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.     

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.     

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.     

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.     

Odour-baited traps influence thrips capture in proximal unbaited traps in the field

Two field experiments examined the distance over which an attractant odour of a volatile chemical could influence thrips capture in proximal traps that were without the odour. In each experiment a star‐shaped array of water traps consisted of a centre trap with or without an odour surrounded by odourless traps at 0.5, 1, 2, 5, and 10 m in eight equally spaced radial arms 45° apart. Experiments ran for 47 h (centre trap: ethyl nicotinate) or 7 h (centre trap: ethyl isonicotinate). Each had four replicates. With ethyl nicotinate, more thrips were trapped in the centre‐baited traps than in the unbaited centre traps (63×, 7×, 98× and 200× for total thrips, Thrips tabaci Lindeman ♀, and Thrips obscuratus Crawford ♀and ♂, respectively) (Thysanoptera: Thripidae). More total thrips and T. tabaci♀ were trapped in the centre traps baited with ethyl isonicotinate than in unbaited centre traps (21× for both). For ethyl nicotinate, numbers of T. obscuratus in unbaited traps downwind from the baited centre trap declined by 50% within 0.4 m (♀) and 2 m (♂) and by 95% within 3 m (both ♀ and ♂) based on model predictions. For ethyl isonicotinate, numbers of T. tabaci in unbaited traps downwind from the baited centre trap declined by 50% within 1.3 m and by 95% within 10 m based on model predictions. Wind direction was an important factor in the degree and direction of thrips capture with the highest thrips capture downwind from the centre trap with odour. There was no increase in numbers of T. tabaci in any traps without odour in the ethyl nicotinate‐centred array. Differences in trapping patterns between thrips species and odours indicated that there were thrips species–odour specific interactions. Experiments examining differences between traps with and without a thrips attractant odour need to be designed very carefully to ensure meaningful results especially in enclosed and/or low‐wind indoor situations.     

An immuno-marking technique for thrips

Rabbit immunoglobulin G (R‐IgG) was used successfully as an external mark for thrips. Females of both Thrips tabaci Lindeman and Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) were marked with 1 mg ml^?1 R‐IgG solution with 1%‘Tween 20’ by the contact exposure method. Determining the retention of the mark was by running the rinsing solution of individual thrips in an enzyme‐linked immunosorbent assay (ELISA). The sandwich ELISA method was used with an additional biotin–avidin step. The threshold for a positive marking score was defined as three times the mean optical density readings of the negative control thrips. Under laboratory conditions, on bean pods, all marked thrips scored positive up to 6 days after marking (DAM). When marked thrips were kept in the laboratory on marigold flowers for 2 days, they all scored positive. When marked and unmarked thrips were placed together on these flowers, the mark was transferred to 10–20% of the unmarked thrips and they became positive. Under field conditions, on sticky traps covered with water‐base glue, 100, 80, and 20% of the marked T. tabaci scored positive by the 3rd, 6th, and 9th DAM, respectively. Under the same conditions 100, 90, and 10% of the marked F. occidentalis scored positive by the 3rd, 6th, and 9th DAM, respectively. The retention of the R‐IgG decreased significantly under conditions of wetness and high humidity. After 6 days on chive plants kept at 80–100% r.h., all marked thrips scored negative while on plants kept at 40–60% r.h., 85% of the marked thrips scored positive. Rabbit IgG can be used as an external marker for thrips. The suitability of this marking method for dispersal studies of these important pests needs to be evaluated.     

Transmission of sowbane mosaic virus by Thrips tabaci in the presence and absence of virus-carrying pollen

When pollen of sowbane mosaic sobemovirus (SoMV)-infected Chenopodium amaranticolor was dusted onto C. amaranticolor and C. quinoa test seedlings which were then infested with 5–10 adult Thrips tabaci, SoMV was transmitted to 25%C. amaranticolor and 88% of C. quinoa plants. Five hours access of T. tabaci to pollen-contaminated C. quinoa seedlings was sufficient for SoMV transmission, but 1 h was not. SoMV was also transmitted when T. tabaci was mixed with pollen of C. amaranticolor and then placed on C. quinoa test seedlings. Further, plant-to-plant transmission of SoMV occurred in the absence of virus-carrying pollen when T. tabaci was caged on infected non-flowering C. amaranticolor or C. quinoa for 1–8 days and then adults transferred to C. quinoa test seedlings. This is the first time that thrips have been shown to be a vector of SoMV, and that a virus outside the ilarvirus group is reported to be transmitted using pollen and thrips.     

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.     

Determination of soil depth inhabited by Frankliniella occidentalis (Pergande) and Thrips tabaci Lindeman (Thysan., Thripidae) under greenhouse cultivation

The objectives of this study were to determine the depth of penetration into the soil by Frankliniella occidentalis (Pergande) and Thrips tabaci Lindeman (Thysan., Thripidae) in cucumber and tomato crops in greenhouses. A metal sampling apparatus sampled for the two species of thrips at five levels of soil depth (0–10 cm), over seven dates of sampling, each in eight replications. In general, thrips were found to be in greater numbers in the first 2 cm of soil, with the number of insects decreasing with depth increasing. In the depth of 8–10 cm, no insects were found. Number of thrips found in the soil under cucumber plants was greater in comparison with the tomato samplings. Frankliniella occidentalis was found in greater numbers in comparison with T. tabaci. The date of sampling showed a significant interaction with soil depth, with the number of insects found increasing from the first to the last date of sampling.     

Management of thrips (Thysanoptera: Thripidae) in Australian strawberry crops: within-plant distribution characteristics and action thresholds

Abstract  Management of thrips in a hydroponic strawberry crop near Sydney, New South Wales, was studied from 1999 to 2002. The main species present were western flower thrips, Frankliniella occidentalis (Pergande), plague thrips, Thrips imaginis Bagnall, and, occasionally, onion thrips, Thrips tabaci Lindeman. Their within- and between-plant distribution and the degree and type of damage caused are described, and used to recommend action thresholds. Flowers are identified as the primary monitoring site, and young green fruit as the key damage site. Action thresholds of approximately 45% of flowers with 5 or more adult western flower thrips, or 40% of flowers with 10 or more adult plague thrips are recommended. Alternative thresholds using all motile stages are given for flowers, and for young green and red berries. A higher tolerance is recommended during cool, wet periods.     

The Thrips orientalis group from South-east Asia and Australia: some species identities and relationships (Thysanoptera, Thripidae)

Abstract  A thrips associated in Thailand with the flowers of Paederia foetida , a rubiaceous weed in Florida that is a threat to Australia, is here recognised as Thrips morindae Priesner, a species previously considered a synonym of T. javanicus Priesner. Systematic relationships of these species with others in South-east Asia and the Australasian region are discussed. Two new species-groups are designated: the T. obscuratus group of six species from New Zealand and New Caledonia, and the T. orientalis group of 12 South-east Asian species that are associated with scented white flowers such as Gardenia . Four species of this second group are recorded from tropical Australia.     

An improved cage system for the bioassay of Metarhizium anisopliae on Thrips tabaci (Thysanoptera: Thripidae)

The ability of thrips and other minute insects to escape from conventional assay cups led to development of a successful assay chamber. In the present study, we evaluated three bioassay systems for thrips; Tashiro cage, microtube assay and leaf sandwich assay and introduced an improved thrips entomopathogenic bioassay system (TEBS). Our objective was to investigate the effect of Metarhizium anisopliae on Thrips tabaci using an easy-to-use and inexpensive holding chamber that would produce bioassay results with acceptable levels of accuracy and precision. In our assays, we found that escape of second-instar larvae from TEBS was significantly less than those of other methods which we tested. Our results indicated that our assay system was more suitable than the other conventional assays for the bioassay of entomopathogenic fungi on T. tabaci.     

Temporal and spatial dynamics of Tomato spotted wilt virus and its vector in a potato crop in Argentina

The nature of spatial and temporal dynamics of Tomato spotted wilt virus (TSWV) and its vector in a potato crop cv. Innovator without insecticide application is analysed. Seed tuber was analysed for the presence of TSWV as a source of initial inoculum. The presence of plants with symptoms of TSWV was evaluated by visual observation and DAS‐ELISA analysis to confirm the virus infection. Thrips species were collected from leaves and inflorescences and identified under stereomicroscope. The distribution of symptomatic plants and thrips species was recorded five times at 14 days intervals. The initial seed tuber infection was of 1.1%. Disease incidence was 0% at 29 days after planting (DAP), 0.2% at 43 DAP, 2.2% at 56 DAP, 11.6% at 70 DAP and 14.6% at 84 DAP. The progress of the disease was adequately described by a Logistic model [y = 0.15/(1 + 1205372.93 × exp (?0.22 × DAP))]. Thrips vector species identified as resident in the crop during the whole cycle were Thrips tabaci (n = 423), Frankliniella occidentalis (n = 141) and as occasional species, F. schultzei (n = 34) and F. gemina (n = 5) were found. At 43 and 56 DAP a random distribution pattern was observed and the thrips species found were T. tabaci (n = 188) and F. occidentalis (n = 105). An aggregated pattern was determined at 70 and 84 DAP. Spatial patterns of the disease spread suggest a polycyclic epidemic with TSWV secondary spread in the potato crop. Multiple control measures were deduced from these epidemiological results like virus testing in tubers, removal of external virus infection sources and thrips control.     

Laboratory and greenhouse evaluation of a new entomopathogenic strain of Beauveria bassiana for control of the onion thrips Thrips tabaci

Abstract

The onion thrips Thrips tabaci is one of the most important pests of greenhouse and open-field broccoli, onion and other crops. However, the current strategy of using synthetic pesticides for its control is inadequate and unsustainable, leading to a growing interest in novel and effective biological control alternatives such as entomopathogenic fungi. Among 20 isolates of Beauveria bassiana tested for virulence against T. tabaci in laboratory bioassays, we found strain SZ-26 as the most potent, causing 83–100% mortality in adults at 1×10⁷ mL^?1conidia after 4–7 days. Further experiments in greenhouses showed the strain SZ-26 significantly lowered the numbers of adult and larval stages.     

The bumblebee Bombus ardens ardens (Hymenoptera: Apidae) visits white clover in orchards before Oriental persimmon blooms

Flowers on the ground of orchards can provide substantial resources for wild pollinators of orchard trees. Few studies, however, have examined the relative importance of groundcover flowers to orchard pollination by analyzing pollen on the body surface of pollinators. Oriental persimmon trees bloom within the longer blooming period of white clover, which is occasionally found as a flowering plant on the ground of persimmon orchards in Japan. The present study compared the insect species assemblage collected on persimmon flowers with that on clover. Before persimmon bloomed, Bombus ardens ardens and Apis cerana japonica were the major visitors of clover flowers. Once persimmon bloomed, the former was the most abundant bee that visited persimmon flowers over the flowering period. Apis mellifera was captured only on clover flowers. We found numerous clover pollen grains on the body surface of bumblebees captured on persimmon flowers, but far fewer persimmon pollen grains on bees that visited clover. These findings show that B. ardens ardens utilized the clover flowers under the orchards before persimmon bloomed.     

橘园蓟马的种类、发生规律及防治研究

本文以我国柑橘主产区当阳和赣州为试验基地,系统调查了橘园中蓟马为害的严重性及其发生规律;经鉴定发现我国柑橘主产区橘园内蓟马有11种:包括蓟马科中的茶黄蓟马Scirtothrips dorsalis Hood、褐三棕蓟马Lefroyothrips lefroyi(Bagnall)、花蓟马Frankliniella intonsa(Trybom)、八节黄蓟马Thripsflavidulus(Bagnall)、黄胸蓟马T.hawaiiensis(Morgan)、棕榈蓟马T.palmi Karny、色蓟马T.coloratus Schmutz和管蓟马科中的边腹曲管蓟马Rhaebothrips lativentris Karny、华简管蓟马Haplothrips chinensis Priesner、桔简管蓟马H.subtilissimus(Haliday)、狭翅简管蓟马H.tenuipennis Bagnall;并对蓟马进行药剂防治试验,结果表明,吡虫啉、敌百虫和阿维菌素3种药剂都能有效的减少蓟马的虫口数目,在柑橘花期之前和柑橘花期施药可以有效的降低蓟马对果实的为害率。     

Monitoring thrips species with yellow sticky traps in astringent persimmon orchards in Korea

Thrips are one of the insect pests of persimmon (Diospyros kaki Thunb.) in the major production areas of astringent persimmon in Korea. We surveyed astringent persimmon orchards in the Damyang, Sangju and Cheongdo regions of Korea to determine thrips species composition and abundance. Orchards sprayed with either organic or conventional pesticides were sampled over the course of one flowering season, using yellow sticky traps to determine if this is a suitable method for monitoring thrips populations, and to determine thrips species composition and abundance. Eight thrips species were captured on yellow sticky traps in both the tree canopy and ground cover: Ponticulothrips diospyrosi Haga et Okajima, Scirtothrips dorsalis (Hood), Frankliniella occidentalis (Pergande), F. intonsa (Trybom), Thrips tabaci (Lindeman), T. hawaiiensis (Morgan), T. coloratus (Schmutz) and T. palmi (Karny). In all regions, F. occidentalis and F. intonsa dominated in both organic and conventional orchards. S. dorsalis, F. occidentalis, F. intonsa and T. hawaiiensis were found in persimmon flowers, with S. dorsalis the dominant thrips. Significantly more S. dorsalis were captured from flowers in the lower and middle canopy than in flowers from the upper canopy. Fruit damage was also significantly higher in fruit from the lower canopy than in fruit from the middle and upper canopy.     

Does natural deposition of pine pollen affect the ovipositional behavior of Frankliniella occidentalis and Frankliniella fusca?

Tree pollen, especially Pinus spp. (Pinaceae), is shed in large quantities every spring in North America. Pine pollen deposition onto leaves was found to significantly influence the ovipositional behaviors of certain thrips species (Thysanoptera: Thripidae) in peanut and tomato leaf choice and no‐choice tests. Pine pollen (Pinus elliottii Engelm.) increased the oviposition rate 2.9‐fold for Frankliniella occidentalis (Pergande) (western flower thrips) and 1.6‐fold for Frankliniella fusca (Hinds) (tobacco thrips) in choice tests averaged over both plant species. These results support the idea that pollen has a greater impact on F. occidentalis behavior than on F. fusca behavior. The most dramatic increase was in peanut, where F. occidentalis only oviposited on leaves dusted with pollen, suggesting that the addition of pollen stimulated this flower thrips to lay eggs on a poor host‐plant part. The impact of pollen on the rate of oviposition by thrips is important because it is the early‐instar nymphs that acquire tomato spotted wilt virus (TSWV), which these two thrips species vector. In a laboratory bioassay, the addition of pine pollen to TSWV‐infected peanut foliage increased the percentage of infected F. fusca after one generation.