Resistance to Thrips palmi (Thysanoptera: Thripidae) in beans

Resistance in beans, Phaseolus vulgaris L., to the melon thrips Thrips palmi Karny was studied under field conditions at two sites in Colombia. Genotypes were rated for resistance on the basis of visual damage scores, bean production ratings (a visual estimate of pod and seed set), and grain yields. Of 1,138 genotypes tested, only 60 (5.3%) were rated as resistant. Repeated testing allowed us to identify potential sources of resistance in five germplasm accessions (G 02402, G 02852, G 03177, G 03569, and G 04055), one commercial variety ('Brunca'), six elite breeding lines (A 216, DOR 714, EMP 486, FEB 115, FEB 161, and FEB 162), 41 recombinant inbred lines derived from the BAT 881 x G 21212 cross, and seven recombinant inbred lines derived from a cross between DOR 364 and BAT 477. Resistance was not associated with maturity, growth habit, pubescence, and seed color or seed size. In general, correlations between visual damage scores and bean production ratings and between damage scores and yield were high and significant meaning that selection on damage rating is useful to identify genotypes that may have tolerance as a mechanism of resistance. The continuous distribution of damage scores of 139 recombinant inbred lines suggested that the inheritance of resistance to the melon thrips might be quantitative. Overall, resistance levels in beans can be considered as moderate, because none of the genotypes tested received damage scores of <3 on a 1-9 scale and none was ever rated as highly resistant in terms of bean production ratings.     

Soil application of Beauveria bassiana JEF-350 granules to control melon thrips,thrips palmi Karny (Thysanoptera: Thripidae)

The melon thrip, Thrips palmi Karny, is a worldwide pest that causes severe damage to a wide range of host plants. Current management mainly relies on sprayable synthetic chemicals that target adult, egg, and larval stages. However, these chemicals have adverse effects on the environment and induce resistance in thrips. An alternative environmentally sound management method with a different mode of action, targeting the soil-dwelling stage of thrips, was considered in this work. Bioassay of seven Beauveria bassiana isolates under laboratory conditions revealed that two isolates, JEF-350 and JEF-341, were highly virulent against melon thrips. Conidial production and thermotolerance of JEF-341 and JEF-350 were compared with those of the commercial isolate B. bassiana ERL836 (Chongchaesak GR). B. bassiana JEF-350 showed similar conidial production to ERL836 but had significantly higher thermotolerance than JEF-341 and ERL836. Dose-dependent virulence of JEF-350 was tested in pot and field conditions, and JEF-350 millet-based fungal granules were applied to the soil surface to target the pupal stage of melon thrips. In the pot and field trials, JEF-350 granules significantly reduced thrip population with greater efficacy than JEF-341 and ERL836 granules. In application, JEF-350 needs to be carefully applied when in combination with chemical fungicides to ensure survival. Our results suggest that B. bassiana JEF-350 could be effectively used to control the pupal stage of melon thrips in soil.     

Development of a sequence-specific real-time PCR to the melon thrips Thrips palmi (Thysan., Thripidae)

Abstract:  In recent years, the polyphagous pest Thrips palmi Karny has become a species of major quarantine concern, often intercepted on plant material in international trade. The ability to rapidly identify the species is a critical factor that will determine the success of any campaign to prevent its establishment in Europe or elsewhere. However, the immature stages cannot currently be identified to the species level with certainty by morphological methods. In this study, random amplified polymorphic DNA analysis was performed to identify putative markers, which were then screened by Southern blot analysis. One marker was sequenced and a real-time polymerase chain reaction assay developed. The assay was screened against 21 thrips species including 10 other species of the genus Thrips and were found to be specific to T. palmi . The assay is rapid, could be completed in as little as 45 min and can be used to aid the identification of T. palmi .     

Transmission of capsicum chlorosis virus by Thrips palmi (Thysanoptera: Thripidae)

Applied Entomology and Zoology - Transmission efficiencies of capsicum chlorosis virus (CaCV) were investigated for four thrips species (Thysanoptera: Thripidae), Frankliniella occidentalis...     

Antixenosis and antibiosis of common beans to Thrips palmi Karny (Thysanoptera: Thripidae)

Antixenosis and antibiosis in the resistance of common beans (Phaseolus vulgaris L.) to the melon thrips, Thrips palmi Karny, were investigated under laboratory and field conditions. Experiments were conducted for four moderately resistant genotypes ('Brunca', BH-130, EMP 486, and FEB 115) in comparison with one susceptible genotype (APN 18). Multiple-choice tests recorded most thrips on EMP 486 and least on FEB 115. Dual-choice tests conducted in both laboratory and field confirmed the antixenotic effect of FEB 115 and the attractant effect of EMP 486 on thrips. These results demonstrate the significance of antixenosis in the resistance of common beans to T. palmi. Life-table studies showed significant differences in egg duration, immature and adult survivorship, female body length and longevity, daily oviposition rate, and total fecundity among the bean genotypes. The intrinsic rate of natural increase (r(m)) and its associated population parameters varied significantly with the bean genotype on which T. palmi cohorts were reared. Based on mean r(m) values, the five bean genotypes can be divided into two groups, with BH-130 and 'Brunca' being less favorable for the population growth of thrips than EMP 486 and FEB 115; the latter were comparable to the susceptible genotype APN 18. These life-table results indicate the role of antibiosis in enhancing the resistance of common beans to T. palmi.     

Molecular differences in the mitochondrial cytochrome oxidase I (mtCOI) gene and development of a species-specific marker for onion thrips, Thrips tabaci Lindeman, and melon thrips, T. palmi Karny (Thysanoptera: Thripidae), vectors of tospoviruses (Bunyaviridae)

A quick and developmental-stage non-limiting method of the identification of vectors of tospoviruses, such as Thrips tabaci and T. palmi, is important in the study of vector transmission, insecticide resistance, biological control, etc. Morphological identification of these thrips vectors is often a stumbling block in the absence of a specialist and limited by polymorphism, sex, stage of development, etc. Molecular identification, on the other hand, is not hampered by the above factors and can easily be followed by a non-specialist with a little training. The mitochondrial cytochrome oxidase I (mtCOI) exhibits reliable inter-species variations as compared to the other markers. In this communication, we present the differences in the mtCOI partial sequence of morphologically identified specimens of T. tabaci and T. palmi collected from onion and watermelon, respectively. Species-specific markers, identified in this study, could successfully determine T. tabaci and T. palmi, which corroborated the morphological identification. Phylogenetic analyses showed that both T. tabaci and T. palmi formed different clades as compared to the other NCBI accessions. The implication of these variations in vector efficiency has to be investigated further. The result of this investigation is useful in the quick identification of T. tabaci and T. palmi, a critical factor in understanding the epidemiology of the tospoviruses, their management and also in quarantine.     

Colour preference and potato cultivar oviposition choice by onion thrips,Thrips tabaci (Thysanoptera: Thripidae)

Thrips tabaci (Lindeman) is an important polyphagous pest, and vector of Tomato spotted wilt virus responsible for sporadic, but devastating epidemics in potato. T. tabaci shows significant preferential differences between potato cultivars that may be important for field resistance. To investigate the role of visual cues in host choice we tested colour preference using two-choice assays. Thrips tabaci showed a significant preference for mid-green over red, blue, and white coloured cards, a preference for both light-green and mid-green over dark-green, and light-green over yellow, but no preferential difference between mid-green and yellow, and between light-green and mid-green. Analysis of the spectral reflectance of potato cultivars differing in thrips preference, revealed significant differences within the 400–700 nm wavelengths. In most cases cultivars preferred by T. tabaci had lighter green foliage and higher reflectance at 552 nm, and thus colour preference may be important for host selection. Oviposition choice of T. tabaci for potato cultivars was determined from counts of larvae and unhatched eggs from leaf disks under choice and no-choice conditions. In contrast to the colour choice experiments, onion thrips showed oviposition preference for cultivars with darker green foliage and lower reflectance at 552 nm.     

Potential for the use of biological agents for the control of Thrips palmi (Thysanoptera: Thripidae) outbreaks

Thrips palmi is a major pest of many crops in the tropics and sub-tropics, and is a serious threat within the protected horticulture industry in other parts of the world including the UK. Widespread use of insecticides against T. palmi throughout the world coupled with the restricted range of products available makes it essential to find alternative systems for control. The scattered information on its natural enemies, particularly predators and parasitoids, is reviewed and their potential for use in the control of T. palmi as part of IPM strategies in the UK is considered. Natural enemies selected for detailed examination include: Amblyseius spp., Anthocoris nemoralis, Atheta coriaria, Bilia spp., Campylomma spp., Ceranisus spp., Deraeocoris spp., Franklinothrips spp., Hypoaspis spp., Orius spp. and Phytoseius spp. Recommendations for further investigations are made, including screening and efficacy testing of candidate predators and parasitoids, using semiochemicals to enhance their effectiveness, and assessing the compatibility of chosen species with other components of an IPM system.     

An observation on the embryonic development in Thrips palmi (Thysanoptera: Thripidae) eggs obtained by an artificial oviposition setup

Thrips palmi is an important insect pest of vegetables and ornamental crops worldwide. Besides direct damage caused by feeding, it transmits several tospoviruses in a persistent-propagative manner. Eggs of T. palmi are microscopic and embedded within plant tissue by the sharp ovipositor of adult female. In the present study, an artificial oviposition setup has been standardized for T. palmi. Eggs of T. palmi were harvested in sterile water between two thin membranes. The developmental stages of T. palmi embryo were studied starting from oviposition up to hatching by inverted and confocal reflection microscopy. Energids were homogeneously distributed at an early stage of development. The anterior end of the egg curved with a constriction post 38 h. Initiation of tissue organization, mouthparts, appendages, compound eyes were observed at different time points. Appendages were well developed and segmentation was prominent post 70 h. The embryo was completely developed at around 80 h and hatched by 86 h post oviposition at 28 °C temperature. The study first time reports the embryonic development of T. palmi that would be helpful in detailed investigations of thrips developmental biology and evolution.     

Fumigant toxicity of plant essential oils to Thrips palmi (Thysanoptera: Thripidae) and Orius strigicollis (Heteroptera: Anthocoridae)

The fumigant toxicity of 92 plant essential oils to adult Thrips palmi Karny (Thysanoptera: Thripidae) and Orius strigicollis Poppius (Heteroptera: Anthocoridae) was examined by using a vapor phase toxicity bioassay and compared with those of dichlorvos, emamectin benzoate, spinosad, and thiamethoxam, four commonly used insecticides. Responses varied according to oil type and insect species. As judged by 24-h LC50 values, pennyroyal oil (2.63 mg/liter air) was the most toxic fumigant and was 23.6-fold more toxic than dichlorvos (62.09 mg/liter air) against adult T. palmi. Potent fumigant toxicity (LC50, 11.03-19.21 mg/liter air) was observed in armoise, basil, cedarleaf, coriander, cypress, howood, hyssop, marjoram, myrtle, niaouli, rosemary, and sage (Dalmatia) oils. Neither emamectin benzoate, spinosad, nor thiamethoxam exhibited fumigant action. Against adult O. strigicollis, dichlorvos (LC50, 6.3 x 10(-6) mg/liter air) was the most toxic fumigant, whereas the LC50 values of the 13 essential oils ranged from 17.29 to 158.22 mg/liter air. O. strigicollis was 1.4-22.1 times less susceptible than T. palmi to the essential oils. The essential oils described merit further study as potential fumigants for the control of T. palmi in greenhouses.     

Regional and temporal variation in susceptibility to lambda-cyhalothrin in onion thrips, Thrips tabaci (Thysanoptera: Thripidae), in onion fields in New York

Populations of onion thrips, Thrips tabaci Lindeman, from commercial onion fields in New York were evaluated for their susceptibility to the commonly used pyrethroid, lambda-cyhalothrin (Warrior T), using a novel system called the Thrips Insecticide Bioassay System (TIBS). To use TIBS, thrips are collected directly from the plant into an insecticide-treated 0.5-ml microcentrifuge tube that has a flexible plastic cap with a small well into which 0.08 ml of a 10% sugar-water solution with food colorant is deposited. The solution is sealed into the well with a small piece of stretched parafilm through which the thrips can feed on the solution. Thrips mortality is assessed after 24 h with the help of a dissecting stereoscope. In 2001, onion thrips populations were collected from 16 different sites and resistance ratios were >1,000 in five populations. Percent mortality at 100 ppm, a recommended field rate, varied from 9 to 100%, indicating high levels of variation in susceptibility. Particular instances of resistance appeared to be the result of practices within an individual field rather than a regional phenomenon. In 2002, we also observed large differences in onion thrips susceptibility, not only between individual fields but also between thrips collected in a single field at mid season and late season, again suggesting that insecticide-use practices within an individual field caused differences in susceptibility. Additional tests indicated no differences in susceptibility between adult and larval onion thrips populations and only relatively minor differences between populations collected from different parts of the same field. Using TIBS, several populations of onion thrips with different susceptibilities to lambda-cyhalothrin were identified and then subjected to lambda-cyhalothrin-treated onion plants. There was a highly significant positive relationship between percent mortality of thrips from TIBS and percent mortality from the treated onion plants, indicating that results from TIBS could be used to predict spray performance. These data suggest that use of TIBS for evaluating susceptibility to particular insecticides could be instrumental for developing a resistance management strategy for onion thrips.     

High nucleotide diversity in the para-like voltage-sensitive sodium channel gene sequence in the western flower thrips (Thysanoptera: Thripidae)

In a search for a pyrethroid resistance diagnostic marker, a partial sequence of the para-like sodium channel gene was obtained from 78 diploid females of the arrhenotokous insect pest species Frankliniella occidentalis (Pergande), the western flower thrips. Although all the insects analyzed came from a single laboratory population, nine different haplotypes were obtained. Two haplotypes did have the well-known L to F kdr mutation, but only one of these could be statistically linked to pyrethroid resistance in our population. This haplotype did not have the superkdr mutation, but did have a unique mutation a few amino acids downstream, at a position already linked to resistance in Plutella. Although this para-like locus seemed to have a role in pyrethroid resistance in our population, other resistance mechanisms were also probably involved. The fact that our laboratory population, open to migration, contained ahigh genetic diversity forthis selected gene shows that "pest tourism" is a major factor for resistance dynamics in this greenhouse pest. This, with the possible occurrence of an original resistance mutation, might preclude the use of very specific approaches for resistance monitoring in the field in this species.     

Biotic resistance limits the invasiveness of the western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae), in Florida

The spread of the western flower thrips, Frankliniella occidentalis (Pergande), has resulted in the world‐wide destabilization of established integrated pest management programs for many crops. It is hypothesized that frequent exposure to insecticides in intensive agriculture selected for resistant populations, which allowed invasive populations in the eastern USA to overcome biotic resistance from the native community of species. Research conducted in Florida to understand the role of biotic factors in limiting the abundance of the western flower thrips is reviewed. Orius spp. (Hemiptera: Anthocoridae) are effective predators that suppress populations of thrips on crop and non‐crop hosts in southern and northern Florida. Orius are more effective predators of the western flower thrips than the native flower thrips, F. tritici (Fitch) and F. bispinosa (Morgan). The native species are competitors of the western flower thrips. Excessive fertilization and the use of broad‐spectrum insecticides in crop fields further enhances populations of the western flower thrips. Interactions with native species clearly limit the abundance of western flower thrips in Florida, but populations are abundant in fertilized crop fields where application of insecticides excludes predators and competitor species.     

Effect of temperature and host plant leaf morphology on the efficacy of two entomopathogenic biocontrol agents of Thrips palmi (Thysanoptera: Thripidae)

The efficacy of two entomopathogenic biocontrol agents, Steinernema feltiae (Filipjev) and Verticillium lecanii (Zimmerman) Viégas (reclassified now as Lecanicillium muscarium (Petch) Zare & Gams), against Thrips palmi Karny was investigated. Assessments of the effect of temperature on the efficacy of S. feltiae indicated that higher mortality of T. palmi was recorded at 20 degrees C compared to either 15 or 25 degrees C, whereas significantly higher T. palmi mortality followed application of L. muscarium at 25 degrees C. Testing the control agents efficacy on three host plants; chrysanthemum, sweet pepper and cucumber, under constant temperature and high humidity conditions produced no significant difference in the level of T. palmi larval mortality on each host plant. Incorporating the chemical insecticide imidacloprid with both biological agents in a combined control strategy increased T. palmi juvenile mortality. The potential role of S. feltiae and L. muscarium within integrated pest management programmes for the control of T. palmi is discussed.     

Temperature and precipitation affect seasonal patterns of dispersing tobacco thrips, Frankliniella fusca, and onion thrips, Thrips tabaci (Thysanoptera: Thripidae) caught on sticky traps

Effects of temperature and precipitation on the temporal patterns of dispersing tobacco thrips, Frankliniella fusca, and onion thrips, Thrips tabaci, caught on yellow sticky traps were estimated in central and eastern North Carolina and eastern Virginia from 1997 through 2001. The impact that these environmental factors had on numbers of F. fusca and T. tabaci caught on sticky traps during April and May was determined using stepwise regression analysis of 43 and 38 site-years of aerial trapping data from 21 and 18 different field locations, respectively. The independent variables used in the regression models included degree-days, total precipitation, and the number of days in which precipitation occurred during January through May. Each variable was significant in explaining variation for both thrips species and, in all models, degree-days was the single best explanatory variable. Precipitation had a comparatively greater effect on T. tabaci than F. fusca. The numbers of F. fusca and T. tabaci captured in flight were positively related to degree-days and the number of days with precipitation but negatively related to total precipitation. Combined in a single model, degree-days, total precipitation, and the number of days with precipitation explained 70 and 55% of the total variation in the number of F. fusca captured from 1 April through 10 May and from 1 April through 31 May, respectively. Regarding T. tabaci flights, degree-days, total precipitation, and the number of days with precipitation collectively explained 57 and 63% of the total variation in the number captured from 1 April through 10 May and from 1 April through 31 May, respectively.     

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.