyrodidae)

A study of predation choices of Macrolophus caliginosus Wagner (Heteroptera: Miridae) late instars and adults, when offered various developmental stages (eggs and nymphs) of the recently established whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was made based on two preference indices. In addition, prey choices of late instars when presented with three ratios of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae) and B. tabaci at a similar developmental stage (eggs, young or late instars) were assessed. M. caliginosus preferred older nymphs of B. tabaci than any other stage. It also chose T. vaporariorum over B. tabaci, unless the latter consisted of > 75% of the available prey. These results suggested that M. caliginosus might interfere with parasitoids such as Encarsia, Eretmocerus, or Amitus spp. because all three species emerge from the host pupal case. Furthermore, in mixed infestations, M. caliginosus preference for T. vaporariorum might either negatively affect the control of B. tabaci, or, contrarily, enhance the predator population, before a B. tabaci outbreak occurs in the greenhouse.     

Plant nitrogen status rapidly alters amino acid metabolism and excretion in Bemisia tabaci

The effect of plant nitrogen (N) status on the content and distribution of free amino acids in the bodies and honeydew of silverleaf whiteflies Bemisia tabaci (Gennadius) Biotype B (= B. argentifolii Bellows and Perring) was determined. Whiteflies fed for 4 days on cotton leaves that received high or low N fertility. For low-N plants, photosynthesis and leaf total N levels were decreased, and a much-reduced amount of free amino acids was recovered in phloem sap. Low N fertility did not affect whitefly total N content, but did markedly decrease the free amino acid content. Glutamine, alanine and proline accounted for over half of the insect free amino acid pool for both N treatments. On a relative basis, adjustments in glutamine levels in response to plant N status were much larger compared to the other amino acids. Large amounts of amino N, especially asparagine, were excreted from whiteflies fed on high-N plants whereas amino N excretion essentially ceased for whiteflies fed on low N plants. The distribution of amino acids in the insects and honeydew was not closely related to the phloem sap amino acids. However, total amino acid excretion was quite indicative of the plant N status and the quality of the insect diet. The results indicated that whitefly free amino acid pools and excretion of amino N were rapidly altered by plant N status.     

Identification and localization of a Rickettsia sp. in Bemisia tabaci (Homoptera: Aleyrodidae)

Whiteflies (Homoptera: Aleyrodidae) are sap-sucking insects that harbor "Candidatus Portiera aleyrodidarum," an obligatory symbiotic bacterium which is housed in a special organ called the bacteriome. These insects are also home for a diverse facultative microbial community which may include Hamiltonella, Arsenophonus, Fritchea, Wolbachia, and Cardinium spp. In this study, the bacteria associated with a B biotype of the sweet potato whitefly Bemisia tabaci were characterized using molecular fingerprinting techniques, and a Rickettsia sp. was detected for the first time in this insect family. Rickettsia sp. distribution, transmission and localization were studied using PCR and fluorescence in situ hybridizations (FISH). Rickettsia was found in all 20 Israeli B. tabaci populations screened but not in all individuals within each population. A FISH analysis of B. tabaci eggs, nymphs, and adults revealed a unique concentration of Rickettsia around the gut and follicle cells, as well as a random distribution in the hemolymph. We postulate that the Rickettsia enters the oocyte together with the bacteriocytes, leaves these symbiont-housing cells when the egg is laid, multiplies and spreads throughout the egg during embryogenesis and, subsequently, disperses throughout the body of the hatching nymph, excluding the bacteriomes. Although the role Rickettsia plays in the biology of the whitefly is currently unknown, the vertical transmission on the one hand and the partial within-population infection on the other suggest a phenotype that is advantageous under certain conditions but may be deleterious enough to prevent fixation under others.     

辽宁省冬季温室内越冬粉虱伪蛹的种类鉴定及烟粉虱体内番茄黄化曲叶病毒的检测

为了揭示辽宁省冬季温室内越冬粉虱伪蛹的种类及烟粉虱Bemisia tabaci （Gennadius）携带番茄黄化曲叶病毒（tomato yellow leaf curl virus, TYLCV）情况, 于2012年1月份在辽宁省不同县市区的温室作物上采集了17份粉虱伪蛹样品（每样品含30头粉虱伪蛹） , 镜检鉴别粉虱种类并利用mtCOI基因对烟粉虱生物型进行了鉴定; 检测了烟粉虱携带TYLCV情况并对其PCR扩增产物进行了测序分析。结 果表明： 辽宁省冬季温室内存在越冬温室白粉虱Trialeurodes vaporariorum （Westwood）与烟粉虱。17份粉虱样品中, 11份样品为烟 粉虱样品, 6份样品为温室白粉虱和烟粉虱混合样品。混合样品中, 温室白粉虱仅在锦州凌海（LH）样品中占优势。17份烟粉虱样品（包 括混合样品）中, 仅有4份样品为B型与Q型混合样品, 其他13份样品烟粉虱生物型均为Q型。17份烟粉虱样品中有3份Q型烟粉虱样品检测 到TYLCV, 系统树分析进一步证实该病毒是TYLCV。调查结果为辽宁省粉虱与TYLCV的早期测报和防控提供了科学依据。     

Toxicity of sucrose octanoate to egg, nymphal, and adult Bemisia tabaci (Hemiptera: Aleyrodidae) using a novel plant-based bioassay

The sweetpotato whitefly, Bemisia tabaci (Gennadius), B biotype, presents a unique problem for vegetable growers by serving as a vector of plant viruses and by inducing physiological disorders of leaves and fruit. An action threshold of a single whitefly is necessary because of the threat of disease in many areas and growers rely heavily on a single class of insecticides (neonicotinoids) for whitefly control. Additional control methods are needed to manage this pest in commercial vegetables. Extracts of wild tobacco contain natural sugar esters that have previously been shown effective in controlling many soft-bodied insects. We developed a novel tomato leaf bioassay system to assess a synthetic sugar ester derivative, sucrose octanoate, for insecticidal activity against the eggs, nymphs, and adults of B. tabaci. The LC50 values for sucrose octanoate against adults, second instars, and fourth instars of the whitefly were 880, 686, and 1,571 ppm, respectively. The LC50 against whitefly eggs was higher (11,446 ppm) but indicated that some egg mortality occurred at the recommended application rate of 0.8-1.2% (3,200-4,800 ppm [Al]). Toxicity of sugar esters to whitefly eggs has not been reported previously. The tomato leaf bioassay produced reliable and repeatable results for whitefly toxicity studies and predicted that effective nymph and adult whitefly control can be achieved with sucrose octanoate at application rates < or = 1% (4,000 ppm [AI]). Field efficacy studies are warranted to determine whether this biorational pesticide has application in commercial tomato production.