Stuart Reitz

The mRNA Expression Profiles of Five Heat Shock Protein Genes from Frankliniella occidentalis at Different Stages and Their Responses to Temperatures and Insecticides

The western flower thrips, Frankliniella occidentalis(Pergande) is a highly invasive pest that is able to exploit many crops across a wide range of environmental conditions. Five full-length cDNAs of heat shock protein(HSP) genes(Fo-HSP90, Fo-HSP70, Fo-HSP60, Fo-HSP40 and Fo-HSP28.9) were cloned from F. occidentalis, and their expression profiles were investigated under conditions of thermal stress and insecticide exposure, and at different stages during development, using real-time quantitative PCR. All five gene sequences showed high similarity to homologs in other species, indicating the conserved function of this gene family. HSP60 represents an informative phylogenetic marker at the ordinal taxonomic level within Insecta, but HSP90, which has two homologous copies in Hymenoptera, was not informative. T he expression of Fo-HSPs under thermal stress suggests that Fo-HSP90, Fo-HSP70, and Fo-HSP28.9 are inducible by both cold and heat stress, Fo-HSP40 is only heat-inducible, and Fo-HSP60 is thermally insensitive. There were two patterns of cold induction of Fo-HSPs: one is from 0 to 4°C and the other is around-8°C. All five Fo-HSPs genes were induced by exposure to sublethal concentrations of the insecticide avermectin. The expression of the five Fo-HSPs during different developmental stages suggests that they all play a role in development of F. occidentalis.

Field-evolved resistance to insecticides in the invasive western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in China.

BACKGROUND To understand the current status of insecticide resistance of the invasive western flower thrips, Frankliniella occidentalis, in China, the responses of six field populations to six commonly used insecticides, i.e. spinosad, spinetoram, cyantraniliprole, imidacloprid, acetamiprid and pyriproxyfen, were evaluated in comparison with a susceptible laboratory strain. RESULTS Field populations tended to be less susceptible than the laboratory strain. The population from Shouguang, Shandong Province, showed the lowest levels of susceptibility. A 15.64-fold and 17.29-fold resistance to spinosad and spinetoram was detected in the Shouguang population. A 11.74-fold and 13.64-fold resistance to cyantraniliprole was detected in populations from Daxing in the Beijing area and Shouguang. All populations showed a low level of resistance to imidacloprid, acetamiprid and pyriproxyfen, except for the Shouguang population, which was 127.58-fold more resistant to pyriproxyfen. CONCLUSION Variations in resistance to the tested insecticides were observed among the sampled population. Spinosad and spinetoram were the most efficient insecticides and are recommended for use in an integrated management programme. Resistance management strategies should be implemented to reduce the potential for resistance evolving.

Impacts on Natural Enemies and Competitor Thrips of Insecticides against the Western Flower Thrips (Thysanoptera: Thripidae) in Fruiting Vegetables

Abstract Newer, selective insecticides with few negative impacts on natural enemies and competitor species are needed for effective, sustainable management of the western flower thrips, Frankliniella occidentalis (Pergande). The purpose of this study was to evaluate the impacts on natural enemies and competitor thrips species of insecticides used for control of western flower thrips in fruiting vegetables. Trials with tomato (Solanum lycopersicum L.) and with pepper (Capsicum annuum L.) were conducted to evaluate insecticide treatment effects on western flower thrips and natural enemies at the North Florida in 2008, 2009, 2010 and 2011. A number of insecticides from different classes showed moderate to high efficacy against western flower thrips. The broad-spectrum insecticides acetamiprid, methomyl, and tolfenpyrad demonstrated activity against the pest, while also reducing populations of the key predator of thrips in pepper, Orius insidiosus (Say) (Hemiptera: Anthocoridae). Insecticides that showed little impact on populations of O. insidiosus were cyantraniliprole, flonicamid, spirotetramat, and terpenes. Although only moderately active against the western flower thrips, they would be valuable additions to existing management programs for pepper. Insecticides with activity against western flower thrips also showed activity against Frankliniella tritici (Fitch). This non-damaging congener species is a beneficial because it out-competes the western flower thrips, especially in tomato where O. insidiosus is not a major factor in western flower thrips management. Numerous insecticides were identified with activity against the western flower thrips that are suitable for use in integrated pest management programs of fruiting vegetables.

Sublethal Effects of Beauveria bassiana (Ascomycota: Hypocreales) on Life Table Parameters of Frankliniella occidentalis (Thysanoptera: Thripidae).

ABSTRACT We assessed effects of parental exposure to Beauveria bassiana on life history traits of subsequent generations of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Progeny from individuals that survived fungal exposure as second instars had significantly shorter egg stages, but longer prepupal development times than corresponding untreated controls. However, survivorship to adulthood of these progeny groups did not differ. Although fecundities of the parental types did not differ, the sex ratio of progeny from fungal-treated parents was male-biased, whereas sex ratio of progeny from untreated control parents was even.We calculated life table parameters for the progeny and found that all parameters, except for generation time, were significantly less for the progeny of fungal-treated parents than for progeny of untreated parents. The intrinsic rate of increase, finite rate of increase, net reproductive rate, mean generation time, and gross reproductive rate were 0.199 d-1, 1.229 d-1, 21.84, 15.48 d, and 27.273, respectively, for progeny of treated thrips, and 0.266 d-1, 1.316 d-1, 52.540, 14.92 d, and 70.64, respectively, for progeny of control thrips. Consequently, population projections demonstrated that offspring of parents exposed to B. bassiana would increase their population more slowly than those from untreated parents. These results demonstrate that B. bassiana has sublethal effects that reduce the reproductive success of F. occidentalis and these effects should be taken into account when evaluating its use in management programs for F. occidentalis.

Field resistance to spinosad in western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae)

Abstract The western flower thrips, Frankliniella occidentalis, is one of the most destructive sucking pests of vegetables, fruits and ornamental crops in China. Spinosad is one of the most commonly used insecticides to manage thrips. To assess the incidence of spinosad resistance in F. occidentalis field populations in eastern China, survival rates for 24 different populations were compared with those of a susceptible laboratory strain. All populations showed significantly higher resistance to spinosad compared with the control as determined by comparing median lethal concentrations. Two populations from Shouguang and Liaocheng in Shandong Province were classified as having moderate and high levels of resistance to spinosad with a mean resistance ratio of 17.0 and 89.2, respectively. Our research indicates a widespread reduction in spinosad efficacy for controlling F. occidentalis field populations, and that resistance management strategies should be implemented as soon as practicable, to reduce the potential of progressive resistance development and loss of efficacy.

Does temperature-mediated reproductive success drive the direction of species displacement in two invasive species of leafminer fly?

Liriomyza sativae and L. trifolii (Diptera: Agromyzidae) are two highly invasive species of leafmining flies, which have become established as pests of horticultural crops throughout the world. In certain regions where both species have been introduced, L. sativae has displaced L. trifolii, whereas the opposite has occurred in other regions. These opposing outcomes suggest that neither species is an inherently superior competitor. The regions where these displacements have been observed (southern China, Japan and western USA) are climatically different. We determined whether temperature differentially affects the reproductive success of these species and therefore if climatic differences could affect the outcome of interspecific interactions where these species are sympatric. The results of life table parameters indicate that both species can develop successfully at all tested temperatures (20, 25, 31, 33°C). L. sativae had consistently higher fecundities at all temperatures, but L. trifolii developed to reproductive age faster. Age-stage specific survival rates were higher for L. sativae at low temperatures, but these were higher for L. trifolii at higher temperatures. We then compared the net reproductive rates (R 0) for both species in pure and mixed cultures maintained at the same four constant temperatures. Both species had significantly lower net reproductive rates in mixed species cultures compared with their respective pure species cultures, indicating that both species are subject to intense interspecific competition. Net reproductive rates were significantly greater for L. sativae than for L. trifolii in mixed species groups at the lower temperatures, whereas the opposite occurred at the higher temperature. Therefore, interactions between the species are temperature dependent and small differences could shift the competitive balance between the species. These temperature mediated effects may contribute to the current ongoing displacement of L. sativae by the more recent invader L. trifolii in warm climatic areas of China.

Production of microsclerotia of the fungal entomopathogen Lecanicillium lecanii (Hypocreales: Cordycipitaceae) as a biological control agent against soil-dwelling stages of Frankliniella occidentalis (Thysanoptera: Thripidae)

Abstract Microsclerotia (MS) production by two isolates of Lecanicillium lecanii on various culture media is described, and the efficacy of MS against western flower thrips is evaluated. High concentrations of MS (2.9–3.1×105·mL−1) were produced in media with C:N ratios of 7.4:1 and 10.3:1 by isolate SN21. Bioassays using soil-incorporated MS resulted in significant infection and mortality of thrips.

A decade of leafminer invasion in China: lessons learned

Liriomyza trifolii (Burgess) is a highly invasive species that has become established in agricultural and ornamental crops throughout the world. L. trifolii was first recorded in China in 2005 in Guangdong Province. Subsequently, its known distribution in China has rapidly expanded to another 11 provinces (Zhejiang, Jiangsu, Shanghai, Fujian, Guangxi, Shandong, Hainan, Hebei, Henan, Hubei and Anhui), where it is currently causing considerable damage and economic losses. Experimental research and field surveys have contributed to our understanding of the ecology of L. trifolii and particularly the process of invasion and its interactions with other established, exotic Liriomyza leafminer species. A number of factors have contributed to the successful establishment of L. trifolii and displacement of interspecific competitors. In China, L. trifolii has become a particularly devastating pest in areas with intensive farming with extensive monocultures and a reliance on insecticide use. Integrated pest management incorporating judicious applications of insecticide combined with biological and cultural controls is likely to provide the best long-term management strategy for L. trifolii. We provide information regarding 10 years of L. trifolii invasion in China and discuss areas of future research to enhance our overall understanding of the biology and ecology of L. trifolii and to improve management programmes for this widespread invasive insect pest.

Molecular Survey for the Invasive Leafminer Pest Liriomyza huidobrensis (Diptera: Agromyzidae) in California Uncovers Only the Native Pest Liriomyza langei

ABSTRACT Liriomyza huidobrensis (Blanchard) is a highly destructive invasive leafminer pest currently causing extensive damage to vegetable and horticultural crops around the world. Liriomyza langei Frick is a leafminer pest native to California that cannot currently be morphologically distinguished from L. huidobrensis. We used a DNA-barcoding approach, a published PCR-RFLP method, and a new multiplex PCR method to analyze 664 flies matching the morphological description of huidobrensis—langei. We found no evidence for the presence of L. huidobrensis in our extensive samples from California. In addition to the new molecular method, this work is important because it provides definitive data that the California “pea leafminer” is currently, and has probably always been, L. langei. These data will also be important in the event that the highly invasive L. huidobrensis ever becomes established.

Onion Thrips (Thysanoptera: Thripidae) and Their Management in the Treasure Valley of the Pacific Northwest

Abstract Onion thrips, Thrips tabaci Lindeman and thrips-transmitted Iris yellow spot virus are the most significant pest complex affecting onion production in the Treasure Valley of eastern Oregon and southwestern Idaho. Thrips feeding damage and virus infection significantly reduce onion bulb size and economic returns for this high value crop. The high concentration of onion fields in the Treasure Valley and the long, hot, dry growing season present a number of challenges for managing onion thrips and Iris yellow spot virus (IYSV). Insecticides are the primary tool that growers have to manage this pest complex. With the long growing season, growers need to exercise good insecticide resistance management programs to maintain the effectiveness of currently available insecticides. To do this, growers need to rotate among available products and use as few applications as practical. A challenge for researchers is to determine not only which insecticides are effective but also to determine when during the season different products may be most effectively used. Techniques for analyzing field trial data are discussed, including comparing changes in pest populations before and after various insecticide applications are made. These comparisons can be made through the use of linear estimates and contrasts as part of analyses of variance, and they can aid in determining efficacy of different treatments by accounting for pre-application populations. These techniques will help researchers in developing sound sequence of insecticide applications for onion thrips management.