Analysis of resistance in tomato and sweet pepper against the greenhouse whitefly using electrically monitored and visually observed probing and feeding behaviour

Different types of plant resistance against the greenhouse whitefly, Trialeurodes vaporariorum, were distinguished according to the tissue location of the resistance factors. The effects of resistance factors were compared by measuring the electrically monitored and visually observed probing and feeding behaviour of whiteflies on two resistant tomato genotypes (82207 and 82216), a susceptible tomato cultivar, and a non-host plant, sweet pepper. On sweet pepper, whiteflies displayed very short first probes, very long pathway probing and spent much time on non-feeding activities such as walking and standing still. Also, a high percentage of whiteflies rejected sweet pepper without ingesting substances from the phloem vessel. These data suggest a strong resistance that is based on the factors present in surface/epidermis and/or mesophyll layers of this plant. The behaviour of whiteflies on tomato 82207 was very different from that on sweet pepper. On tomato 82207 whiteflies apparently did not perceive resistance factors on the leaf surface and in the mesophyll. Resistance factors appeared to be present in the phloem tissue, because a higher number of phloem phases, longer phloem salivation periods and shorter phloem ingestion periods were observed when compared with the susceptible tomato cultivar. Tomato 82216 showed no clear resistance factor in the phloem. The importance of combined EPG and behavioural research for host-plant resistance studies are discussed.     

B型烟粉虱在甘蓝、西葫芦和辣椒上的刺吸取食行为

利用刺吸电波技术（EPG）记录了B型烟粉虱Bemisia tabaci在甘蓝Brassica oleracea L. var. caqitata、西葫芦Cucurbita pepo L.和辣椒Capsicum annuum L.上的刺吸取食波形。结果表明,3种寄主植物的适合度为甘蓝>西葫芦>辣椒。在所观察的25头烟粉虱中,到达甘蓝、西葫芦和辣椒韧皮部的个体数分别为24、19和15,其中持续吸食头数为22、10和1。在第一阶段（从刺吸开始到第一个E(pd)1出现）,烟粉虱在甘蓝、西葫芦和辣椒3种植物上非刺探时间所占比例分别为9.59%、23.55%和36.97%,三者差异显著; 在第二阶段（从第一个E(pd)1出现到第一次韧皮部持续吸食）,烟粉虱在甘蓝和西葫芦上所考察的4个指标无显著差异; 在第三阶段（从第一次韧皮部持续吸食至记录结束）,烟粉虱在甘蓝上第一次韧皮部持续吸食后的刺探次数（4.73）显著低于在西葫芦上的刺探次数（13.40）。在自由状态下,烟粉虱60 min内在甘蓝、西葫芦和辣椒上留存粉虱的百分比分别为100％、88％和28％,这进一步验证了上述依据EPG记录得到的结果。     

Feeding Experience of Bemisia tabaci (Hemiptera: Aleyrodidae) Affects Their Performance on Different Host Plants

The sweetpotato whitefly, Bemisia tabaci biotype B is extremely polyphagous with >600 species of host plants. We hypothesized that previous experience of the whitefly on a given host plant affects their host selection and performance on the plants without previous experience. We investigated the host selection for feeding and oviposition of adults and development and survival of immatures of three host-plant-experienced populations of B. tabaci, namely Bemisia-eggplant, Bemisia-tomato and Bemisia-cucumber, on their experienced host plant and each of the three other plant species (eggplant, tomato, cucumber and pepper) without previous experience. We found that the influence of previous experience of the whiteflies varied among the populations. All populations refused pepper for feeding and oviposition, whereas the Bemisia-cucumber and the Bemisia-eggplant strongly preferred cucumber. Bemisia-tomato did not show strong preference to any of the three host palnts. Development time from egg to adult eclosion varied among the populations, being shortest on eggplant, longest on pepper, and intermediate on tomato and cucumber except for the Bemisia-cucumber developed similarly on tomato and pepper. The survivorship from egg to adult eclosion of all populations was highest on eggplant (80-98%), lowest on pepper (0-20%), and intermediate on tomato and cucumber. In conclusion, the effects of previous experience of whiteflies on host selection for feeding and oviposition, development, and survivorship varied depending on host plants, and host plants play a stronger role than previous experience. Preference of feeding and oviposition by adults may not accurately reflect host suitability of immatures. These results provided important information for understanding whitefly population dynamics and dispersal among different crop systems.     

Difference in feeding behaviors of two invasive whiteflies on host plants with different suitability: implication for competitive displacement

In China, Bemisia tabaci Q (commonly known as biotype Q) has rapidly displaced B (commonly known as biotype B) in the past 6 years. The mechanisms underlying such phenomenon have been studied extensively in recent years; however, we have not come to a definitive conclusion yet. In the present study, the differences in host suitability between B and Q whitefly adults to five host plants (cabbage, cotton, cucumber, poinsettia, and tomato) were evaluated based on their respective feeding behaviors using a direct-current electrical penetration graph (DC-EPG) system. Pair-wise comparisons of B. tabaci B and Q feeding on each of the five host plants clearly indicate that Q feeds better than B on tomato, cotton and poinsettia, while B feeds better than Q on cabbage and cucumber. The EPG parameters related to both phloem and non-phloem phases confirm that cabbage and cucumber are best suited to B, while tomato, cotton, and poinsettia are best suited to Q. Our present results support the contention that host suitability and adult feeding behavior contribute to the competitive displacement of biotype B by biotype Q. The discrepancy between field (previous studies) and laboratory results (this study), however, suggests that 1) whitefly displacement is apparently contributed by multiple factors; and 2) factor(s) other than the host plant suitability may play a vital role in dictating the whitefly biotypes in the field.     

Intraguild predation among plant pests: western flower thrips larvae feed on whitefly crawlers

Omnivores obtain resources from more than one trophic level, and choose their food based on quantity and quality of these resources. For example, omnivores may switch to feeding on plants when prey are scarce. Larvae of the western flower thrips Frankiniella occidentalis Pergande (Thysanoptera: Thripidae) are an example of omnivores that become predatory when the quality of their host plant is low. Western flower thrips larvae usually feed on leaf tissue and on plant pollen, but may also attack eggs of predatory mites, their natural enemies, and eggs of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae), one of their competitors. Here, we present evidence that western flower thrips larvae prey on Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae), another competitor for plant tissue. We tested this on two host plant species, cucumber (Cucumis sativa L.), considered a host plant of high quality for western flower thrips, and sweet pepper (Capsicum annuum L.), a relatively poor quality host. We found that western flower thrips killed and fed especially on whitefly crawlers and that the incidence of feeding did not depend on host-plant species. The developmental rate and oviposition rate of western flower thrips was higher on a diet of cucumber leaves with whitefly crawlers than on cucumber leaves without whitefly crawlers, suggesting that thrips do not just kill whiteflies to reduce competition, but utilize whitefly crawlers as food.     

Analysis by DC–EPG of the resistance to Bemisia tabaci on an Mi-tomato line

The tomato Mi gene confers resistance to nematodes, Meloidogyne spp., and to the potato aphid, Macrosiphum euphorbiae (Thomas). Previous greenhouse choice assays with Bemisia tabaci (Gennadius) showed that tomato commercial varieties carrying this gene had significantly lower values of host suitability and whitefly reproduction than varieties lacking Mi. This indicated that Mi, or another gene in its region, could regulate partial resistance. In order to characterise this resistance, probing and feeding behaviour of Bemisia tabaci B-biotype was studied with DC Electrical Penetration Graph (EPG) technique on the near-isogenic tomato lines Moneymaker (without Mi) and Motelle (carrying Mi). Significant differences (P < 0.05) between tomato lines were found in EPG parameters related to epidermis and/or mesophyll tissues. On Motelle, a lower percentage of whiteflies achieved phloem phase and they made more probes before attaining first phloem phase, had a higher ratio (number of probes before first phloem phase)/(total number of probes), had a longer total duration of non-probing time, and a longer time before making the first intracellular puncture and before making the first phloem phase. In contrast, most of the parameters related to phloem phase were found not to differ significantly between these near-isogenic lines. The behavioural data strongly suggest that the partial resistance in the variety Motelle is due to factors in the epidermis and/or mesophyll that inhibit the whiteflies from reaching phloem sieve elements. However, once the stylets reach a sieve element, whitefly behaviour did not differ between the two varieties. Thus, phloem sap of the two varieties appears to be equally acceptable to the whiteflies. Further studies are necessary to provide a better understanding of these mechanisms of resistance to whiteflies in tomatoes.     

Multitrophic interactions of the silverleaf whitefly,host plants,competing herbivores,and phytopathogens

Our laboratory found that silverleaf whitefly (SLW; Bemisia argentifolii Bellows & Perring) feeding alters host plant physiology and chemistry. The SLW induces a number of host plant defenses, including pathogenesis-related (PR) protein accumulation (e.g., chitinases, beta-1,3-glucanases, peroxidases, chitosanases, etc.). Induction of the PR proteins by SLW feeding occurs in various plant species and varieties. The extent and type of induction is dependent on a number of factors that include host plant growing conditions, the length of time the host plant is exposed to SLW feeding, the plant variety, and SLW population densities. The appearance of PR proteins correlates well with reduced infestations of conspecific insect herbivore competitors. Greenhouse and field experiments in which herbivore competitors (cabbage looper, Trichoplusia ni; leaf miner, Liromyza trifolii) were placed on plants previously exposed to SLW feeding demonstrated behavioral differences (oviposition, feeding preferences) and reduced survival rates and development times of these insects. The interaction was asymmetrical, i.e., SLW infestations of plants previously exposed to leaf miners had little or no effect on SLW behavior (oviposition). Induction of plant-defensive proteins by SLW feeding was both local (at the feeding site) and systemic (uninfested leaves distant to the feeding site). There are interactions between diseases such as tomato mottle virus (ToMoV; a geminivirus) and the host plant and SLW. PR proteins were induced in tomato plants infected with ToMoV much as they were via non-viruliferous SLW feeding. The presence of ToMoV in tomato plants significantly increased the number of eggs produced by SLW females. Experiments using tomato plants, powdery mildew (PM), and tobacco mosaic virus (TMV) show that whitefly infestations can affect plant pathogen relationships but the effects vary among pathogen types. Enzyme analyses prior to pathogen inoculation showed that whitefly treatment significantly increased the activities of foliar chitinase and peroxidase. Evaluation of pathogen growth 3 weeks after inoculation showed that whitefly feeding significantly reduced the incidence of PM. However, TMV levels evaluated by ELISA were not significantly affected by whitefly feeding. Six weeks after inoculation with pathogens, the chitinase and peroxidase activities were still elevated in plants initially fed on by whiteflies but continuing pathogen infection had no effect on these enzymes. The possibility that geminivirus infection and/or SLW infestations isolate the host plant for the selected reproduction of the virus and the insect is discussed. Multitrophic cascade effects may contribute to the successful eruptive appearance of SLW on various crops, ranking them as a major pest. They may explain the general observation that when SLW infest a host plant there are few if any competing insect herbivores and pathogens found in the host. However, the results indicate that certain SLW-virus relationships could be mutualistic.     

烟粉虱传播双生病毒研究进展

综述了烟粉虱Bemisia tabaci对双生病毒的获取、传播及存留等方面的特性。烟粉虱最短的获毒和接种时间为15～30 min;双生病毒在烟粉虱体内可存留1至数周,有的终身存在。烟粉虱对双生病毒的传毒效率除了随其获毒及传毒时间的延长、传毒烟粉虱个体数量的增加以及病毒体浓度的增加而提高外,还与烟粉虱的龄期及性别有关。双生病毒除了在植物与粉虱之间直接传播外,还可通过烟粉虱交配及经卵携带的途径在烟粉虱个体和代别间进行传播。寄主植物、双生病毒的一些特殊蛋白以及烟粉虱内共生菌产生的GroEL蛋白,都可影响烟粉虱携带的双生病毒种类及传毒的可能性。双生病毒可对烟粉虱的发育、存活和生殖产生不利或有利的影响。雌成虫携带番茄黄化曲叶病毒（tomato yellow leaf curl virus, TYLCV）后,存活力和生殖力均下降; 而携带番茄斑驳病毒（tomato mottle virus, ToMoV）后,生殖力提高。此外,植物感染双生病毒后,其对烟粉虱的适合性可能提高。     

THE PROBING AND FEEDING PROCESS OF THE GREENHOUSE WHITEFLY, TRIALEURODES VAPORARIORUM WESTWOOD

Abstract  The preference of greenhouse whiteflies varies with different species of host plants and leaves of different age. They prefer young leaves of tobacco, cucumber, broadbean and cowpea significantly more than the young leaves of paprika and old leaves of broadbean and cowpea. Behavioural studies indicated that the leaf-time and total probing time were significantly longer on preferred leaves than on non-preferred leaves. On non-preferred leaves, probing may continue about 2 minutes but not longer than 5 minutes. On preferred leaves, there were both frequent probing for short intervals and probing (+feeding) which continued for 10 minutes or more. Morphological studies indicated that, in general, it needed 10 to 15 minutes for the stylet to reach the phloem and feed. The probing process takes no more than 10 to 15 minutes. Probing can be divided into test probing which takes less than 2 minutes to reach depths of 20 to 50 pm, and exploratory probing which surpasses 5 minutes. Test probing is the key process for determining host plant selection, and the chemical composition of the leaf surface wax may play an important role.     

Choice of Tethering Material Influences the Magnitude and Significance of Treatment Effects in Whitefly Electrical Penetration Graph Recordings

The electrical penetration graphing or electropenetrography (EPG) technique is essential for understanding interactions of hemipteran insects with their host plants. Typically, 10–12.5 μm diameter gold wire is used as the tethering material in EPG studies. This wire was originally chosen based on suitability for aphids, but application of the EPG technique to other insects necessitates testing of alternative tethering materials that permit natural foraging and probing behavior. Whiteflies are one group for which EPG studies are increasing, with most researchers using 10 or 12.5 μm diameter gold wire even though these insects are smaller than aphids and very different in mobility. However, 2.5 μm diameter Wollaston process platinum wire has been used for a subset of EPG studies and seems to permit more natural movement and feeding behaviors. Here, we compared EPG variables derived from recordings of the sweet potato whitefly (Bemisia tabaci) tethered with 12.5 μm diameter gold wire or 2.5 μm diameter platinum wire. On a suitable host, gold-tethered whiteflies had reduced phloem phases, which are indicative of host plant acceptance, compared to platinum-tethered whiteflies. When we included a treatment known to reduce plant quality (methyl jasmonate application), platinum-tethered whiteflies exhibited expected reductions in EPG variables related to host acceptance, while gold-tethered whiteflies either had no response, or the opposite response. Our results indicate that tethering material strongly influences the outcome of EPG experiments, with important consequences for evaluations of host plant resistance, putative instances of plant virus manipulation, and feeding variables associated with virus transmission.     

Response of the polyphagous whitefly Bemisia tabaci B-biotype (Hemiptera: Aleyrodidae) to crop diversification - influence of multiple sensory stimuli on activity and fecundity

A fundamental question concerning crop diversification is which mechanisms determine pest population size in polycultures compared to monocultures. It has been proposed that polyphagous insects experience a difficulty in decision-making when selecting food and oviposition sites in the presence of different host plants. This hypothesis was tested in the extremely polyphagous whitefly Bemisia tabaci (Gennadius) B-biotype, where behaviour (movement) and fecundity of females were compared in choice and no-choice experiments in the laboratory. Two parallel tests, one on different crops, including cucumber, bean and tomato, and one on different tomato cultivars, were conducted using both a mixture of crops and of tomato cultivars, as opposed to the same crop or cultivar respectively. Bemisia tabaci showed a distinct behavioural preference for cucumber when exposed to different crops simultaneously suggesting that B. tabaci has no difficulty in choosing a host plant, i.e. in making a decision, when one of the plants offered in the choice test is a high-ranking host plant. Conversely, when only low-ranking hosts of similar, but not identical, signatures were present, female whiteflies appeared to have difficulty in making a decision, resulting in increased movement and reduced fecundity. This is consistent with both the hypothesis that polyphagous insects have a problem selecting a host plant when given multiple choices and with the hierarchy threshold model, under which egg loads are lessened between periods of searching for better host plants. The study illustrates how insect behaviour can be affected by inter-cropping not only with different crops, but also with different cultivars of the same crop, thus potentially providing a simple and efficient way of reducing whitefly population build-up.     

B型烟粉虱对23种寄主植物适应度的评估和聚类分析

本文利用前期开发的两个寄主植物适应度评估模型对B型烟粉虱能够完成发育的23种寄主进行了寄主适应度评估,并对评估结果进行了聚类分析,分析结果显示供试烟粉虱种群存在明显的寄主偏好性,黄瓜与甘蓝为嗜好寄主,繁殖力大,若虫成活率高,非常有利于烟粉虱的种群发育;而其它寄主在营养状况、物理性状及次生化合物的综合作用下,烟粉虱的寄主植物适应度变化较大且整体低于嗜好寄主,结果暗示烟粉虱的寄主生态位可能存在从核心到周缘的分层现象。比较了两个评估模型的分析结果,虽然在低层聚类中存在差异,但高层聚类的结果趋于一致。     

Cardinium infection alters cotton defense and detoxification metabolism of its whitefly host

Field monitoring revealed that the infection ratio of the bacterial symbiont Cardinium in the whitefly (Bemisia tabaci MED) was relatively low in northern China. However, the role of this symbiont and the symbiont–whitefly–host plant interaction mechanism are poorly understood. We investigated the influence of Cardinium on the competitiveness of the host whitefly and the physiological interaction between the host plants and host whiteflies. Cardinium-infected whiteflies were displaced by uninfected whiteflies after 5 generations, which showed that Cardinium infection reduced whitefly competitiveness. The defense response genes of cotton significantly decreased under infestation by infected whiteflies compared to uninfected whiteflies. The expression of detoxification metabolism genes, especially the uridine 5ʹ-diphospho-glucuronyltransferase and P450 genes, in infected whiteflies significantly decreased. These results demonstrated that Cardinium could inhibit the defense response of the host plant and decrease the detoxification metabolism ability of the host whitefly. The reduced competitiveness of infected whiteflies may be associated with the inhibition of the whitefly detoxification metabolism by Cardinium, resulting in the reduced performance of infected whiteflies. However, Cardinium infection can suppress plant defenses, which may benefit both infected and uninfected whiteflies when they coexist. This research illustrates the symbiont–whitefly–host plant interaction mechanism and the population dynamics of the whitefly.     

Stylet penetration behavior resulting in inoculation of a semipersistently transmitted closterovirus by the whitefly Bemisia argentifolii

The electrical penetration graph (EPG) technique was used to determine what part of stylet penetration behavior by the whitefly vector, Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae), is lettuce chlorosis virus (LCV) inoculated in the host plant Malva parviflora L. LCV is a semipersistently-transmitted closterovirus. Since closteroviruses generally are found in the phloem of their plant hosts, this study tested the hypothesis that virus inoculation occurs during the phloem phase of stylet penetration behavior. Virus-exposed whiteflies were allowed to feed on uninfected host plants, and the whiteflies were divided into two experimental groups: group 1 attained phloem phase on the uninfected plants, and group 2 did not attain phloem phase. Two series of tests were conducted, one where whiteflies were manipulated so that the amount of time spent in non-phloem phase stylet penetration behaviors was similar between group 1 and group 2, and a second series of tests where whiteflies were manipulated so that the number of intracellular punctures made during stylet penetration was similar between group 1 and group 2. Both series of tests indicated that virus inoculation took place primarily during phloem phase. Considering only individual whiteflies shown to be capable of transmitting virus, 11 of 23 whiteflies (48%) in the phloem phase treatment successfully inoculated the virus whereas only one of 19 whiteflies (5%) in the non-phloem phase treatment successfully inoculated the virus (P=0.00008).     

Root nematode infection enhances leaf defense against whitefly in tomato

The foliar response to different herbivores sharing the same hosts is an important topic for the study of plant-insect interactions. Plants evolve local and systemic resistant strategies to cope with herbivores. Many researchers have characterized the mechanisms of leaf responses to insect infestation; however, the fact that roots serve as systemic resistance modulators to leaf herbivores has been widely ignored. Here, we report that tomato (Solanum lycopersicum) plants infected with southern root-knot nematodes (Meloidogyne incognita)—which feed on the roots to form nodules—enhanced leaf defenses against aboveground attackers, specifically, the whitefly (Bemisia tabaci). Our results show that nematode infection reduced the whitefly population abundance because of conferring a stronger SA-dependent defense pathway against whitefly than in tomato plants without nematode infection. Meanwhile, nematode-infected tomato plant also activated the foliar JA-dependent defense pathway at 4 h after whitefly infestation. However, the foliar JA-dependent defense under whitefly infestation alone was suppressed, with the JA content being nearly 30 % lower than that in tomato plants co-infected with nematodes and whiteflies. Furthermore, nematode infection significantly decreased the plant nitrogen concentration in leaves and roots. As a result, nematode infection reduced the number of whiteflies by enhancing foliar SA-dependent defense, activating JA-dependent defense and decreasing nitrogen nutrition. Our results suggest that underground nematode infection significantly enhances the defense ability of tomato plants against whitefly.     

Vector-virus mutualism accelerates population increase of an invasive whitefly

The relationships between plant viruses, their herbivore vectors and host plants can be beneficial, neutral, or antagonistic, depending on the species involved. This variation in relationships may affect the process of biological invasion and the displacement of indigenous species by invaders when the invasive and indigenous organisms occur with niche overlap but differ in the interactions. The notorious invasive B biotype of the whitefly complex Bemisia tabaci entered China in the late 1990s and is now the predominant or only biotype in many regions of the country. Tobacco curly shoot virus (TbCSV) and Tomato yellow leaf curl China virus (TYLCCNV) are two whitefly-transmitted begomoviruses that have become widespread recently in south China. We compared the performance of the invasive B and indigenous ZHJ1 whitefly biotypes on healthy, TbCSV-infected and TYLCCNV-infected tobacco plants. Compared to its performance on healthy plants, the invasive B biotype increased its fecundity and longevity by 12 and 6 fold when feeding on TbCSV-infected plants, and by 18 and 7 fold when feeding on TYLCCNV-infected plants. Population density of the B biotype on TbCSV- and TYLCCNV-infected plants reached 2 and 13 times that on healthy plants respectively in 56 days. In contrast, the indigenous ZHJ1 performed similarly on healthy and virus-infected plants. Virus-infection status of the whiteflies per se of both biotypes showed limited effects on performance of vectors on cotton, a nonhost plant of the viruses. The indirect mutualism between the B biotype whitefly and these viruses via their host plants, and the apparent lack of such mutualism for the indigenous whitefly, may contribute to the ability of the B whitefly biotype to invade, the displacement of indigenous whiteflies, and the disease pandemics of the viruses associated with this vector.     

How predatory mites find plants with whitefly prey

We investigated the searching behaviour of two species of predatory mites, Typhlodromips swirskii (Athias-Henriot) and Euseius scutalis (Athias-Henriot), both known to feed on immature stages of the whitefly Bemisia tabaci Gennadius. When released in a greenhouse inside a circle of cucumber plants that were alternatingly clean or infested with immature whiteflies, the mites took several days to find plants. Both species were recaptured significantly more on plants with whiteflies. This suggests that the mites are able to discriminate between plants with and without whiteflies. The predators may either have been attracted to plants with whiteflies from a distance or arrested on plants with whiteflies. Typhlodromips swirskii that had previously fed on whitefly immatures on cucumber leaves were significantly attracted by volatiles from cucumber plants with whiteflies in a Y-tube olfactometer. This suggests that the mites use volatile cues to discriminate between infested and clean plants. However, this response waned rapidly; if predators, experienced as above, were starved for 3–4 h in absence of cucumber leaves, they no longer preferred volatiles of infested plants to clean plants. Furthermore, T. swirskii that had no experience with immature whiteflies on cucumber plants also did not prefer odours of infested plants to those of clean plants. Because the release experiment with this species in the greenhouse was done with inexperienced predators, this suggests that the aggregation of mites on plants with whiteflies was mainly caused by differential arrestment of mites on plants with prey and clean plants. For T. swirskii, this was in agreement with the finding that the fraction of predators on plants with prey increased with time to levels higher than 70%. A less clear trend was found for E. scutalis, for which the fraction of predators on plants with prey stabilized soon after release to levels from 54–70%. Hence, the predatory mites may find plants with prey by random searching, but they are subsequently arrested on these plants. An earlier study showed that 87% of all whiteflies released in a set-up as used here were recaptured within 1 day. Hence, the effectiveness with which predatory mites locate plants with whiteflies is low compared with that of their prey. We expect this to generate spatial patterns in the dynamics of predator and prey and this may have consequences for biological control of whiteflies with predatory mites.     

保护地间作芹菜对温室粉虱的防治作用

温室白粉虱Trialeurodes vaporariorum(Westwood)和烟粉虱Bemisia tabaci(Gennadius)是严重危害葫芦科、茄科和豆科等多种蔬菜的主要害虫,具有分布范围广、种群数量大、繁殖力强等特性。作者通过田间试验研究了蔬菜保护地内间作温室粉虱非嗜食植物芹菜(Apium graveliens L.)对其的防治效果。结果表明:与空白处理和常规化学防治相比,在番茄和黄瓜保护地内间作芹菜对温室粉虱均具有显著的防治效果,驱避效果分别达到98.0%和84.5%。这些结果是初步的,但其为进一步研究温室粉虱的寄主选择机制和非化学防治方法提供了依据。     

Host plants influence susceptibility of whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) to the entomopathogenic fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae)

We quantified the tritrophic effect of host plant on the susceptibility of the sweetpotato whitefly Bemisia tabaci (Genn.) to a fungal pathogen in the laboratory. Second-instar whiteflies reared on cucumber, eggplant, tomato and bean plants for six generations were exposed to conidial suspensions of Isaria fumosorosea isolate IF-1106. Our results did not detect differences in response (proportional survival or median lethal time, LT₅₀ days) among insect populations derived from different plants that were treated with 10⁷ conidia/ml. However, at concentrations ≤ 5×10⁶ conidia/ml, whiteflies reared on bean and tomato died significantly more quickly (i.e. LT₅₀ of 4–5 days) compared with cucumber and eggplant reared populations (5–7 days). Bean and tomato-reared populations were also more susceptible to mycosis (LC₅₀ ≈ 6 × 10⁵ conidia/ml) compared with those reared on cucumber (1.9 × 10⁶ conidia/ml) and eggplant (1.5 × 10⁶ conidia/ml). A separate study confirmed that this differential response of whitefly populations to I. fumosorosea was not explained by differences in deposition rate of conidia on leaf surfaces (i.e. a dosage effect). Our findings show that host plants affect the pathogenicity and virulence of a herbivore pathogen, but depend on the rate of exposure (inoculum) applied.     

Effect of geminivirus infection and Bemisia infestation on accumulation of pathogenesis-related proteins in tomato

The whitefly, Bemisia tabaci biotype B, has been shown to cause pathogenesis-related (PR) proteins to accumulate in plants as a result of direct feeding, but their specific role in plant defensive systems is unclear. Our objective was to compare accumulation of tomato PR proteins (beta-1,3-glucanase, chitinase, peroxidase, P2 and P4) in response to whitefly, with or without tomato mottle virus (ToMoV) infection. Tomato PR protein response was measured over time in plants divided into three treatments: uninfected controls (with or without whiteflies) and plants infested with viruliferous (ToMoV) whiteflies. Five- to six-leaf plants were infested with approximately 5 adult whitefly per leaf. Plants were sampled prior to whitefly infestation and at 14, 28, 42, and 56 days. By 56 days, plants infested with viruliferous whiteflies had significantly more eggs (2.5-fold) and nymphs (4.5-fold) than plants with nonviruliferous whiteflies. A significant increase in the enzymatic activity of all measured PR proteins, as compared to control plants, was only seen in viruliferous whitefly-infested plants. No significant difference was observed in enzyme activities between the uninfected control plants either with or without whiteflies. The greatest differences for all PR proteins assayed were observed 42 days after treatment initiation. Protein blot analyses showed that the differences in PR protein activities among the treatments were due to changes in specific enzyme levels within the plant and were associated with concomitant increases in levels of P2 and P4 PR proteins. Under our experimental conditions, it is clear that PR protein response is much more intense when it is attacked by whiteflies carrying ToMoV than by whitefly alone.