How much pollen can thrips destroy?

ABSTRACT. 1. A laboratory technique for measuring the number of pollen grains consumed by thrips is described.
2. Thrips imaginis Bagnall and Thrips obscuratus (Crawford) (Thripidae) were studied particularly on pollen of the kiwifruit Actinidia deliciosa (A. Chevalier) Liang & Ferguson in New Zealand, and Echium plantagineum L. in Australia.
3. Mean daily feeding rates (in grains per thrips per day) ranged from 29 to 843, with an individual rate as high as 1626 for T.imaginis larvae II on E. plantagineum.
4. The time taken to feed on a single grain was proportional to grain volume, and decreased with temperature.
5. Daily feeding rates were significantly different between pollens, and were higher for smaller grains. The total volume of pollen contents consumed and the total time spent ingesting this volume per thrips per day may be constant with respect to pollen species.
6. Daily feeding rates were equivalent to 0.2–0.7% of the average total pollen production of a flower per thrips per day.
7. Extrapolation of the daily feeding rates suggests that pollen damage by thrips could sometimes be reducing crop yield or plant fitness.     

Aggregation and mating of thrips in flowers of Calystegia sepium

Abstract. 1. Aggregation and mating of Thrips major Uzel and Thrips fuscipennis Haliday (Thysanoptera: Thripidae) in the 1-day flowers of Calystegia sepium (L.) R.Br. are described.
2. The number of thrips per flower increased rapidly after flower-opening at dawn and decreased during the evening and following morning.
3. Males patrolled the corolla, attempting to copulate with any females that landed. Their movement was affected by the density of thrips on the corolla. Most females were among the stamens and style, apparently feeding on pollen.
4. These thrips were also abundant in flowers of Filipendula ulmaria (L.) Maxim. They fed on pollen, and grains adhered to them. They may be significant pollinators because of their high frequency of flights.
5. The aggregations appear to be a simple consequence of general flower-finding responses to colour and scent that are particularly elicited by flowers of C.sepium and F.ulmaria. The ecological significance of male aggregations is discussed.     

The coincidence of thrips and dispersed pollen in PNRSV-infected stonefruit orchards – a precondition for thrips-mediated transmission via infected pollen

Recent laboratory studies have demonstrated that Prunus necrotic ringspot virus (PNRSV) (family Bromoviridae) can be readily transmitted when thrips and virus‐bearing pollen are placed together on to test plants. For this transmission mechanism to result in stonefruit tree infection in the field, PNRSVbearing pollen must be deposited onto surfaces of stonefruit trees on which thrips also occur. In a previous paper, we demonstrated that almost all pollen in a PNRSV‐infected Japanese plum orchard in southeastern Queensland was deposited onto flowers, whereas few grains occurred on leaves and none on stems. Here, we present results of our investigation of thrips species composition, distribution and abundance on stonefruit trees in the same study area as our previous pollen deposition study. We collected a total of 2010 adult thrips from 13 orchards during the 1989, 1991 and 1992 flowering seasons of which all but 14 were in the suborder Terebrantia. Most (97.4%) terebrantian thrips were of three species, Thrips imaginis, Thrips australis and Thrips tabaci. Thrips tabaci as well as species mixtures that included T. imaginis, T. australis and T. tabaci have been shown to transmit PNRSV via infected pollen in laboratory tests. Adult thrips were frequently collected from flowers but rarely from leaves and never from stems. Large and significant differences in numbers of T. imaginis, T. australis and T. tabaci adults in flowers occurred among orchards and between seasons. No factor was conclusively related to thrips numbers but flowers of late‐flowering stonefruit varieties tended to hold more thrips than those of early‐flowering varieties. Our results indicate that the common thrips species present on stonefruit trees in the Granite Belt are also ones previously shown to transmit PNRSV via infected pollen in the laboratory and that these thrips are concentrated in tonefruit flowers where most stonefruit pollen is deposited. These results contribute to mounting circumstantial evidence that stonefruit flowers may be inoculated with PNRSV via an interaction of thrips with virus‐bearing pollen and that this transmission mechanism may be an important cause of new tree infections in the field     

The Potential for Pollen-borne Virus Transfer in a Plum Orchard Infected With Prunus Necrotic Ringspot Virus

Prunus necrotic ringspot virus (PNRSV) is borne in stonefruit pollen. Previous work has shown that virus particles can enter cucumber seedlings when virus-bearing pollen grains contact puncture holes made in plant cells by thrips feeding. Stonefruit plant parts on which pollen is deposited and thrips spend considerable time feeding, are likely sites of PNRSV inoculation. The principal agents of pollen deposition may therefore play a key role in PNRSV epidemiology. We determined the principal sites of pollen deposition on Japanese plum trees and the major pollen depositing agents in a PNRSV-infected orchard in southeastern Queensland. Plum pollen was deposited mostly onto flowers, with few grains being found on leaves or stems. Within the flowers, pollen grains were distributed mostly on the petals, but some were found on the sepals, filaments and carpels. Honey bees were the most frequent visitors to plum flowers and they deposited more than any other insects. Flies visited flowers at low frequencies and also deposited pollen. Significant amounts of pollen were deposited onto flowers by unidentified nocturnal agents. Thrips were not observed during the study period, although they were present in the orchard. Previous studies have assumed that thrips carry virus-bearing pollen as well as bring it into proximity of feeding wounds. Our results suggest that, although thrips carriage of pollen may occur, it is not necessary for PNRSV spread in stonefruit orchards.     

Pollen-feeding and the host specificity and fecundity of flower thrips (Thysanoptera)

Abstract. 1. Flower thrips could feed on pollen of a wide range of sizes and were unaffected by exine spines. One species of thrips was unable to feed on very adhesive grains.
2. The proportion of time spent feeding on each species of pollen (in seconds per minute of exposure) reflected the known host specificities. Host-specific thrips could distinguish their host pollen, apparently without probing.
3. Kakothrips pisivorus (Westwood) appeared to have a higher rate of ingestion of a host pollen than of four non-host pollens.
4. In cages in the laboratory, Thrips fuscipennis Haliday laid significantly more eggs over 48h when given pollen than when given other floral tissues or no food. K. pisivonis and Ceratothrips ericae (Haliday) also laid significantly more eggs over 48h in the presence of pollen than in its absence.
5. In comparisons between pollen diets, T. fuscipennis, a generalist, laid similar numbers of eggs with each species of pollen, but K. pisivorus and C. ericae laid significantly more eggs with their respective host pollens. The differences in oviposition rate between pollen diets reflected the differences in the proportion of time spent feeding.     

Ecological studies on Thrips imaginis Bagnall (Thysanoptera) in flowers of Echium plantagineum L. in Australia

Aspects of the ecology of Thrips imaginis Bagnall in flowers of Echium plantagineum L. are described and subjected to experimental analysis. Thrips eggs were mostly laid in plant parts that were not lost when the short-lived flowers abscissed. The abundance of adults and larvae in flowers from the bud stage through to abscission was determined. Larvae usually required more than one flower to complete development and so had to migrate between flowers to survive. Larvae generally remained between the bases of the stamen filaments when in direct sunlight, but moved along the filaments to the anthers for rapid pollen feeding during low light intensity, especially at night. There was little spatial and temporal overlap between thrips larvae and honeybees in the flowers. Ants can cause much damage to the flowers and can feed on thrips. Pollen feeding of T. imaginis is described. The species of pollen grain affects feeding, and this may influence breeding success. Low u.v.-reflecting white, blue and yellow water traps caught more T. imaginis that green, red, black and high u.v.-reflecting white. These results agree well with the numbers of adults in several native and non-native flowers of various colours. Adult female thrips colour variation is correlated with for ewing length, and hence reflects factors acting on a pre-adult stage.     

Evaluation of an improved method for mass-rearing of thrips and a thrips parasitoid

Improved laboratory methods are described in detail for mass rearing of various thrips species, such as Frankliniella occidentalis, Frankliniella intonsa, Thrips palmi, Thrips tabaci (Thysanoptera: Thripidae) and a thrips parasitoid, Ceranisus menes (Hymenoptera: Eulophidae), using various foods. In one method, plant pollen and honey solution are used as food sources. In a second method, germinated broad bean seeds are used. Eggs, produced in large numbers in water, are collected by a suction funnel onto a filter paper and incubated in a Petri dish. Large numbers of larvae that hatch are collected by using food traps (plant pollen). Larvae can be reared on pollen or on germinated broad bean seeds until adult emergence without additional water and food. This method has been found useful for producing even-aged thrips at different densities (up to 500 larvae in a cage of 80 mm diameter) with relatively low mortality rates. Evaluation of this rearing method for F. intonsa, shows that during 2 weeks at 20 °C per 100 females more than 4000 females could be produced in the next generation. About 5 min per day is required to achieve this productivity of mass production. The method is also suitable for producing large numbers of the solitary endoparasitoid of thrips larvae, C. menes.     

Predatory mites avoid ovipositing near counterattacking prey

Attacking prey is not without risk; predators may endure counterattackby the prey. Here, we study the oviposition behaviour of a predatory mite(Iphiseius degenerans) in relation to its prey, thewesternflower thrips (Frankliniella occidentalis). This thrips iscapable of killing the eggs of the predator. Thrips and predatory mites - apartfrom feeding on each other - can also feed and reproduce on a diet of pollen.Because thrips may aggregate at pollen patches, such patches may be risky foroviposition by the predatory mites. We found that, in absence of thrips,predatory mites lay their eggs close to pollen, but further away when thripsarepresent. Predatory mite eggs near pollen were killed more frequently by thripsthan when they were deposited further away. The oviposition behaviour of thepredatory mite was also studied in absence of thrips, but in presence of thealarm pheromone of thrips. This pheromone is normally secreted upon contactwithpredators or competitors. When applied close to the pollen, predatory mitesoviposited significantly further away from it. When the alarm pheromone wasapplied away from the food source, most eggs were found near the pollen. Theseresults indicate that female predatory mites show flexible ovipositionbehaviourin response to the presence of their counterattacking prey.     

Comparing Behavioural Patterns of Thrips tabaci Lindeman on Leek and Cucumber

This study documents the behavioural repertoire of Thrips tabaci. Seventeen behavioural elements shown by adult females were videotaped, described and classified into seven behavioural categories. The comparison of thrips behaviour on leek and cucumber over 24 h (L:D = 16:8) revealed that on cucumber thrips spent significantly less time being inactive, but significantly more time with feeding resulting in significantly higher feeding damage compared to leek. Oviposition behaviour incidence and oviposition rate were somewhat, but not significantly lower on cucumber compared to leek. Sequences of leaf surface exploration lasted significantly longer on cucumber than on leek. Thrips females were as active during light as during dark periods. Our results show that T. tabaci females spend different amounts of time with resting, feeding and explorative behaviours on leek and cucumber, thus indicating differences in host use on these two crops.     

Transmission of prunus necrotic ringspot virus using plum pollen and thrips

Prunus necrotic ringspot virus (PNRSV) was transmitted to cucumber but not to peach seedlings after they were dusted with infective plum pollen and caged with 8–10 thrips per seedling for 24 h. When the pollen was taken from three plum trees shown by mechanical inoculation tests to have highly infective flower buds and pollen, the transmission rates to cucumber seedlings were 56% with Thrips tabaci and 66% with a mixture of five thrips species collected from Ageratum houstonianum flowers. However, the transmission rate averaged only 7% when pollen was taken from five other plum trees which had flowers with less infectivity in sap transmission tests. In 1990 T. imaginis, T. tabaci and T. australis, which were present in the mixture of thrips from A. houstonianum, also formed the major part of the thrips population in flowers of the plum trees used as the pollen source.     

HETEROSTYLY,POPULATION COMPOSITION,AND POLLEN FLOW IN HEDYOTIS CAERULEA

Hedyotis caerulea is a perennial, spring-flowering herb native to eastern North America with distylous flowers that differ in a number of morphological and physiological traits. However, the pin and thrum morphs produce the same numbers of buds, flowers, and fruits per plant, although it is possible that differences in these may occur in some populations at certain times of the flowering period. The two morphs are self-incompatible and cross-compatible. Most populations contained an excess of pins over thrums (anisoplethy); less commonly pins and thrums were equally represented (isoplethy). Populations change from anisoplethy to isoplethy and in the reverse direction. The spatial distribution of pin and thrum flowers in populations was random in some populations but non-random in others. There is some indication that the two morphs in some populations have somewhat different flowering periods. Pollinators seem to be chiefly bombyliid flies and perhaps thrips, but insects were rarely observed visiting flowers. In some populations, the two morphs produced equal numbers of pollen grains per flower; in others they did not. The average pollen viability varied, but on the average there was a moderate level of pollen sterility. High numbers of pollen grains remained in dehisced anthers, probably as a result of low pollinator activity. However, between 5% and 9% of the pollen produced participated in pollination. Stigmas of most pin flowers received more pin pollen grains than thrum pollen grains; on stigmas of thrum flowers pin pollen grains outnumbered thrum pollen grains. Thus, compatible pollen flow from pins to thrums was greater than in the reverse direction. Anisoplethic and isoplethic populations had the same pollen flow patterns. A plant-by-plant examination of stigmas indicated that many stigmas bore few or no pollen grains. Seed production of the two morphs was equal. Despite the inequities in pollen flow patterns, the widespread and occasionally weedy nature of H. caerulea suggests that its breeding system must be viewed as a successful one.     

Genetic variation in chrysanthemum for resistance toFrankliniella occidentalis

In a choice-experiment, 42 chrysanthemum cultivars were screened for resistance toFrankliniella occidentalis (Pergande). Oviposition preference, two types of feeding damage and thrips numbers per flower were recorded as measures of resistance. A large genetic variation in thrips resistance was found among the cultivars screened. The amount of feeding damage was strongly determined by oviposition preference. Besides, a positive correlation was found between the oviposition preference in non-flowering chrysanthemums (number of eggs) and flowering chrysanthemums (number of thrips per flower). Thrips feeding on young, developing tissues, causes growth damage because affected cells are unable to expand and leaves become distorted. Thrips feeding on older, expanded leaves causes cells to become filled with air, resulting in ‘silver’ damage. The amounts of growth-and ‘silver’ damage were negatively correlated suggesting that thrips chose either young or older leaves to feed on. The order of resistance among cultivars did not change during the experiment. In order to get more insight in resistance mechanisms the influence of some plant- and flower characters on resistance was examined. The plant characters height, number of leaves, flower production and flower weight were all negatively correlated with resistance. It is suggested that tall chrysanthemum cultivars with many and large flowers may invest less in defence than smaller cultivars, and therefore are more damaged by thrips.     

Analysis of the thrips fauna (Thysanoptera) on flowers of herbs

Studies of Thysanoptera were realized at the Agricultural Experimental Station in Mydlniki near Cracow over the years 2003-2005. This research work covers the observations of the species composition of thrips and the periods of the occurrence of the particulars species of thrips and their numerousness. The thrips were collected from flowers of Valeriana officinalis L., Hypericum perforatum L. and Levisticum officinale Koch. Following thrips species dominated samples collected directly from plants: Frankliniella intonsa (Trybom), Thrips fuscipennis Haliday, Thrips tabaci Lindeman and Thrips major Uzel. The greatest number of thrips was noticed during flowering period on Valeriana officinalis L., and Hypericum perforatum L.     

Effect of Watermelon Silver Mottle Virus on the Life History and Feeding Preference of Thrips palmi

Thrips-borne tospoviruses cause numerous plant diseases that produce severe economic losses worldwide. In the disease system, thrips not only damage plants through feeding but also transmit causative agents of epidemics. In addition, thrips are infected with tospoviruses in the course of virus transmission. Most studies on the effect of tospoviruses on vector thrips have focused on the Tomato spotted wilt virus–Frankliniella occidentalis system. Thus, we focused on another thrips-borne tospovirus, Watermelon silver mottle virus (WSMoV), to examine the effect of virus infection on its vector, Thrips palmi. In this study, the direct and indirect effects of WSMoV on the life history traits and feeding preference of T. palmi were examined. The survival rate and developmental time of the WSMoV-infected larval thrips did not differ significantly from those of the virus-free thrips. Comparing the developmental time of larval thrips fed on the healthy plants, thrips-damaged plants, and thrips-inoculated plants (the WSMoV-infected plants caused by thrips feeding), feeding on the thrips-damaged plants reduced the developmental time, and the WSMoV infection in host plants partially canceled the effect of thrips damage on the developmental time. In addition, no significant variations between the virus-free and WSMoV-infected adult thrips regarding longevity and fecundity were observed. These results implied that WSMoV did not directly affect the life history traits of T. palmi, but the WSMoV infection indirectly affected the development of T. palmi through the virus-infected plants. Furthermore, feeding preference tests indicated that T. palmi preferred feeding on either the thrips-damaged plants or the thrips-inoculated plants to the healthy plants. The effect of tospoviruses on the life history and feeding preference of vector thrips might vary among host plants, virus species, vector species, and environmental factors.     

The gum tree thrips Isoneurothrips australis Bagnall. Survival at different temperatures and humidities and its relation to capacity for dispersal

Thrips are carried long distances on the wind. Their ability to survive periods of fasting may determine their chance of completing such journeys alive. Thrips’survival was measured at various temperatures and humidities. Survival is best related to saturation deficit. This relation can be combined with meteorological data to calculate the survival time of thrips migrating at various times of year. From May to September inclusive a thrips can probably survive over 24 h in the air and runs little risk of death from desiccation. From December to March survival times average about 6h but can be as low as 3h on hot summer days.     

中国特有属牛筋条属的花粉形态与其系统位置

从发育的角度研究了中国特有单种属DichotomanthesKurz及与其系统学研究有关的外类群Prinsepiautilis的花粉形态 ,扫描电镜观察显示Dichotomanthes花粉粒自脱离四分体胼胝质膜开始至成熟二核花粉粒不同发育时期 ,花粉形态和外壁纹饰未见变化 ,仅花粉体积随成熟度增加而有所增大。而Prinsepiautilis ,其花粉粒刚脱离四分体时形状和成熟花粉明显不同 ,成熟花粉极面观为三裂圆形 ,赤道面观为圆形 ,外壁具清晰的平行条纹 ,但幼嫩花粉粒的形状很特别 ,极面观为深三裂圆形 ,赤道面观亦见花粉在两条沟之间下陷而沟部外突 ,明显为角萌发孔花粉 ,且花粉体积较成熟者小 ,而外壁纹饰同成熟者相比无根本性差异。前述两种植物花粉在不同成熟期体积有明显差异 ,而外壁纹饰在不同成熟期不存在质的变化并相对稳定 ,说明花粉外壁纹饰这一性状在蔷薇科中具有较为重要的分类学意义。DichotomanthesKurz具典型Rosaceae花粉的三孔沟结构 ,外壁具条纹 -穴状纹饰。将其孢粉学特征同Rosaceae 4个亚科有关类群的同类资料相比较 ,并结合其它形态解剖与细胞学等研究结果 ,支持将Dichotoman thes置入Maloideae下而不赞同将其另立亚科或置于Prunoideae之下。此外 ,由于Prinsepiautilis的花粉在其发育初期具角萌发孔花粉 ,与Cunoniacea     

Size-number trade-offs and pollen production by Papilionaceous legumes

The intra- and interspecific relations between the size and number of pollen grains were examined for 21 species of papilionaceous legumes to test for the trade-off expected from the subdivision of limited resources. We observed a tradeoff between pollen grain diameter and the number of grains produced per flower within 17 of the 21 species examined. For 12 of these species, the observed partial regression coefficient for In (pollen grain diameter) equaled -3, as expected. The remaining five species exhibited more negative partial regression coefficients than expected. Relations between pollen grain size and number that are more negative than expected may result from a decelerating relation between pollen grain size and the resource investment per grain. Flower production significantly influenced pollen production for only eight species so that pollen production seems to be determined primarily on a per flower basis. Interspecifically, pollen size also varied inversely with pollen number for the 21 species even after the effect of phylogenetic relatedness was removed. Pollen size varies relatively little compared to the number of pollen grains produced per flower and therefore may be the primary target of natural selection. The presence of a trade-off in pollen production probably constrains the evolutionary options by which flowering plants can maximize male success.     

Transmission of Three Strains of Tobacco Streak Ilarvirus by Different Thrips Species Using Virus-infected Pollen

When cucumber seedlings were dusted with tobacco streak ilarvirus (TSV)-infected pollen and infested with 5–10 thrips (adults and larvae mixed), Thrips tabaci transmitted all three Australian strains of TSV. In similar work, Microcephalothrips abdominalis transmitted both and Frankliniella schultzei one strain, respectively, of two TSV strains tested. Transmission of the Ageratum strain (TSV-Ag) infecting pollen of Ageratum houstonianum was very efficient (100%) by all three thrips species. However, transmission rates of only 0–28% were achieved using the Ajuga strain (TSV-A) and the strawberry strain (TSVS) in pollen of other hosts. A fourth thrips species, T. parvispinus , transmitted TSV-Ag from infected tomato pollen to Chenopodium amaranticolor seedlings. There was, therefore, little or no vector specificity in the thrips transmission of the three strains of TSV, but factors associated with the virus-infected pollen affected the efficiency of transmission. This is the first report of F. schultzei and T. parvispinus as vectors of TSV.     

Pollen interception by linyphiid spiders in a corn agroecosystem: implications for dietary diversification and risk-assessment

Dietary diversification, including consumption of plant tissues such as pollen, can enhance the fecundity of generalist predators, resulting in improved control of pest prey. Supplemental pollen feeding has been observed in many natural enemies, including sheet-web spiders (Araneae: Linyphiidae), which represent a major component of food webs in agroecosystems. Their horizontal, ground-based webs have the potential to intercept pollen grains during anthesis of crop plants, providing the opportunity for consumption of pollen to occur. In laboratory feeding trials, Frontinella communis and Tennesseellum formicum (Araneae: Linyphiidae) readily fed on pollen grains dusted on their webs, with 82 and 92% of spiders consuming pollen within the 210 min trial. These results revealed a strong potential for dietary supplementation with pollen in ground-based sheet-web spiders, indicating that pollen feeding may be an important component of the feeding biology of linyphiids. To measure pollen and prey interception in simulated linyphiid webs, a 20 m × 20 m grid of miniature sticky traps was established within and downwind of a corn agroecosystem. Traps were exposed for 24 h, all intercepted material was transferred to the laboratory for subsequent identification, and replaced with additional traps for 28 consecutive days in July and August 2008, to encompass periods before, during and after anthesis. Over 150,000 corn pollen grains and 5,000 prey items (dominated by Collembola and Hemiptera) were intercepted at simulated web-sites. Dates of peak anthesis resulted in pollen counts as high as 4,000 grains per web-site in the interior of the cornfield. Spatial Analysis by Distance Indices (SADIE) indicated significant temporal and spatial variability in pollen interception within and outside the corn field, but interestingly there was no significant spatial association between pollen and prey. Furthermore, transgenic Bacillus thuringiensis corn expresses insecticidal proteins in pollen, posing an exposure risk to non-target arthropods. Consumption of corn pollen may be a route to transgenic protein exposure in this important taxon of generalist predators.     

Pollen digestion by flower-feeding Scarabaeidae: protea beetles (Cetoniini) and monkey beetles (Hopliini)

Pollen protoplasm is very nutritious, but the hard and highly resistant outer wall (exine) of the pollen grain presents an obstacle that pollen-feeders must overcome to benefit from the valuable protoplasm. Pollen digestion in three pollen-eating scarab beetles, the green protea beetle Trichostetha fascicularis and two monkey beetle species, Peritrichia cinerea and Pachynema flavolineata, was investigated. Adult beetles were collected for observations of feeding mechanisms, scanning electron microscopy of mouthparts, and histological examination of gut contents. Serial sections of different regions along the gut were stained for different nutrients and examined to determine the appearance of the pollen grains and the removal of carbohydrates, proteins and lipids from the pollen. During feeding, beetles used dense brushes of setae on the tips of their maxillae to mop up nectar and sweep pollen into their mouths. Grains were ingested intact. Nutrients were effectively removed from the grains as they passed along the gut and most pollen grains in the hindgut were empty, with broken exines. All the beetles excreted the undigested exine. Comparison with other studies on pollen digestion by a variety of insect and vertebrate pollen-feeders suggests that digestive enzyme penetration of ingested pollen grains and exudation of the products of digestion is the most likely method used by these beetles.