Characterization of resistance, evaluation of the attractiveness of plant odors, and effect of leaf color on different onion cultivars to onion thrips (Thysanoptera: Thripidae)

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a worldwide pest of onion, Allium cepa L. In field studies on onion resistance conducted in 2007 and 2008 using 49 cultivars, 11 showed low leaf damage by T. tabaci. In laboratory studies, the 11 cultivars, along with two susceptible checks and four additional cultivars, were evaluated to characterize resistance to T. tabaci and to determine if color and/or light reflectance were associated with resistance to T tabaci. No-choice tests were performed with adults and the numbers of eggs and larvae were counted on each cultivar after three and 10 d, respectively. In choice tests in which all cultivars were planted together in a circle in a single pot, 100 adults were released and the number of adults on each plant was evaluated 24 h later. The behavioral response of walking T. tabaci adults to plant odors was studied in a glass Y-tube olfactometer. The reflectance spectrum of leaves was measured using a UV-VIS spectrophotometer. Results indicate that resistant cultivars showed an intermediate-high antibiotic effect to T. tabaci and all of them showed a very strong antixenotic effect. There were no significant preferences in the response of walking T. tabaci adults to plant odors. The two susceptible cultivars had the highest values of leaf reflectance for the first (275-375 nm) and second (310-410 nm) theoretical photopigment-system of T. tabaci, and these values were significantly different from most resistant cultivars. These results suggest a strong response of T. tabaci to onion cultivars with higher reflectance in the ultraviolet range (270-400 nm). Overall, these results appear promising in helping to identify categories of resistance to T. tabaci in onions that can be used in breeding programs.     

桑蓟马在桑树中空间分布的研究

桑蓟马Pseudodendrothrips mori是桑树的一种主要害虫。它的寄生直接影响供桑叶的质量和产量。我们通过泰勒幂法则和Morisita的散度指标对桑树蓟马在植株和桑园内的空间分布进行检验,结果显示:P.mori种群在植株内和桑园里的分布都存在局部化。桑树中蓟马的分布在树内显示出幼虫蓟马位于低层(从上面叶子起5-10层),但成虫更喜欢上层(从上面叶子起1-5层)。同一植株叶子的不同方向上蓟马密度没有出现明显变化。桑园内蓟马主要分布在桑园东部、南部和北部的植株上,中部,西部植株上的蓟马密度较低。P.mori的成虫和幼虫在叶子上的分布呈现明显聚集化。     

烟粉虱成虫对黄瓜叶龄的喜好性及与后代发育适合度间的关系

在室内采用笼罩和发育测定方法,研究了烟粉虱成虫对黄瓜叶龄的喜好性及其与后代生长发育、存活之间的关系,同时调查了叶毛密度与成虫喜好性之间的相关关系。结果表明(1)烟粉虱成虫比较喜欢在黄瓜植株的中部叶片取食和产卵。(2)叶龄对烟粉虱的存活率没有显著影响,对烟粉虱的发育历期只在卵期和若虫四龄期表现出显著影响,对其他龄期或整个世代均没有显著影响。(3)叶毛密度随着叶龄的增大而顺次显著减小;在接虫初始阶段,烟粉虱成虫的叶片选择性与叶毛密度成显著负相关关系,但72h后具有中等叶毛密度的叶片上的成虫数量和着卵量均显著高于叶毛密度较大或较小的叶片。研究结果对培育抗烟粉虱的黄瓜品种和改进烟粉虱的防治措施具有一定指导意义。     

Impact of straw mulch on populations of onion thrips (Thysanoptera: Thripidae) in onion

Development of insecticide resistance in onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), populations in onion (Allium spp.) fields and the incidence of the T. tabaci transmitted Iris yellow spot virus have stimulated interest in evaluating alternative management tactics. Effects of straw mulch applied in commercial onion fields in muck areas of western New York were assessed in 2006 and 2007 as a possible onion thrips management strategy. In trials in which no insecticides were applied for thrips control, straw mulch-treated plots supported significantly lower T. tabaci populations compared with control plots. In both years, the action thresholds of one or three larvae per leaf were reached in straw mulch treatments between 7 and 14 d later than in the control. Ground predatory fauna, as evaluated by pitfall trapping, was not increased by straw mulch in 2006; however, populations of the common predatory thrips Aeolothrips fasciatus (L.) (Thysanoptera: Aeolothripidae) were significantly lower in straw mulch plots in both years. Interference of straw mulch in the pupation and emergence of T. tabaci was investigated in the lab and their emergence was reduced by 54% compared with bare soil. In the field the overall yield of onions was not affected by the straw mulch treatment; however, the presence of jumbo grade onions (>77 mm) was increased in 2006, but not in 2007. These results indicate that populations of T. tabaci adults and larvae can be significantly reduced by the use of straw mulch without compromising overall onion yield. The use of this cultural practice in an onion integrated pest management program seems promising.     

Diamondback moth oviposition: effects of host plant and herbivory

The oviposition behaviour of Plutella xylostella L. (Lepidoptera: Plutellidae) on Chinese cabbage (Brassica rapa L. Pekinensis, cv. Wombok), canola (Brassica napus L. cv. Thunder TT), and cabbage (Brassica oleracea L. Capitata, cv. sugarloaf) (Brassicaceae) was studied in the laboratory. In no‐choice experiments moths laid most eggs on the stems and lower three leaves of cabbage plants, the lower three leaves of canola plants, but on the upper three leaves of Chinese cabbage plants. The effects of conspecific herbivore damage to foliage could be replicated by mechanical damage. When foliage was damaged, injured cabbage and canola plants were preferred for oviposition over intact conspecifics, whereas injured Chinese cabbage plants were less preferred than intact conspecifics. However, when root tissue was damaged, intact cabbage and canola plants were preferred over injured conspecifics, whereas moths did not discriminate between root‐damaged and intact Chinese cabbage plants. Injury to upper leaves significantly affected the intra‐plant distribution of eggs. In cabbage and canola plants, injury to leaf 6 significantly increased the number of eggs laid on this leaf, resulting in a significant decrease in the number of eggs laid on the lower foliage/stem of plants, whereas in Chinese cabbage plants it significantly decreased the number of eggs laid on leaf 6. Following oviposition on intact plants, neonate larvae established the vast majority of feeding sites on leaves 5–8 in all three host plants, indicating that larvae moved a considerable distance from preferred oviposition sites in cabbage and canola plants. The growth rate of neonates fed on leaf‐6 tissue was significantly greater than that of those fed on leaf‐1 tissue; >90% of larvae completed development when fed exclusively on leaf‐6 tissue but no larvae completed development when fed exclusively on leaf‐1 tissue. The study demonstrates the complex and unpredictable interactions between P. xylostella and its host plants and provides a basis from which we can begin to understand observed distributions of the pest in Brassica crops.     

Transmission of Iris yellow spot virus by Frankliniella fusca and Thrips tabaci (Thysanoptera: Thripidae)

Thrips-transmitted Iris yellow spot virus (IYSV) (Family Bunyaviridae, Genus Tospovirus) affects onion production in the United States and worldwide. The presence of IYSV in Georgia was confirmed in 2003. Two important thrips species that transmit tospoviruses, the onion thrips (Thrips tabaci (Lindeman)) and the tobacco thrips (Frankliniella fusca (Hinds)) are known to infest onion in Georgia. However, T. tabaci is the only confirmed vector of IYSV. Experiments were conducted to test the vector status of F. fusca in comparison with T. tabaci. F. fusca and T. tabaci larvae and adults reared on IYSV-infected hosts were tested with antiserum specific to the nonstructural protein of IYSV through an antigen coated plate ELISA. The detection rates for F. fusca larvae and adults were 4.5 and 5.1%, respectively, and for T. tabaci larvae and adults they were 20.0 and 24.0%, respectively, indicating that both F. fusca and T. tabaci can transmit IYSV. Further, transmission efficiencies of F. fusca and T. tabaci were evaluated by using an indicator host, lisianthus (Eustoma russellianum (Salisbury)). Both F. fusca and T. tabaci transmitted IYSV at 18.3 and 76.6%, respectively. Results confirmed that F. fusca also can transmit IYSV but at a lower efficiency than T. tabaci. To attest if low vector competency of our laboratory-reared F. fusca population affected its IYSV transmission capability, a Tomato spotted wilt virus (Family Bunyaviridae, Genus Tospovirus) transmission experiment was conducted. F. fusca transmitted Tomato spotted wilt virus at a competent rate (90%) suggesting that the transmission efficiency of a competent thrips vector can widely vary between two closely related viruses.     

Flower visitation and oviposition behavior of Frankliniella occidentalis (Tysan., Thripidae) on cucumber plants

Oviposition behaviour of western flower thrips, Frankliniella occidentalis (Pergande) on greenhouse cucumber, Cucumis satifus (L.) was investigated. Most eggs were laid in the leaves, along veins and under leaf hairs, with only a few on plant stems and flowers. Oviposition rate was higher during the day than during the night. During the day, more adult thrips were found in the flowers than during the night. The number of adult thrips per flower increased rapidly after sunrise with the highest densities occurring around noon and thereafter the number of thrips in flowers decreased during the afternoon. No differences were found in the number of larvae (first and second instars) in flowers during the same period. The number of adult thrips on male and female cucumber flowers was not different, indicating that pollen is not the only attraction in flowers for thrips.     

Fecundity and egg distribution of the herbivore Spodoptera pectinicornis as influenced by quality of the floating aquatic plant Pistia stratiotes

We determined the influence of larval host quality of the floating aquatic weed Pistia stratiotes L. (Araceae) on the fecundity and egg distribution of the biological control agent Spodoptera pectinicornis (Hampson) (Lepidoptera: Noctuidae). Different nutritional levels were produced by growing plants with relatively low and high levels of nitrogen, phosphorus and potassium fertilizer. Female and male pupal biomass were significantly greater when the larvae were fed leaves from the high fertilizer plants. Although the fertilizer treatments did not significantly influence total fecundity, there was an indirect effect as adults from larger pupae were more fecund. Regardless of treatment, ovipositing females formed a depression in the leaf surface by removing trichomes into which they deposited the egg masses. Most of the egg masses were laid on the lower leaf surface, on leaf positions 5–8 (counting from the young inner to the outer leaves) and during days 1–2 post-eclosion. Most of the eggs were laid in masses but about 12% were solitary. Females fed the low fertilizer treatment laid a greater proportion (mean ± s.e.) of their eggs as solitary eggs (17.3 ± 3.4% of total eggs) than did females fed the high fertilizer treatment (8.3 ± 2.3% of total eggs). The increased percentage of solitary eggs laid by the females from the low quality larval diet may be an adaptive response to decrease competition among the progeny.     

Effects of undersown clover on host-plant selection by Thrips tabaci adults in leek

The suppressive effects of undersown clover on Thrips tabaci Lindeman infestation in leek is known but not the stages in thrips population dynamics that are affected by intercropping and the mechanisms involved. Colonization or settling of adult onion thrips (T. tabaci) in monocropped leek (Allium porrum L.) and in leek intercropped with strawberry clover (Trifolium fragiferum L.) was studied in two potted plant experiments. Potted leek plants with and without undersown clover were placed for a short period (2 and 5 days) in monocropped or intercropped field plots when high thrips infestation was expected. Thrips adults were counted on all leaves and in the shaft during this observation period. Thrips populations were monitored weekly in the field plots throughout the entire growing season.In both potted plant experiments, there were consistently fewer thrips adults on intercropped leek plants than on monocropped plants. The plant growth parameters – number of leaves and stem diameter – were similar in all treatments and thus did not explain differences in thrips adults. Natural enemies were absent on both leek and clover, and thus cannot explain the differences in adult thrips numbers. Furthermore, no adults of T. tabaci were found on the clover in the potted plant experiment and only very few in the field experiment. Thus it was concluded that strawberry clover was not an effective trap crop for thrips.In the second potted plant experiment, clover was removed just before the leek plants were introduced to the field, thus eliminating direct physical, visual and olfactory interference by clover. After the undersown clover was removed, the leek plants harboured only one-third of the number of thrips adults, as compared to the monocropped plants. This study supports the notion that there are subtle links between intercropping and plant quality, and indicates that host-plant quality is an underlying cause of the reduction in adult thrips numbers in leek/clover intercropping.     

喷施吲哚-3-乙酸 (IAA) 对番茄及其上B型烟粉虱的影响

【目的】不同植物生长调节物质对植食性昆虫产卵、发育、取食等常有促进或抑制作用,进而影响植物与昆虫的互作关系。本研究旨在阐明常用的植物生长调节剂吲哚-3-乙酸对B型烟粉虱Bemisia tabaci (Gennadius)的影响,进而探索防治烟粉虱环境友好的方法,同时期望获得更加优质的烟粉虱用作替代寄主饲养寄生蜂。【方法】对番茄 Solanum lycopersicum L.植株外源喷施吲哚-3-乙酸(IAA),检测其生理生化的响应;记录B型烟粉虱存活率、产卵量并测量解毒酶等指标。【结果】喷施IAA后番茄叶片含水量略有上升,叶面积增大,叶绿素含量增加,过氧化物酶(POD)活性降低,多酚氧化酶(PPO)活性升高,超氧化物歧化酶(SOD)活性变化不显著(P＞0.05)。喷施IAA后番茄上B型烟粉虱成虫存活率高于对照组,其中50 mg/L IAA番茄上B型烟粉虱成虫存活率和总产卵量最高,250 mg/L IAA存活率最低;喷施IAA 120 h后烟粉虱总产卵量升高;碱性磷酸酶(AKP)、超氧化物歧化酶(SOD)活性较对照升高。【结论】喷施不同浓度的IAA溶液后,番茄植株的生理生化水平发生不同程度的改变,烟粉虱成虫的存活状况、产卵量以及体内解毒活性也会产生不同程度的改变。适宜剂量的IAA处理能够使烟粉虱的生存表现更加优异,从而为饲养寄生蜂提供优质的替代寄主。     

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator? 2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips. 3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside. 4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.     

日本刀角瓢虫对不同番茄品种的产卵选择性及其影响因素

【目的】明确日本刀角瓢虫Serangium japonicum对叶毛密度和类型不同的番茄Lycopersiconesculentum品种的产卵选择性。【方法】以4个番茄品种(砧木101、闽粉樱1号、砧木301和以色列超级金刚)作为日本刀角瓢虫的寄主植物,观察番茄叶片背面超微结构,统计叶片背面叶毛类型及密度;用叶蝶法和植株法测定日本刀角瓢虫雌成虫在带烟粉虱Bemisia tabaci卵的4个番茄品种上的产卵量占比;并测定日本刀角瓢虫在这4个番茄品种叶片上的子代及成虫表现(生长发育、繁殖和捕食能力)以及对叶片的附着力,雌成虫对4个番茄品种健康叶片和受烟粉虱为害叶片的气味选择以及4个番茄品种叶碟和植株上日本刀角瓢虫卵被同类捕食的风险。【结果】4个番茄品种叶片背面叶毛类型均具有非腺毛和腺毛,其中,非腺毛有Ⅱ, Ⅲ和Ⅴ型,腺毛有Ⅰ, Ⅳ Ⅵ和Ⅶ型,且均以Ⅴ型非腺毛密度最高。以色列超级金刚叶片背面的叶毛密度显著低于其他3个供试番茄品种。日本刀角瓢虫偏好在以色列超级金刚上产卵,在以色列超级金刚、砧木101和闽粉樱1号上的繁殖力(165~223.92粒/雌)显著高于在砧木301上的(2809粒/雌)。日本刀角瓢虫子代由卵发育至成虫的历期在闽粉樱1号上最短(15.73 d),在砧木101上最长(23.00 d)。日本刀角瓢虫在4个番茄品种上的产卵选择性与子代表现及亲代表现无显著相关性,而与日本刀角瓢虫卵的被捕食风险存在显著正相关关系。日本刀角瓢虫在4个番茄品种上的产卵选择性与日本刀角瓢虫对番茄叶片的附着力及番茄叶片上各类型叶毛密度均无显著相关性。番茄的7种叶毛类型其叶毛密度在4个番茄品种上都存在显著差异,除番茄Ⅰ型腺毛密度与日本刀角瓢虫的繁殖力(30 d内单雌产卵量)存在显著负相关关系外,其他6种类型的叶毛密度与日本刀角瓢虫子代表现及亲代表现均无显著相关性。日本刀角瓢虫雌成虫对4个番茄品种的气味无明显偏好。日本刀角瓢虫卵在4个番茄品种叶蝶和植株上的被捕食比例差异显著。【结论】日本刀角瓢虫雌成虫偏好在叶毛密度低的番茄品种叶片上产卵,番茄腺毛对日本刀角瓢虫成虫生命活动影响显著。     

Overwintering locations and hosts for onion thrips (Thysanoptera: Thripidae) in the onion cropping ecosystem in New York

Identifying locations where onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), overwinter and subsequently disperse is important for designing control strategies. In upstate New York from 2003 through 2006, potential overwintering sites in the commercial onion, Allium cepa L., cropping system were investigated early in the spring before onion seedling emergence and again late in the season after onions were harvested. Onion thrips adults were sampled directly from the soil and indirectly from the soil by using emergence cages. Sampling locations included onion field interiors and edges and areas outside of these fields, including woods. Host material sampled included onion culls; volunteer onions, which sprout from cull onions left behind after harvest; and weeds. Onion thrips adults were found in all sections of onion fields and in locations outside of onion fields, with the fewest emerging from woods. Emergence began in early May and extended into June. Peak emergence occurred during the last half of May, at which time 50-75% of the population had emerged. Adults colonized volunteer onions as early as late March and as late as mid-November. No adults were found overwintering in onion cull piles. Adults also colonized several weed species, especially pigweed, Amaranthus hybridis L., and lambsquarters, Chenopodium album L., late in the fall. Our results indicate that onion thrips adults overwinter in the soil within and near onion fields and that they probably colonize volunteer onion plants before subsequent generations infest the onion crop in the spring. Volunteer onions and weeds also provide onion thrips with a host after onions are harvested. Consequently, onion thrips management strategies should include tactics that reduce volunteer onion and weed abundance.     

Relationship between onion thrips (Thrips tabaci) and Stemphylium vesicarium in the development of Stemphylium leaf blight in onion

Stemphylium leaf blight caused by Stemphylium vesicarium and onion thrips (Thrips tabaci) are two common causes of leaf damage in onion production. Onion thrips is known to interact synergistically with pathogens to exacerbate plant disease. However, the potential relationship between onion thrips and Stemphylium leaf blight is unknown. In a series of controlled laboratory and field trials, the relationship between thrips feeding and movement on the development and severity of Stemphylium leaf blight were examined. In laboratory assays, onions (“Avalon” and “Ailsa Craig”) with varying levels of thrips feeding damage were inoculated with S. vesicarium. Pathogen colonisation and leaf dieback were measured after 2 weeks. In pathogen transfer assays, thrips were exposed to S. vesicarium conidia, transferred to onion and leaf disease development was monitored. In field trials, insecticide use was examined as a potential indirect means to reduce Stemphylium leaf blight disease and pathogen colonisation by reducing thrips damage. Results from laboratory trials revealed that a reduction in thrips feeding decreased S. vesicarium colonisation of onion leaves by 2.3–2.9 times, and decreased leaf dieback by 40–50%. Additionally, onion thrips were capable of transferring S. vesicarium conidia to onion plants (albeit at a low frequency of 2–14% of plants inoculated). In field trials, the symptoms and colonisation of Stemphylium leaf blight were reduced by 27 and 17%, respectively with the use of insecticide to control thrips. These results suggest that onion thrips may play a significant role in the development of Stemphylium leaf blight, and thrips control may reduce disease in commercial onion fields.     

Evaluation of sampling methodology for determining the population dynamics of onion thrips (Thysanoptera: Thripidae) in Ontario onion fields

Onion thrips, Thrips tabaci Lindeman, are an economic pest of alliums worldwide. In Ontario onion-growing regions, seasonal abundance and population trends of onion thrips are not well known. The objectives of this research were to investigate onion thrips population dynamics by using both white sticky traps and plant counts, to gain insight into flight height, and to determine the genus and sex of thrips fauna present in monitored fields. Adult thrips were captured on white sticky traps placed in two commercial onion fields in the Thedford-Grand Bend Marsh region as early as mid-May in 2001, 2002, and 2003. Thrips were not recorded on onion plants in these fields until late June and early July. A comparison of sticky trap captures to plant counts revealed a strong, positive correlation, indicating that sticky traps, which consistently detected thrips earlier than plant counts, could be used instead of plant counts early in the season to monitor onion thrips populations. Pole traps placed in onion and an adjacent soybean, Glycine max (L.) Merr., field revealed that regardless of crop type, most thrips were captured 0.7-0.95 m above the soil surface. During this study, 70% of 137,000 thrips captured on sticky traps and 89% of 1,482 thrips captured in pan traps were female onion thrips. No male onion thrips were identified in this study: most of the remaining thrips were Frankliniella spp.     

日本刀角瓢虫对不同叶毛密度茄子品种的产卵选择性

【目的】产卵是昆虫发育过程中繁衍后代、维持种群数量的重要环节。在前期研究发现日本刀角瓢虫Serangium japonicum喜欢在茄子Solanum melongena叶片上产卵的前提下,本研究旨在深入探究日本刀角瓢虫对不同叶毛密度茄子品种的产卵选择性,以期进一步明确植物叶毛介导的日本刀角瓢虫产卵选择机制。【方法】观察日本刀角瓢虫雌成虫在4个茄子品种(黑到底、黑妞、日友长直壮、络星)叶碟和植株上的产卵选择性,测定不同茄子品种上日本刀角瓢虫后代的生长发育及成虫的繁殖力、捕食能力和对叶片的附着力,观察4个茄子品种叶片背面超微结构,测定日本刀角瓢虫雌成虫对茄子叶片的气味选择,测量茄子叶片上烟粉虱Bemisia tabaci卵粒的长度和宽度,测定日本刀角瓢虫卵被其雌成虫的同类捕食风险。【结果】日本刀角瓢虫偏好在黑到底上产卵,后代个体在黑到底品种上总发育历期(15.41±0.21 d)最短,亲代单雌产卵量(877.44±15.27粒/头)最高。但是,日本刀角瓢虫的产卵量占比与子代生长表现(发育历期、存活率和成虫体重)和成虫生存表现(繁殖力和捕食能力)均无显著相关性,而与叶片背面叶毛密度和长度存在显著正相关性;日本刀角瓢虫在茄子叶碟上的产卵量占比与日本刀角瓢虫雌成虫附着力存在显著正相关性。日本刀角瓢虫雌成虫附着力与叶毛密度显著正相关,而与亲代生长表现无显著相关关系。茄子叶片气味、猎物质量以及被同类捕食风险均不显著影响日本刀角瓢虫的产卵选择。【结论】茄子叶片背面叶毛密度及叶毛介导的日本刀角瓢虫附着力在日本刀角瓢虫对茄子叶片的产卵选择性中起重要作用。     

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.     

Diamondback moth egg susceptibility to rainfall: effects of host plant and oviposition behavior

Oviposition patterns of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), differ between common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae) host plants. This study shows that the moth prefers to oviposit on adaxial rather than abaxial leaf surfaces and petioles of both host plants. More eggs were laid in leaf veins than on leaf laminas of both host plants, especially in Chinese cabbage, where 94.6% of eggs were laid in veins. On Chinese cabbage, very few eggs were laid in clusters (≥2 eggs), whereas on common cabbage approximately 30% of eggs were laid in groups of 2 or more eggs. Removal of wax from common cabbage leaves dramatically increased the number of eggs laid singly on the leaf lamina of treated plants, suggesting that leaf waxes affect how eggs are distributed by ovipositing DBM. Eggs were most susceptible to removal by rainfall from the plant surface immediately (<1 h) after oviposition and when close to hatching (>72h old) whereas they were least susceptible 24 h after oviposition. Eggs laid on common cabbage plants were more susceptible to simulated rainfall than eggs laid on Chinese cabbage plants. On common cabbage plants, egg susceptibility to rainfall on different plant parts ranked adaxial leaf surfaces>petioles = abaxial leaf surfaces>stem, but there was no difference in egg susceptibility to rainfall on the various plant parts of Chinese cabbage. Furthermore, on common cabbage plants, eggs laid on both adaxial and abaxial leaf surfaces were afforded significant protection from the effects of rainfall by leaves higher in the plant canopy. On common cabbage plants, oviposition patterns reduce the potential impact of rainfall on eggs, possibly reducing the effect of this important abiotic mortality factor in the field.     

ToCV单独侵染和TYLCV&ToCV复合侵染番茄植株上烟粉虱寄主适应性及寄主植物营养成分含量和防御反应变化

[目的]本研究以番茄褪绿病毒(tomato chlorosis virus,ToCV)和番茄黄化曲叶病毒(tomato yellow leaf curl virus,TYLCV)为主体,旨在明确ToCV单独侵染及TYLCV&ToCV复合侵染对烟粉虱Bemisia tabaci MED隐种寄主适应性的影响,并从寄主植物营...     

Within-plant distribution of Bemisia tabaci (Homoptera: Aleyrodidae) adults and immatures on greenhouse-grown winter cucumber plants

Within-plant distribution of adults, pupae, nymphs, and eggs of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on leaves of greenhouse-grown winter cucumber, Cucumis sativum L., plants were studied in field plots for integrated pest management decision making. Distribution of specific life stages depended on the leaf positions. The leaves with most abundance and low or lowest variation of whiteflies were leaves 8-12 for adults, 8-11 for pupae, 6-12 for nymphs, and 6-9 for eggs. In light of the criterion in selecting within-plant sample sites with pest abundance and low variation, these leaves were considered as the most convenient for sampling specific life stages of B. tabaci. Single a and b values for each life stage of the whitefly were calculated by Taylor's power law and were used to estimate minimum sample sizes at a precision of 0.25 (SE/mean). The minimum sample size decreased with increasing density of adults on leaves 8-12, of nymphs on leaves 7 and 8, and of eggs on leaf 6, but slightly increased with increasing density of pupae on leaves 8-11, of nymphs on leaves 6 and 9-12, and of eggs on leaves 7-9.