Effects of cis-Jasmone Treatment of Brassicas on Interactions With Myzus persicae Aphids and Their Parasitoid Diaeretiella rapae.

There is a need to develop new ways of protecting plants against aphid attack. Here, we investigated the effect of a plant defence activator, cis-jasmone (CJ), in a range of cultivars of Brassica napus, Brassica rapa and Brassica oleracea. Plants were sprayed with cis-jasmone or blank formulation and then tested with peach potato aphids (Myzus persicae Sulzer) (Hemiptera: Aphididae) and their parasitoid Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae). CJ treated plants had significantly lower aphid settlement than control plants in a settlement bioassay. Conversely, in a foraging bioassay, D. rapae parasitoids spent a significantly longer time foraging on CJ treated plants. Our results reveal that CJ treatment makes plants less attractive to and less suitable for M. persicae but more attractive to D. rapae in a range of brassica cultivars. It is likely that these effects are due to changes in volatile emission indicating activation of defence and presence of conspecific competitors to aphids but presence of prey to parasitoids. Increases in volatile emission were found in CJ induced plants but varied with genotype. Among the synthetic volatile compounds that were induced in the headspace of CJ treated brassica cultivars, methyl isothiocyanate, methyl salicylate and cis-jasmone were most repellent to aphids. These results build on earlier studies in Arabidopsis and show that tritrophic interactions are influenced by CJ in a wide range of brassica germplasm. The implication is that CJ is a promising treatment that could be used in brassica crops as part of an integrated pest management system.

Mating behaviour, mate choice and female resistance in the bean flower thrips (Megalurothrips sjostedti).

Many species of thrips (Thysanoptera) in the family Thripidae form mating aggregations, but the adaptive significance of these aggregations and the extent of male and female mate choice is poorly understood. We studied the mating behaviour of the bean flower thrips Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), which forms male aggregations and occurs across sub-Saharan Africa. We tested whether males choose mates by female age or mating status. No-choice mating bioassays with one male and one female were used to simulate the way males usually encounter only one female at a time in aggregations in the field. Virgin females violently resisted mating attempts by males, but we found no compelling evidence to establish whether this was indiscriminate or was screening suitable males. Younger males (1-2 days old) did not discriminate females by age (1-2 or 7-10 days old), but older males (7-10 days old) avoided mating with older females. Any male choice by female mating status (virgin or mated) was weak or absent. The mating behaviour of M. sjostedti shows broad similarities with that of other thrips species that form aggregations, but also shows some distinct and novel differences, which can help our understanding of the adaptive significance of aggregations.

Semiochemicals for Thrips and Their Use in Pest Management.

Thrips (Thysanoptera) are small insects that can cause huge problems in agriculture, horticulture, and forestry through feeding and the transmission of plant viruses. They produce a rich chemical diversity of pheromones and allomones and also respond to a broad range of semiochemicals from plants. These semiochemicals offer many opportunities to develop new approaches to pest management. Aggregation pheromones and plant-derived semiochemicals are already available in commercial products. We review these semiochemicals and consider how we can move away from using them mainly for monitoring to using them for control. We still know very little about the behavioral responses of thrips to semiochemicals, and we show that research in this area is needed to improve the use of semiochemicals in pest management. We also propose that thrips should be used as a model system for semiochemically mediated behaviors of small insects that have limited ability to fly upwind.

Invasion Biology, Ecology, and Management of Western Flower Thrips.

Western flower thrips, Frankliniella occidentalis, first arose as an important invasive pest of many crops during the 1970s-1980s. The tremendous growth in international agricultural trade that developed then fostered the invasiveness of western flower thrips. We examine current knowledge regarding the biology of western flower thrips, with an emphasis on characteristics that contribute to its invasiveness and pest status. Efforts to control this pest and the tospoviruses that it vectors with intensive insecticide applications have been unsuccessful and have created significant problems because of the development of resistance to numerous insecticides and associated outbreaks of secondary pests. We synthesize information on effective integrated management approaches for western flower thrips that have developed through research on its biology, behavior, and ecology. We further highlight emerging topics regarding the species status of western flower thrips, as well as its genetics, biology, and ecology that facilitate its use as a model study organism and will guide development of appropriate management practices.

Experienced males recognise and avoid mating with non-virgin females in the western flower thrips.

The western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) is a major insect pest on a wide range of crops throughout the world. There are several unexplained aspects of the mating behaviour, particularly in relation to male-male competition and mate choice. The objectives of the study were to test whether males can detect the mating status of females and whether males avoid mating with previously mated females. Experiments involved either 'experienced' adults taken from a laboratory culture, which had been exposed to high densities of thrips, or virgin adults reared individually. Experienced males mated readily with virgin females, but avoided mating with experienced females. Virgin males showed much less discrimination between females. Avoidance of mating with experienced females is likely to be widespread because it occurred in populations from both the United Kingdom and Kenya. Experienced males also mated with dead virgin females, but avoided mating with dead experienced females, which ruled out the possibility that behavioural differences between the females were responsible. To test whether males could detect whether or not females had mated, virgin females of the same age from the same cohort were either mated once or not mated. Experienced males mated with the dead females that were virgin and avoided mating with the dead females that differed only in that they had mated once shortly before. This showed that males recognise whether or not a female has mated and avoid mating with previously mated females. This avoidance by males suggests that mated females are not usually subjected to high levels of male harassment. The most likely explanation of the avoidance is that males produce an antiaphrodisiac pheromone that is applied to females during mating.

Characterization of Male-Produced Aggregation Pheromone of the Bean Flower Thrips Megalurothrips sjostedti (Thysanoptera: Thripidae).

Aggregation of the bean flower thrips, Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), has been observed on cowpea, Vigna unguiculata (L.) Walp. To understand the mechanism underpinning this behavior, we studied the responses of M. sjostedti to headspace volatiles from conspecifics in a four-arm olfactometer. Both male and female M. sjostedti were attracted to male, but not to female odor. Gas chromatography/mass spectrometry (GC/MS) analyses revealed the presence of two distinct compounds in male M. sjostedti headspace, namely (R)-lavandulyl 3-methylbutanoate (major compound) and (R)-lavandulol (minor compound); by contrast, both compounds were only present in trace amounts in female headspace collections. A behavioral assay using synthetic compounds showed that male M. sjostedti was attracted to both (R)-lavandulyl 3-methylbutanoate and (R)-lavandulol, while females responded only to (R)-lavandulyl 3-methylbutanoate. This is the first report of a male-produced aggregation pheromone in the genus Megalurothrips. The bean flower thrips is the primary pest of cowpea, which is widely grown in sub-Saharan Africa. The attraction of male and female M. sjostedti to these compounds offers an opportunity to develop ecologically sustainable management methods for M. sjostedti in Africa.

Reduced translucency and the addition of black patterns increase the catch of the greenhouse whitefly, Trialeurodes vaporariorum, on yellow sticky traps.

The greenhouse whitefly Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) is a pest of a wide range of vegetable and ornamental crops in greenhouses around the world. Yellow sticky traps are highly attractive to flying adults and so are frequently used to monitor the pest. Our aim was to test whether changes in trap translucency or the addition of printed black patterns could increase the catch on yellow sticky traps in greenhouses. Field trials were carried out in commercial crops of strawberry and tomato under glass over three years. Reduced trap translucency increased trap catches by a factor of 1.5 to 7.0 and the catch increased significantly for both females and males. Spectrometer measurements showed that the increased catch was consistent with an increased landing stimulus from a colour opponency mechanism i.e. the ratio of energy from 500-640 nm to the energy from 300-500 nm. Printed black patterns increased trap catches on specific types of trap, by a factor of 1.4 to 2.3, and the catch increased significantly for both females and males. The patterns increased trap catch on moderately translucent traps, but decreased trap catch on less translucent traps. The evidence points to a contrast/edge effect of pattern, but laboratory experiments are needed to clarify this. Exploitation of these translucency and pattern effects could improve the efficacy of yellow traps for monitoring and mass trapping in crops.

Predatory mites double the economic injury level of Frankliniella occidentalis in strawberry.

The western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) causes bronzing to strawberry fruit. Management of insecticide-resistant strains relies on the integration of predators with carefully timed use of the few insecticides available. Effective management requires better understanding of economic injury levels (EILs) and the factors that affect them. The densities of F. occidentalis and the predatory mite Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae) were manipulated in field experiments. All stages of flower and fruit were susceptible to thrips damage, but larvae caused nearly twice as much damage as adults per individual. The EIL was about four adult thrips per flower in the absence of predators, but increased to over eight at densities of N. cucumeris typical of good establishment in crops. The EIL could be increased by about 0.7 adult thrips per flower for every N. cucumeris per flower. The results were supported by measurements of EILs in commercial crops.

Draft Genomes, Phylogenetic Reconstruction, and Comparative Genomics of Two Novel Cohabiting Bacterial Symbionts Isolated from Frankliniella occidentalis.

Obligate bacterial symbionts are widespread in many invertebrates, where they are often confined to specialized host cells and are transmitted directly from mother to progeny. Increasing numbers of these bacteria are being characterized but questions remain about their population structure and evolution. Here we take a comparative genomics approach to investigate two prominent bacterial symbionts (BFo1 and BFo2) isolated from geographically separated populations of western flower thrips, Frankliniella occidentalis. Our multifaceted approach to classifying these symbionts includes concatenated multilocus sequence analysis (MLSA) phylogenies, ribosomal multilocus sequence typing (rMLST), construction of whole-genome phylogenies, and in-depth genomic comparisons. We showed that the BFo1 genome clusters more closely to species in the genus Erwinia, and is a putative close relative to Erwinia aphidicola. BFo1 is also likely to have shared a common ancestor with Erwinia pyrifoliae/Erwinia amylovora and the nonpathogenic Erwinia tasmaniensis and genetic traits similar to Erwinia billingiae. The BFo1 genome contained virulence factors found in the genus Erwinia but represented a divergent lineage. In contrast, we showed that BFo2 belongs within the Enterobacteriales but does not group closely with any currently known bacterial species. Concatenated MLSA phylogenies indicate that it may have shared a common ancestor to the Erwinia and Pantoea genera, and based on the clustering of rMLST genes, it was most closely related to Pantoea ananatis but represented a divergent lineage. We reconstructed a core genome of a putative common ancestor of Erwinia and Pantoea and compared this with the genomes of BFo bacteria. BFo2 possessed none of the virulence determinants that were omnipresent in the Erwinia and Pantoea genera. Taken together, these data are consistent with BFo2 representing a highly novel species that maybe related to known Pantoea.

Identification of the aggregation pheromone of the melon thrips, Thrips palmi.

The objective of this study was to identify the aggregation pheromone of the melon thrips Thrips palmi, a major pest of vegetable and ornamental plants around the world. The species causes damage both through feeding activities and as a vector of tospoviruses, and is a threat to world trade and European horticulture. Improved methods of detecting and controlling this species are needed and the identification of an aggregation pheromone will contribute to this requirement. Bioassays with a Y-tube olfactometer showed that virgin female T. palmi were attracted to the odour of live males, but not to that of live females, and that mixed-age adults of both sexes were attracted to the odour of live males, indicating the presence of a male-produced aggregation pheromone. Examination of the headspace volatiles of adult male T. palmi revealed only one compound that was not found in adult females. It was identified by comparison of its mass spectrum and chromatographic details with those of similar compounds. This compound had a structure like that of the previously identified male-produced aggregation pheromone of the western flower thrips Frankliniella occidentalis. The compound was synthesised and tested in eggplant crops infested with T. palmi in Japan. Significantly greater numbers of both males and females were attracted to traps baited with the putative aggregation pheromone compared to unbaited traps. The aggregation pheromone of T. palmi is thus identified as (R)-lavandulyl 3-methyl-3-butenoate by spectroscopic, chromatographic and behavioural analysis.

Can mass trapping reduce thrips damage and is it economically viable? Management of the Western flower thrips in strawberry.

The western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is a cosmopolitan, polyphagous insect pest that causes bronzing to fruit of strawberry (Fragaria x ananassa). The main aim of this study was to test whether mass trapping could reduce damage and to predict whether this approach would be economically viable. In semi-protected strawberry crops, mass trapping of F. occidentalis using blue sticky roller traps reduced adult thrips numbers per flower by 61% and fruit bronzing by 55%. The addition of the F. occidentalis aggregation pheromone, neryl (S)-2-methylbutanoate, to the traps doubled the trap catch, reduced adult thrips numbers per flower by 73% and fruit bronzing by 68%. The factors affecting trapping efficiency through the season are discussed. Damage that would result in downgrading of fruit to a cheaper price occurred when bronzing affected about 10% of the red fruit surface. Cost-benefit analysis using this threshold showed that mass trapping of thrips using blue sticky roller traps can be cost-effective in high-value crops. The addition of blue sticky roller traps to an integrated pest management programme maintained thrips numbers below the damage threshold and increased grower returns by a conservative estimate of £2.2k per hectare. Further work is required to develop the F. occidentalis aggregation pheromone for mass trapping and to determine the best timing for trap deployment. Mass trapping of thrips is likely to be cost-effective in other countries and other high-value crops affected by F. occidentalis damage, such as cucumber and cut flowers.

A male-predominant cuticular hydrocarbon, 7-methyltricosane, is used as a contact pheromone in the western flower thrips Frankliniella occidentalis.

In a laboratory bioassay, adult female Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) spent more time near filter paper disks that had been exposed to adult males than near unexposed disks; this effect was not observed on disks exposed to adult females. The response could only partly be explained by the known male-produced aggregation pheromone, neryl (S)-2-methylbutanoate, suggesting the presence of an unknown male-produced compound. In gas chromatography/mass spectrometry analyses, 7-methyltricosane was detected on disks exposed to males, but not on disks exposed to females. Extracts of cuticular lipids also showed relatively large amounts of 7-methyltricosane on males, whereas only trace amounts were found on females and none on larvae. Bioassays of synthetic 7-methyltricosane showed that adults responded only after contact. The response to this compound was clearly different from that to n-tricosane or hexane-only controls. Females that contacted 7-methyltricosane on glass beads stayed in the vicinity and frequently raised the abdomen, a behavior that rejects mating attempts by males. Males stayed in the vicinity and wagged the abdomen sideways, a behavior used in fighting between males. This is the first identification of a contact pheromone in the order Thysanoptera.

Identification of a male-produced aggregation pheromone in the western flower thrips Frankliniella occidentalis.

Two major components have been detected in the headspace volatiles of adult male Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) that are not present in the headspace volatiles of adult females. The compounds were identified as (R)-lavandulyl acetate and neryl (S)-2-methylbutanoate by comparison with synthetic standards using gas chromatography (GC), GC mass spectrometry (MS), and chiral GC. Field trials were conducted with synthetic compounds in naturally infested crops of sweet pepper grown in large plastic greenhouses in Spain. The catch of adult females and males on blue sticky traps was increased by neryl (S)-2-methylbutanoate alone or by a 1:1 blend of (R)-lavandulyl acetate and neryl (S)-2-methylbutanoate, but (R)-lavandulyl acetate was not active alone. This is the first identification of an aggregation pheromone in the order Thysanoptera. The possible role of (R)-lavandulyl acetate is discussed.

Evidence for a male-produced sex pheromone in the western flower thrips Frankliniella occidentalis.

Olfactometer bioassays of walking adult western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) showed that virgin females (1- to 3-d postemergence) were attracted to the odor of 25 adult males, but not to the odor of 25 adult females, providing behavioral evidence for a male-produced sex pheromone in this species. In contrast to earlier findings, mixed-age adult males were attracted to the odor of adult males. GC analysis of odors collected on SPME fibers revealed two major components and five minor components that were present in the male odor and not in the female odor. The compounds were not present in hexane extracts of males, indicating that these compounds are produced on demand and not stored.

Analysis of anal droplets of the western flower thrips Frankliniella occidentalis.

Larvae of the western flower thrips Frankliniella occidentalis are known to produce an anal droplet containing decyl acetate (10Ac) and dodecyl acetate (12Ac), which act as an alarm pheromone. Analysis by GC showed that the combined mass of 10Ac and 12Ac per droplet increased with age of second instars from 2 ng to 18 ng, while the mass ratio of 10Ac:12Ac increased from 0.4:1 to 1.1:1 (molar ratio 0.4:1 to 1.2:1). Droplet volume increased from 0.4 nl to 2.1 nl with age, but only about 1% of this was accounted for by 10Ac and 12Ac. The remainder contained water. Analysis by GC-MS using SPME revealed no other volatile components. Whole bodies contained about two to four times as much 10Ac and 12Ac as a droplet, but in a similar ratio.