Distribution Of Thrips Research Articles

Prediction of Thrips Damage Distribution in Mango Orchards Using a Novel Maximum Likelihood Classifier

Thrips constitute the primary pest responsible for reducing mango yield and quality every year in Asia. Therefore, the efficient monitoring of thrips damage across mango orchards on a large scale to aid farmers in devising rational pesticide application strategies poses a significant challenge within the current mango industry. This study designs a mango thrips damage inversion prediction method based on the maximum likelihood classifier (MLC). Initially, drone multispectral remote sensing technology is utilized to acquire multispectral data from mango orchards, which are then combined with ground hyperspectral information to identify sensitive bands indicative of mango leaf damage caused by thrips. Subsequently, correlation analysis is conducted on various vegetation indices, leading to the selection of the Greenness Normalized Difference Vegetation Index (GNDVI), which exhibits a strong correlation coefficient of 0.82, as the spectral characteristic parameter for the inversion prediction model. The construction of a remote sensing prediction model for thrips damage distribution in mango orchards is then undertaken based on the MLC. Acknowledging the bias-variance trade-off inherent in the MLC when processing spectral data and its potential limitations in feature extraction and robustness, this study proposes a modification wherein neighboring pixels are weighted differently to enhance the model’s feature extraction capabilities. Experimental results show that the novel MLC maintains stable estimation levels across various numbers of domain pixels, achieving an inversion accuracy of 91.23%. Through the reconstruction of the pixel matrix, the damage distribution of thrips in mango orchards can be swiftly and comprehensively visualized over extensive areas.

Whether curse or blessing: A counterintuitive perspective on global pest thrips infestation under climatic change with implications to agricultural economics

The improvement and application of pest models to predict yield losses is still a challenge for the scientific community. However, pest models were targeted chiefly towards scheduling scouting or pesticide applications to deal with pest infestation. Thysanoptera (thrips) significantly impact the productivity of many economically important crops worldwide. Until now, no comprehensive study is available on the global distribution of pest thrips, as well as on the extent of cropland vulnerability worldwide. Further, nothing is known about the climate change impacts on these insects. Thus the present study was designed to map the global distribution and quantify the extent of cropland vulnerability in the present and future climate scenarios using data of identified pest thrips within the genus, i.e., Thrips, Frankliniella, and Scirtothrips. Our found significant niche contraction under the climate change scenarios and thrips may reside primarily in their thermal tolerance thresholds. About 3,98,160 km2 of cropland globally was found to be affected in the present scenario. However, it may significantly reduce to 5530 Km2 by 2050 and 1990 km2 by 2070. Further, the thrips distribution mostly getting restricted to Eastern North America, the North-western of the Indian sub-continent, and the north of Europe. Among all realms, thrips may lose ground in the Indo-Malayan realm at the most and get restricted to only 27 out of 825 terrestrial ecoregions. The agrarian communities of the infested regions may get benefit if these pests get wiped out, but on the contrary, we may lose species diversity. Moreover, the vacated niche may attract other invasive species, which may seriously impact the species composition and agricultural productivity. The present study findings can be used in making informed decisions about prioritizing future economic and research investments on the thrips in light of anticipated climate change impacts.

Onion Germplasm Possesses Lower Early Season Thrips Numbers

Onion is one of the most valuable vegetable crops in the US. Onion thrips were identified as one of the main threats to the US onion industry. An integrated approach, including host plant tolerance, is required. For this study, four New Mexico State University breeding lines, along with two thrips-attractive cultivars, were evaluated for their attractiveness to thrips. In addition, this study observed thrips population dynamics throughout the growing season and the relationship between onion plant size and thrips attractiveness. The experiment was designed as a randomized complete block design with three blocks, each containing four replications. Thrips-infested bulbs were used to ensure the presence of thrips and thrips-attractive plants were used to ensure equal thrips distribution throughout the field. Ten plants were randomly selected from each plot and thrips and leaf numbers were counted multiple times through the growing season. Plants of NMSU breeding lines were observed to have fewer thrips, be more tolerant to thrips pressure and produce more leaves and larger bulbs than thrips-attractive entries. Early in the growing season, leaf number was not a determining factor in thrips population dynamics. The larger bulb weights of the breeding lines allowed them to maintain their market value. A delay in thrips population buildup in plants of the breeding lines may result in the critical threshold for spraying for thrips being reached later in these lines. This would potentially allow for fewer pesticide applications by growers, increasing growers’ profits and ensuring a more environmentally friendly approach to plant production.

Checklist of the suborder Terebrantia (Thysanoptera): generic diversity and species composition in Xishuangbanna, Yunnan Province, China.

BackgroundThysanoptera is amongst the most predominant orders of insects in different ecological zones with worldwide distribution. Due to their small size, there is a large gap in their distribution and host range data. To the best of our knowledge, there is no investigation on the thrips distribution and their host range in Xishuangbanna. Currently, a total of 566 species in 155 genera are listed in China, of which 313 species represent Terebrantia.New informationIn this study, a list of 116 species representing 55 genera within the families Aeolothripidae and Thripidae is provided. Two of these, Dichromomothripsnakahari Moud, 1976 (subfamily Thripinae) and Phibalothripsrugosus Kudo, 1979 (subfamily Panchaetothripinae) are recorded for the first time in China. Thrips species with their host ranges, habits and habitats are provided. Our study aims to contribute to the global biodiversity distribution data-gap of Thysanoptera for conservation purposes, as well as pest species targetting Integrated Pest Management tactics.

Attractiveness of Different Coloured Sticky Traps to the South African Citrus Thrips (Scirtothrips aurantii Faure) in Avocado, KwaZulu-Natal, South Africa

The South African citrus thrips, Scirtothrips aurantii, is a recently confirmed economic pest in South African avocado. Scarring damage by thrips results in corky tissue development, making the fruit unsuitable for export and potentially costing the country in lost export revenue. Thrips management is complicated by the multiple and protracted flowering patterns of susceptible cultivars. In addition, widespread pesticide resistance of thrips and the negative environmental effects along with minimum residue levels for export fruit limit the application of pesticides for thrips control. Monitoring an insect pest's presence and abundance is the first step in thrips management. This study aimed to investigate S. aurantii's colour preferences, establish the distribution of thrips in the orchard and population dynamics from flowering to fruit establishment. Attractiveness followed the order yellow > blue, white, clear > red, black, purple and orange. Thrips were evenly distributed throughout the orchard, with the highest populations occurring during flowering (August), declining sharply and picking up in the summer months starting December. Yellow sticky cards are recommended as a monitoring tool.

Species composition and distribution of thrips (Thysanoptera) in mango orchards of China

Abstract Mango is an important tropical fruit, and thrips are important pests that have threatened mango yield and quality in recent years. It is important to determine the dominant species and distribution of thrips in mango for effective thrips control. In the present study, the species of thrips in mango flowers in the five main mango-producing provinces of China, and the species of thrips in different phenological stages of mango in Hainan Province were investigated. Thrips species on weeds in mango agroecosystems were also determined. The results indicated that in total there are 41 species of thrips in mango orchards in the five main mango-producing provinces of China, belonging to 21 genera, five subfamilies and three families. These are 31 species in 13 genera of Thripidae, nine species in seven genera of Phlaeothripidae, and one species in one genus of Aeolothripidae. The major species of thrips differed across the main mango production areas. Thus, 26, 17, 23, 12 and 7 species of thrips were collected in mango orchards in Hainan, Guangxi, Yunnan, Sichuan and Fujian, respectively. Frankliniella occidentalis (Pergande), an important invasive pest in China, was only discovered in mango orchards in Yunnan and Sichuan. Thrips species and population dynamics are closely related to the phenological stage of mango. In Hainan, the dominant thrips species during the shoot period and young fruit stage was Scirtothrips dorsalis Hood. In the flowering period, the thrips population increased significantly and species composition became complicated in the field, with Thrips hawaiiensis and F. intonsa being the dominant species. Frankliniella intonsa and T. hawaiiensis were the dominant species on weeds in the mango ecosystem, which was consistent with them being dominant thrips species on mango. It is speculated that in mango ecosystems, weeds provide refuge to thrips and removing weeds benefits thrips control in mango orchards during the flowering period.

Mapeo de la distribución espacial de trips (Insecta:Thysanoptera) en parcelas comerciales de aguacate Var. Hass en Coatepec Harinas, Estado de México

Maldonado, F.I., Ramirez, J.F., Lara, A.V., Acosta, D.A., Rivera, R., Tapia Reyes, A. 2017. Mapping of the spatial distribution of thrips (Insecta: Thysanoptera) in commercial plots of avocado Var. Hass in Coatepec Harinas, State of Mexico. Ecosistemas 26(2): 52-60. Doi.: 10.7818/ECOS.2017.26-2.06 The present study allowed to know the spatial distribution of thrips through density maps in three commercial plots of avocado in Coatepec Harinas, State of Mexico. The results showed that for the period from July to December 2015, the spatial distribution of thrips was adjusted to gaussian models in their entirety with an infested surface that oscillated between 90 and 100% showing an aggregated spatial distribution; The nugget effect obtained for all the samples corroborated the aggregation of thrips populations and referred to a minimum sampling error for the twelve samplings performed. Works such as this, in which geostatistical methods are applied, contribute to the knowledge of phytosanitary problems of crops of economic importance and to the application of control measures (chemical, biological, cultural or mechanical) directed to specific areas of the plot.

A Rapid Sampling Plan for Scirtothrips dorsalis (Thysanoptera: Thripidae) on Container Shrub Rose (Rosa 'Radrazz').

The development of simple and reliable pest sampling programs is needed for growers to adopt economic or aesthetic injury levels. We developed a sampling plan for monitoring chilli thrips Scirtothrips dorsalis Hood populations on KnockOut shrub roses under simulated nursery conditions. The distribution of S. dorsalis among different plant structures revealed that most adults and larvae are found on foliar terminals, when compared with buds and flowers. Based on thrips distribution, the third leaf of actively growing terminals was used to determine a sequential sampling model. Thrips had an aggregated distribution, based on Taylor's power law and Iwao's mean crowding index, with both models showing a good fit (i.e., R2 of ∼0.8 and ∼0.9, respectively). Based on these model parameters, the number of samples required to estimate populations with a 10% precision was ∼30 leaves according to Green's and Kuno's enumerative sequential sampling plans. A binomial model also estimated the proportion of infested leaf terminals as a function of insect density with an R2 value of 0.85. An additional study demonstrated that correlation between visual damage to the third leaf terminal and initial thrips populations was modeled by simple power functions. This finding suggests that a more rapid visual sampling of plant damage can be used to indirectly estimate S. dorsalis populations. Our sampling plan provides a tool to monitor S. dorsalis populations that could be used to help make management decisions for this pest in commercial nurseries.

Leaf trichomes and foliar chemistry mediate defence against glasshouse thrips; Heliothrips haemorrhoidalis (Bouché) in Rhododendron simsii.

Herbivore defence mechanisms are a costly diversion of resources away from growth and reproduction. Thus time-limited and tissue specific expression in critical plant parts is more efficient as defined by optimal defence theory. Surprisingly little is known about Rhododendron herbivore defence but it may be mediated by combined chemical and physical mechanisms. Rhododendron simsii Planch. survives cyclic infestations of a leaf-feeding thrips, Heliothrips haemorrhoidalis (Bouché), which severely damage mature leaves but avoid terminal young leaves suggesting specific, localised defence expression. We examined correlations between the distribution of thrips and feeding damage with density of trichomes and the concentration of the diterpenoid, grayanotoxin I, a compound implicated in but not previously reported to mediate invertebrate defence in Rhododendron. Our data show that as leaves matured the number of thrips and area of feeding damage increased as trichome density and grayanotoxin I concentration decreased, this inverse correlation suggesting trichomes and grayanotoxin I mediate defence in younger leaf tissue. Grayanotoxin I was tested against H. haemorrhoidalis and was toxic to immature life stages and repellent to the adult thrips, reducing numbers of first instars emerging on leaves when applied at ecologically relevant concentrations. This work demonstrates that the pattern of defensive traits in foliage of a species of Rhododendron is key to its ability to tolerate cyclic infestations of a generalist herbivore, effectively conserving vital tissues required for growth and reproduction.

Within-Crop Air Temperature and Humidity Outcomes on Spatio-Temporal Distribution of the Key Rose Pest Frankliniella occidentalis.

Frankliniella occidentalis (Pergande) is a key pest of various crops worldwide. In this study, we analyse the dependence of the infestation of this pest on spatially distributed micro climatic factors in a rose greenhouse. Despite the importance of this subject, the few existing studies have been realized in laboratory rather than in greenhouse conditions. However, recent progress on greenhouse microclimate characterisation has highlighted the strong indoor climate heterogeneity that may influence the within-crop pest distribution. In this study, both microclimate (air temperature and humidity) and thrips distribution were simultaneously mapped in a rose greenhouse. The measurements were sensed in a horizontal plane situated at mid-height of the rose crop inside the greenhouse. Simultaneously, thrips population dynamics were assessed after an artificial and homogeneous infestation of the rose crop. The spatio-temporal distribution of climate and thrips within the greenhouse were compared, and links between thrips infestation and climatic conditions were investigated. A statistical model was used to define the favourable climate conditions for thrips adults and larvae. Our results showed that (i) the air temperature and air humidity were very heterogeneously distributed within the crop, (ii) pest populations aggregated in the most favourable climatic areas and (iii) the highest population density of thrips adults and larvae were recorded at 27°C and 22°C for temperature and 63% and 86% for humidity, respectively. These findings confirm, in real rose cropping conditions, previous laboratory studies on the F. occidentalis climatic optimum and provide a solid scientific support for climatic-based control methods against this pest.

Flight movement and spatial distribution of immunomarked thrips in onion, potato, and tomato

The objective of this work was to evaluate the spatial distribution of thrips in different crops, and the correlation between meterological parameters and the flight movements of this pest, using immunomarking. The experiment was conducted in cultivated areas, with tomato (Solanum lycopersicum), potato (Solanum tuberosum), and onion (Allium cepa); and non-cultivated areas, with weedy plants. The areas with tomato (100 days), potato (20 days), and weeds were sprayed with casein, albumin, and soy milk, respectively, to mark adult thrips; however, the areas with onion (50 days) and tomato (10 days) were not sprayed. Thrips were captured with georeferenced blue sticky traps, transferred into tubes, and identified by treatment area with the Elisa test. The dependence between the samples and the capture distance was determined using geostatistics. Meteorlogical parameters were correlated with thrips density in each area. The three protein types used for immunomarking were detected in different proportions in the thrips. There was a correlation between casein-marked thrips and wind speed. The thrips flew a maximum distance of 3.5 km and dispersed from the older (tomato) to the younger crops (potato). The immunomarking method is efficient to mark large quantities of thrips.

A qualitative and quantitative study of thrips (Thysanoptera) on alfalfa and records of thrips species on cultivated and wild Medicago species of Greece

AbstractFoliage and litter samples of twelve Medicago species (medics) (Fabaceae) were collected for the study of Thysanoptera from mainland and insular Greece between 2007-2013. The species composition, population dynamics and spatial distribution of thrips were also evaluated based on two similarly managed experimental plots, except the number of cuttings, within an alfalfa hay field in Kopais Valley (Central Greece) between 2007-2008. Nine thrips species were recorded from nine medics, two of which (Pseudodendrothrips mori and Sericothrips bicornis) are new to the Greek fauna. Eight species of Thysanoptera were recorded on alfalfa and five species in the rest of the medics, among which Medicago strasseri is an endemic shrub of Crete. Data regarding the quantitative part of the study demonstrated that Frankliniella occidentalis, which was the most abundant thrips species in both plots, presented a seasonal pattern of population fluctuation and also tended to aggregate. The mean population density of this species significantly differed between the above-mentioned plots, but no such a difference was estimated for the larvae of Thripidae.

Population ecology of Thrips palmi (Thysanoptera:Thripidae) in orchid farms in Thailand

The population dynamics and in-farm distribution of Thrips palmi Karny were evaluated in two orchid farms, one in the Bangkok metropolitan area and the other in Ratchaburi Province, Thailand. Yellow sticky traps were hung above the orchid canopy (three traps/220 m2), and the trapped adults were counted weekly from November 2009 to October 2010 at the first location and from January to December of 2012 at the second location. T. palmi nymphs and adults were both counted weekly on 300 orchid panicles in an area of 2,200 m2 at both locations. We found that the T. palmi population dynamics at the first location was represented by a W-shaped curve, with the distribution clumped throughout the year, whereas the curve was J-shaped at the second location, with the distribution mostly clumped. Qualitative surveys of thrips species were conducted on ten different orchid genera in ten locations and on 20 different Dendrobium hybrids in 20 locations. Five random sampling plots (1 × 4 m2) were examined on each farm. The results indicated that only T. palmi was found on every farm. Moreover, quantitative comparison among five orchid types revealed that Dendrobium flowers with darker color are more attractive to T. palmi. However, this phenomenon does not coincide with Oncidium sp. and Mokara sp. because of their unfavorable morphology for thrips behavior.

DEPENDENCE OF THRIPS INFESTATION ON SPATIAL CLIMATE DISTRIBUTION IN A ROSE GREENHOUSE CROP

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Greenhouse 2010 and Soilless Cultivation DEPENDENCE OF THRIPS INFESTATION ON SPATIAL CLIMATE DISTRIBUTION IN A ROSE GREENHOUSE CROP

Color preference, seasonality, spatial distribution and species composition of thrips (Thysanoptera: Thripidae) in northern highbush blueberries

We investigated color preference, seasonal abundance, spatial distribution and species composition of thrips in northern highbush blueberries, Vaccinium corymbosum L., in New Jersey (USA). White sticky traps were more attractive to thrips compared with yellow or blue traps. Thrips captures using white sticky traps showed that their flight activity begins 20–30 d after the onset of flowering, with 10, 50 and 90% of trap captures observed at 383, 647 and 1231 degree-day accumulations, respectively (10 °C base temperature). Two methods were used to study thrips distribution within a blueberry bush. First, white sticky traps were placed within the bush canopy at three different heights. The highest numbers of thrips were caught on traps in the middle and top one-third of the canopy while the lowest numbers were caught in the bottom one-third. A second method determined the distribution of thrips on the blueberry plant at different heights and phenological stages. The highest numbers of thrips were found on young leaves at lower parts of the canopy, whereas flowers and fruit had fewer thrips and none were found on buds; these thrips were identified as, Scirtothrips ruthveni (88% of adults) and Frankliniella tritici (12%). The distribution of thrips within a blueberry planting was investigated using an evenly-spaced grid of white sticky traps in combination with on bush beating-tray samples. Thrips counts from traps correlated with direct counts on the bush across the entire blueberry field (macro-scale level); however, within the field (micro-scale level), there was no correlation between the number of thrips on traps and on individual bushes near traps. Early in the season, trap counts were higher on bushes closer to the forest, indicative of movement of thrips from wild hosts into blueberry fields. However, this was not the case for direct on bush counts or trap counts for the later part of the season, where there was no clear forest “edge” effect. Percent fruit injury due to thrips feeding was low, and it correlated with thrips counts on bushes but not from counts on traps. Overall, our data show that thrips counts on sticky traps need to be interpreted with care because these numbers weakly correlated with the numbers of thrips on bushes at the micro-scale level and percent fruit injury; however, they can be useful predictors of thrips activity across entire blueberry fields (macro-scale).

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.

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.

Thrips see red – flower colour and the host relationships of a polyphagous anthophilic thrips

Abstract 1. The common blossom thrips, Frankliniella schultzei, is a polyphagous anthophilic species that colonises a wide range of host‐plant species across different plant taxa. The environmental cues used by these polyphagous insects to recognise and locate host plants are not known. We therefore determined if colour is an important environmental signal used by F. schultzei to recognise flowers of eight of its more significant host‐plant species.2. The effect of flower colour on the colonisation of different host plant species by F. schultzei was investigated by collecting and analysing the following: (a) numbers of thrips from different heights and aspects of the primary host plant Malvaviscus arboreus, (b) thrips distribution within flowers of Hibiscus rosasinensis, (c) colour reflectance from flowers of eight different host‐plant species, and (d) reflectance from different coloured sticky traps and the number of thrips trapped on them at different times of the day and on different dates.3. The results indicate that: (a) the thrips (both sexes) concentrate towards the top of the primary host plant M. arboreus and are not distributed differentially according to sunny or shady aspect of the plant, (b) the number of female thrips on H. rosasinensis was higher in anthers compared to petals (corolla) and the basal parts of the flower, and males were as numerous on the petals as were females, and (c) there is a common floral reflectance pattern (but with different intensities) across the eight host plant species, mainly in the red part of the spectrum (600–700 nm).4. Results of colour sticky trapping show that red attracts more female thrips compared to any other colour and that most were caught between 09.00 and 11.00 hours. By contrast, more male thrips were trapped between 07.00 and 09.00 hours. Males were more evenly distributed across the different colours but the highest numbers were associated with the yellow traps.5. The higher densities of thrips at the top of their host plant may be related to the early morning (07.00–11.00 hours) activity of the thrips, when the top portions of the plant are more exposed to sunlight. The sex‐related distributions of F. schultzei thrips across time, coloured sticky traps, and various parts of the flowers seem to be related to mating swarm formation by the males, on the one hand, and the relative frequency and intensity of the use of M. arboreus by the females, on the other, as a feeding and oviposition site. Frankliniella schultzei females respond more strongly to red than to any other colours, so it is predicted that the spectral properties of colour recognition by this species will correlate with the predominant red reflectance of its primary host, M. arboreus, and that there may well be a sex‐related difference in colour recognition within this species.

Plant odours with potential for a push–pull strategy to control the onion thrips, Thrips tabaci

AbstractWe compared the efficacy of four plant essential oils to repel onion thrips, Thrips tabaci (Lindeman) (Thysanoptera: Thripidae), in the presence of an attractive odour, ethyl iso‐nicotinate in a pasture field. Four horizontal white sticky plates were placed adjacent to (directions: N, S, E, W) a central horizontal white plate (C). After 24 h, in the treatment combination where the four plates were sprayed with essential oil surrounding a central sticky plate sprayed with ethyl iso‐nicotinate, fewer onion thrips were found on the plates treated with sweet marjoram [Origanum majorana L. (Labiatae)] or clove basil [Ocimum gratissimum L. (Labiatae)] (87 and 71% less, respectively) compared to the control treatment of four water‐sprayed plates surrounding a central plate with ethyl iso‐nicotinate. We also compared the distribution of onion thrips on the plates. Relative thrips numbers on each plate were compared with similar (N, S, E, W, and C) plates in the control treatment. There were relatively lower thrips numbers on the south (23% reduction) and west (26% reduction) O. majorana‐treated plates and higher numbers (37% increase) on the central attractant‐treated plate indicating a short‐distance push–pull effect. When four plates were sprayed with the thrips attractant surrounding a central sticky plate sprayed with an essential oil or water (control), only O. majorana reduced the number of thrips on the attractant‐sprayed plates (62% reduction). The distribution of thrips on the different plates within this treatment combination did not change substantially when compared to the distribution in the water‐control treatment. Other essential oils tested (wormwood [Artemisia arborescens L. (Compositae)]) and tea tree [Melaleuca alternifolia (Maiden. &amp; Betche.) Cheel. (Myrtaceae)]) were not effective in any of the treatments. It appears that O. majorana is a promising thrips repellent which could be used for further testing in a push–pull system with the attractant ethyl iso‐nicotinate. The field setup used also proved to be a valuable tool for evaluating the potential of repellents to control onion thrips.

Within-Plant and Temporal Distribution of Nymphal and Adult Western Flower Thrips,Frankliniella occidentalis(Thysanoptera: Thripidae), on Flowers and Foliage of Greenhouse Impatiens,Impatiens wallerana, and Implications for Pest Population Sampling

The development of cost-effective management and sampling techniques for western flower thrips, Frankliniella occidentalis (Pergande), on garden impatiens, Impatiens wallerana (Hook. f.), requires that information about the within-plant distribution and diurnal patterns of thrips abundance be known. Impatiens flower bud development was divided into five arbitrary stages, representing tightly closed buds through fully opened flowers. Numbers of immature and adult thrips associated with these flower stages were determined at six times daily (0000, 0200, 0600, 0800, 1400, and 2000 hours). In addition, thrips distribution was determined among flowers with and without pollen, and on budless foliage, at two times daily (0800 and 0000 hours). Each successive stage of flower bud development contained significantly more adult female and immature thrips than the previous stage. The oldest flowers contained significantly fewer immature thrips than penultimate stage buds. There was no effect of sampling time on thrips density across flower bud stages. Flowers with pollen had significantly more adult female thrips compared with flowers without pollen, but numbers of adult male and immature thrips were not affected by presence of pollen. Foliage consistently contained the fewest of all life stages of thrips. There was a significant effect of time on female thrips abundance within the fully opened flower with pollen category and no effect of time on immature thrips abundance.