Studies on Kelly's citrus thrips, Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae): sex attractants, host associations and country of origin

Abstract  Under controlled conditions of 25°C and 14 h light, adult Pezothrips kellyanus (Bagnall) were observed to have a peak mating time at 17:00 h, this almost coinciding with the time of minimum feeding. Filter papers on which males had walked attracted both sexes, the attraction being strongest when the odour was collected during the mating period and subsequently offered during this period. Field observations indicate that males aggregate and that females approach such aggregations for mating. In Australia, in the vicinity of citrus orchards, this thrips is associated particularly with non-Australian perfumed white flowers. However, recent collecting indicates that the species is widespread in south-eastern coastal areas far distant from citrus cultivation, in the flowers of an Australian native plant, Myoporum insulare . Despite this host plant evidence, morphological evidence continues to suggest retention of the species in the northern hemisphere genus Pezothrips Karny, and thus the country of origin of the pest remains in doubt.     

Evaluation of phloxine B as a possible control agent against citrus thrips (Thysanoptera: Thripidae)

We evaluated the toxicity of phloxine B photoactive dye combined with a cane molasses bait against citrus thrips, Scirtothrips citri (Moulton). Laboratory bioassays conducted under artificial light showed that thrips mortality followed a log-dose probit-response model with an estimated LC50 of 0.0079% dye. Diluted cane molasses plus 0.01% phloxine B then was used as a standard for comparison of eight additional baits, including three formulations of concentrated citrus peel liquor (CCPL1-3). Citrus thrips mortality ranked highest to lowest with CCPL1 and CCPL3 > CCPL2, Mo-Bait and cane molasses > concentrated beet molasses, concentrated cane molasses, hemicellulose extract, and whey. Several commercial surfactants were tested to see if their addition to the standard increased efficacy. Hyper-Active, Kinetic, and Tween 60 at 1% and Cohort, Hyper-Active, Kinetic, and Silwet at 0.25% when added to the standard, reduced citrus thrips mortality, whereas Tween 60 and Dyne-Amic at 0.25% had no effect. Cane molasses with one or 5% phloxine B dye and CCPL1 with 1% dye were sprayed on citrus trees and allowed to weather in the field. Laboratory bioassays conducted after leaves had weathered for up to 8 d indicated that bait-dye toxicity was persistent. Possible use of the bait-dye mixture in commercial control of citrus thrips is discussed.     

Within-plant distribution of onion thrips (Thysanoptera: Thripidae) in onions

Two aspects of the within-plant distribution of Thrips tabaci Lindeman (Thysanoptera: Thripidae) on onion, Allium cepa L., plants were investigated: 1) diurnal variations in the distribution of adults and larvae between basal and upper sections of onion leaves, and 2) between-leaf and within-leaf distribution of the eggs. The diurnal investigations showed that higher proportions of larvae than of adults congregated at the basal sections of plants, particularly when plants were young and thrips density was low. As plants matured and thrips density increased, the larvae became more dispersed. Regardless of plant size, there were always more adults in the upper than basal plant sections. There were no clear time-windows during the 24-h diurnal cycle when more thrips were in the upper plant parts. T. tabaci eggs were laid everywhere in the plant. Leaves of intermediate ages had more eggs than older or younger leaves. Within leaves, the white leaf sheath received the least eggs and leaf tips received slightly more eggs than leaf sheaths. The highest egg density was found between the green leaf base and the leaf tips. Regardless of plant size, more than half of all eggs were laid above the basal sections. The percentage increased to >95% in mature plants. Except when plants were small the outer leaves were preferred over inner leaves and upper leaf sections preferred over lower leaf sections as egg-laying sites by adults. Implications of the results in the management of T. tabaci are discussed.     

Sampling techniques for thrips (Thysanoptera: Thripidae) in preflowering tomato

Sampling techniques for thrips (Thysanoptera: Thripidae) were compared in preflowering tomato plants at the Coastal Plain Experiment Station in Tifton, GA, in 2000 and 2003, to determine the most effective method of determining abundance of thrips on tomato foliage early in the growing season. Three relative sampling techniques, including a standard insect aspirator, a 946-ml beat cup, and an insect vacuum device, were compared for accuracy to an absolute method and to themselves for precision and efficiency of sampling thrips. Thrips counts of all relative sampling methods were highly correlated (R > 0.92) to the absolute method. The aspirator method was the most accurate compared with the absolute sample according to regression analysis in 2000. In 2003, all sampling methods were considered accurate according to Dunnett's test, but thrips numbers were lower and sample variation was greater than in 2000. In 2000, the beat cup method had the lowest relative variation (RV) or best precision, at 1 and 8 d after transplant (DAT). Only the beat cup method had RV values <25 for all sampling dates. In 2003, the beat cup method had the lowest RV value at 15 and 21 DAT. The beat cup method also was the most efficient method for all sample dates in both years. Frankliniella fusca (Pergande) was the most abundant thrips species on the foliage of preflowering tomato in both years of study at this location. Overall, the best thrips sampling technique tested was the beat cup method in terms of precision and sampling efficiency.     

Advances in control of onion thrips (Thysanoptera: Thripidae) in cabbage

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), feeding injury results in discoloration and a rough texture on cabbage, Brassica oleracea capitata (L.), leaves, and damage may occur deep inside the head. It has become a key pest of cabbage in the United States and many other countries. Previous studies have indicated poor control using insecticides. The present study identified imidacloprid drenches and sprays of acetamiprid, dimethoate, spinosad, and imidacloprid as insecticides that performed better than the industry standard, lambda-cyhalothrin. However, additional tests with foliar sprays of dimethoate and acetamiprid indicated there was not an ideal crop stage (precupping, cupping, or postcupping) at which either insecticide could be applied for reliable control of T. tabaci, possibly because of multiple flights of thrips into the crop or the asynchrony of flights and susceptible crop stages. In tests in a commercial field, a soil drench of imidacloprid 4 wk after transplanting reduced the number of damaged leaves in the head by 32%, whereas five sprays of acetamiprid reduced damage by 51%. Combining both insecticide regimes reduced damage by 85%, but resulted in a very costly management program. Cabbage varieties varied considerably in susceptibility with some having negligible thrips injury, regardless of being treated with an insecticide. Planting date affected susceptibility of cabbage to some degree, but not as much as other tactics. Overall, these studies indicate that increased emphasis should be placed on breeding cabbages to be resistant to T. tabaci as the foundation for its management.     

Temperature-mediated relationship between western flower thrips (Thysanoptera: Thripidae) and chrysanthemum

Modeling the effect of temperature on the sustainability of insect-plant interactions requires assessment of both insect and plant performance. We examined the effect of temperature on western flower thrips, Frankliniella occidentalis (Pergande), a generalist herbivore with a high reproductive rate, and chrysanthemum inflorescences, a high quality but relatively fixed, ephemeral resource for thrips population growth. We hypothesized that different thrips versus plant responses to temperature result in significant statistical interaction of temperature with thrips abundance and flower damage attributes over time. Experiments were conducted at five temperatures between 20.7 and 35.3 degrees C, with thrips infestation and time after infestation as main effects. Only minor, uncontrolled variations in relative humidity and light intensity may otherwise have influenced the results. High temperatures lead to an initially rapid increase in density of thrips followed by abrupt declines in abundance. The rate of floral senescence increased with temperature and thrips infestation, as indicated by a reduced fresh biomass and greater leaching of yellow pigments. Multiple regression indicated that indices of plant damage responded more directly to thrips density at low than high temperature, supporting the conclusion that temperature affected the outcome beyond what was predictable simply from differential plant and insect optima. The relative intensity of damage caused by individual thrips decreased with increasing temperature, likely caused by thrips competition and reduced survival, growth, and fecundity on depleted inflorescences. Reduced per capita damage at high temperature may be common in insects exploiting fixed plant resources that exhibit an accelerated rate of deterioration at high temperatures.     

Integrated management tactics for Frankliniella thrips (Thysanoptera: Thripidae) in field-grown pepper

In a 2-yr study, the impacts of different plastic soil mulches, insecticides, and predator releases on Frankliniella thrips and their natural enemies were investigated in field-grown peppers. Ultraviolet light (UV)-reflective mulch significantly reduced early season abundance of adult thrips compared with standard black plastic mulch. This difference diminished as the growing seasons progressed. Late season abundance of thrips larvae was higher in UV reflective mulch compared with black mulch plots. The abundance of the predator Orius insidiosus (Say) was significantly lower in UV-reflective mulch compared with black mulch treatments. Infection of plants with tomato spotted wilt virus, a pathogen vectored by Frankliniella occidentalis (Pergande), was <6%. In the year with the higher disease incidence (2000), UV-reflective mulch plots had significantly less disease (1.9%) compared with black mulch plots (4.4%). Yield was significantly higher in UV-reflective mulch (24,529 kg/ha) compared with black mulch (15,315 kg/ha) during this year. Effects of insecticides varied with species of thrips. Spinosad reduced abundance of F. occidentalis, but not Frankliniella tritici. In contrast, esfenvalerate and acephate reduced numbers of F. tritici and Frankliniella bispinosa, but resulted in higher populations of F. occidentalis. Spinosad was the least disruptive insecticide to populations of O. insidiosus. Releases of O. insidiosus and Geocoris punctipes (Say) reduced populations of thrips immediately after releases; naturally occurring predators probably provided late season control of thrips. Our results suggest that UV-reflective mulch, combined with early season applications of spinosad, can effectively reduce abundance of thrips in field-grown pepper.     

Economic injury levels for western flower thrips (Thysanoptera: Thripidae) on greenhouse cucumber

Low, medium and high densities of western flower thrips, Frankliniella occidentalis (Pergande), were established in three greenhouses at the Greenhouse and Processing Crops Research Centre, Ontario, Canada, in 1996 and 1998 to develop economic injury levels for thrips on greenhouse cucumber. Thrips densities were monitored weekly using yellow sticky traps and flower counts. Fruit was harvested twice a week, graded for size, weighed, and rated for thrips damage using three damage categories. Significant yield reduction was detected 4 wk after severe fruit damage was observed in the high and medium thrips density treatments in 1996 and 7 wk in 1998. Percentage of severe damaged fruit (P(F3)) has significant linear relationships with the adult thrips density (x) that was sampled by sticky traps 1 wk before harvest (P(F3) = -0.2533 + 0.0828x) and that was sampled by flower counts 2 wk before harvest (P(F3) = -0.2025 + 0.5490x). Based on the regression equations, economic injury levels, expressed as adult thrips per sticky trap per day or adult thrips per flower, were calculated for various combinations of control costs, yield potential and fruit prices. The economic injury levels for F. occidentalis ranged from 20 to 50 adults per sticky trap per day or 3 to 7.5 per flower as determined under average greenhouse production conditions in Ontario, Canada.     

Sequential sampling plans for western flower thrips (Thysanoptera: Thripidae) on greenhouse cucumbers

The development of cost-effective and reliable sampling programs for the management of western flower thrips, Frankliniella occidentalis (Pergande), on greenhouse cucumbers is important for getting growers to adopt economic injury levels and economic thresholds. The objectives of this study were to develop two sequential sampling plans. A fixed-precision sequential sampling plan was designed for estimating F. occidentalis adult density at a fixed-precision level on cucumber flowers. Also, a sequential sampling plan for classifying thrips population levels as below or above economic thresholds was developed to assist in decision making for the timing of pesticide applications. Both sequential sampling plans were validated using a resampling simulation technique on nine independent data sets ranging in density from 1.25 to 12.95 adults per flower. With the fixed-precision sampling plan, average means obtained in 100 repeated simulation runs were within the 95% CI of the estimated mean for all data sets. Appropriate levels of precision for the different population densities were recommended based on the simulation results. With sequential sampling for classifying the population levels of thrips in terms of an economic threshold, it has the advantage of requiring smaller sample sizes to determine the population status when the population densities differ greatly from the critical density (i.e., economic threshold). However, this plan needs a great number of samples when population density is close to the critical density. In this case, use of a combination of both sampling plans is recommended.     

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.     

Life-stage variation in insecticide resistance of the western flower thrips (Thysanoptera: Thripidae)

The life-stage variations in insecticide resistance of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), to selective insecticides (acrinathrin, formetanate, and methiocarb) were studied using resistant laboratory strains. In each strain, the second-instar larva was less susceptible to the insecticides tested than the adults. The lower the resistance level of the adults, the higher the difference between larva and adult susceptibility: 32-fold to methiocarb, 15.4-fold to formetanate, and 180-fold to acrinathrin in the reference strain. In laboratory-selected resistant strains, these differences were much lower: 5.8-fold to methiocarb, 4.8-fold to formetanate, and 2.0-fold to acrinathrin. In selected strains, higher resistance levels for each insecticide were found, both for larvae and adults, compared with the reference strain. These results show that after insecticide resistance selection in adults, the resistance is carried over to the larvae, but at lower levels.     

The distribution and abundance of phytoseiid mites (Acari: Phytoseiidae) on citrus in southern Africa and their possible value as predators of citrus thrips (Thysanoptera: Thripidae)

On citrus in Zimbabwe, Swaziland and South Africa, predacious mites of the subfamily Amblyseiinae are more common and found in greater numbers than phytoseiids of the subfamily Phytosciinae. The author's survey and other collection data indicated that within the Amblyseiinae the genus Euseius Wainstein is the most widely distributed. Seven Euseius spp. have been recorded on citrus in the above countries but not more than one species has been found at any particular site and time. E. citri (Van der Merwe and Ryke) has the broadest geographical distribution and is capable of suppressing population levels of the citrus thrips Scirtothrips aurantii Faure. However, it is not as effective a biocontrol agent as E. addoensis (Van der Merwe and Ryke) which occurs in higher numbers further south. An orchard comparison of the non-target effects of thripicides showed that E. citri was more susceptible to sabadilla alkaloids (0.0024% AI) plus sugar (0.96%) than to tartar emetic (0.398% AI) plus sugar (0.4%). The author's survey provides the first records of E. orygmus (Ueckermann and Loots) and E. tutsi (Pritchard and Baker) on citrus in Zimbabwe. Typhlodromalus Muma spp. were not widely distributed but where they did occur they were often abundant and sometimes coexisted with Euseius spp. Circumstantial evidence indicated that Typhlodromalus spp. may be effective thrips predators. The combination of Euseius and Typhlodromalus spp. may provide more effective biological control of citrus thrips than either species alone. Amblydromella Muma spp. were the only representatives of the subfamily Phytoseiinac currently found on citrus and they occurred only in the Transvaal and Natal provinces of South Africa. The possibility that Amblydromella spp. compete with Amblyseiinae is discussed.     

Modern thrips families Thripidae and Phlaeothripidae in Early Cretaceous amber (Insecta: Thysanoptera)

Two specimens of Thysanoptera with forked sensilla on third and fourth antennal segments were described from the Lebanese Neocomian and the Spanish Albian ambers, and attributed to the new genus Tethysthrips n. gen. in the family Thripidae Stevens 1829. One specimen with a tubular tenth abdominal segment was also discovered in the Lebanese Neocomian amber, and attributed to the new genus Rohrthrips n. gen. belonging to the family Phlaeothripidae Uzel 1895. Thripidae and Phlaeothripidae are nowadays the most species-rich families of Thysanoptera. The present discoveries of Early Cretaceous fossils show how diversified these families and thrips already were at that time. Moreover, this tubuliferan Rohrthrips specimen has plesiomorphies no longer present in the recent genera, in particular on the wings. Therefore it brings new insight in the evolution of Tubulifera.     

Onion thrips (Thysanoptera: Thripidae): a global pest of increasing concern in onion

During the past two decades, onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), has become a global pest of increasing concern in commercial onion (Allium cepa L.), because of its development of resistance to insecticides, ability to transmit plant pathogens, and frequency of producing more generations at high temperatures. T. tabaci feeds directly on leaves, causing blotches and premature senescence as well as distorted and undersized bulbs. T. tabaci can cause yield loss > 50% but can be even more problematic when it transmits Iris yellow spot virus (family Bunyaviridae, genus Tospovirus, IYSV). IYSV was identified in 1981 in Brazil and has spread to many important onion-producing regions of the world, including several U.S. states. IYSV symptoms include straw-colored, dry, tan, spindle- or diamond-shaped lesions on the leaves and scapes of onion plants and can cause yield loss up to 100%. Here, we review the biology and ecology of T. tabaci and discuss current management strategies based on chemical, biological, and cultural control as well as host resistance. Future directions for research in integrated pest management are examined and discussed.     

Systemic effects of neem on western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae)

The systemic effects of neem on the western flower thrips, Frankliniella occidentalis (Pergande), were investigated in laboratory trials using green bean, Phaseolus vulgaris L., in arena and microcosm experiments. In arena experiments, systemic effects of neem against western flower thrips larvae on primary bean leaves were observed with maximum corrected mortality of 50.6%. In microcosm experiments using bean seedlings, higher efficacy in the control of western flower thrips were observed with soil applications of neem on a substrate mixture (i.e., Fruhstorfer Erde, Type P, and sand) in a 1:1 ratio (93% corrected mortality) compared with application on the commercial substrate only (76% corrected mortality). However, longer persistence of neem was observed with soil application on the commercial substrate, which showed effects against thrips for up to 6 d after application. In addition to systemic effects observed on all foliage-feeding stages of western flower thrips, mortality on contact and repellent effects were observed on soil-inhabiting stages after soil applications of neem. Finally, bean seedlings grown from seeds pregerminated for 3 d in neem emulsion were also toxic to western flower thrips.     

Inheritance of vector competence by the thrips Ceratothripoides claratris (Shumsher) (Thysanoptera: Thripidae)

The thrips Ceratothripoides claratris is an efficient vector of the Capsicum chlorosis virus (CaCV). Transmission studies with a natural population of C. claratris found in a greenhouse ‘GH’ and a ‘colony’ derived from this ‘GH’ population by selection and inbreeding resulted in lowering the percentage of viruliferous individuals within the ‘colony’. After passing through approximately 20 generations, the ‘colony’ lost the ability to transmit the CaCV. When either viruliferous or non‐viruliferous virgin females reproduced parthenogenetically, 81% of F1 arrhenotokous males inherited their viruliferous status from their mothers, whilst, no viruliferous offspring arose from non‐viruliferous virgin mothers. Crosses between viruliferous and non‐viruliferous individuals suggest that the competence of the thrips C. claratris as a vector for this virus is probably a heritable trait controlled by a recessive allele.     

Efficacy of biorational insecticides against chilli thrips,Scirtothrips dorsalis (Thysanoptera: Thripidae), infesting roses under nursery conditions

We evaluated biopesticides based on entomopathogenic fungi, azadirachtin and horticultural oils for the management of the chilli thrips, Scirtothrips dorsalis Hood, an economically significant invasive pest in the United States. Insecticides were applied four times at 7‐ to 10‐day intervals against established S. dorsalis infestations on shrub roses KnockOut^®, Rosa x ‘Radrazz’ under simulated nursery conditions. When applied as stand‐alone treatments, Beauveria bassiana GHA (BotaniGard^® ES), Metarhizium brunneum F52 (Met‐52 EC), a horticultural oil (SuffOil‐X^®) and azadirachtin (Molt‐X^®) at label rates provided significant control, reducing populations of S. dorsalis by 48–71% compared with control over 4–6 weeks. Similar results were observed when the biopesticides were applied in rotation with each other. A conventional standard, spinosad (Conserve^® SC), was consistently the most effective treatment in these studies, reducing thrips populations by >95% overall. In another study, more effective control (87%–92%) was achieved in biopesticide rotation programmes that included spinosad, when compared with those that did not. Results also showed that these biopesticides can be tank‐mixed. However, there was no evidence that B. bassiana or M. brunneum combined with azadirachtin resulted in additive or synergistic control, as neither tank‐mix treatment improved control compared with azadirachtin alone. These findings highlight the potential use of biopesticides in rotation programmes with conventional insecticides to manage S. dorsalis on roses. Biopesticides evaluated in this study can be incorporated into an IPM programme for roses.     

不同施钾水平对苜蓿营养物质及抗蓟马性的影响

【目的】明确施钾是否能有效提高苜蓿对蓟马的抗性以及钾-营养物质-抗虫性之间的关系。【方法】以感蓟马紫花苜蓿Medicago sativa品种甘农3号(Gannong No.3)和抗蓟马紫花苜蓿品种甘农9号(Gannong No.9)为材料,设0,6,9,12和15 g/m2(K2O)5个钾水平,在大田蓟马为害高峰期,评价和测定了不同钾水平处理下苜蓿的受害指数、虫口数量、叶片钾含量、碳氮比和游离氨基酸变化。【结果】在第2茬中,随着钾水平的升高,甘农3号和甘农9号老叶和心叶的钾含量上升,可溶性糖和碳氮比升高,游离氨基酸含量下降,虫口数量无显著性差异,受害指数显著降低(P0.05),且在9 g/m2(K2O)水平下最低。在第3茬中,甘农3号和甘农9号的受害指数、叶片钾含量、碳氮比及游离氨基酸的变化规律和第2茬相同,但虫口数量上升。第2茬和第3茬中,不同施钾水平下,苜蓿叶片钾含量与受害指数负相关但不显著(P0.05)。施钾后甘农3号的受害指数均低于未施钾甘农9号的受害指数。【结论】钾元素可通过提高苜蓿碳氮比,降低游离氨基酸的含量来提高苜蓿对蓟马的耐害性。在大田条件下,通过施钾管理来提高苜蓿品种对蓟马的耐害性是一种有效的措施。     

Population dynamics of western flower thrips (Thysanoptera: Thripidae) in nectarine orchards in British Columbia

Development of a control strategy for thrips attacking nectarine trees depends on an understanding of their phenology, distribution, and life history as related to characteristics of nectarine orchards. To this end, we compared the overwintering behavior, distribution, and abundance of western flower thrips, Frankliniella occidentalis (Pergande), among 11 nectarine orchards located in the dry central interior of British Columbia, Canada, during 1993 and 1994. Western flower thrips emerged from areas not previously used for agriculture (wild areas) and from within orchards before trees were out of dormancy. Flight of thrips within and around orchards peaked during early bud development, with a second major peak several weeks later after husk fall as the next generation emerged. Orchards protected from wild areas by other orchards had the lowest densities of thrips in buds. Density estimates of western flower thrips on trees were not affected by location of trees within orchards or buds within trees, but most thrips were found in the most developed buds on a tree at any one time. Thrips were not found within buds until petal was first visible on the buds. Larval feeding on buds at early petal fall resulted in serious surface russetting of fruit.