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. </p

Colour vision in thrips (Thysanoptera)

Insects are an astonishingly successful and diverse group, occupying the gamut of habitats and lifestyle niches. They represent the vast majority of described species and total terrestrial animal biomass on the planet. Their success is in part owed to their sophisticated visual systems, including colour vision, which drive a variety of complex behaviours. However, the majority of research on insect vision has focused on only a few model organisms including flies, honeybees and butterflies. Especially understudied are phytophagous insects, such as diminutive thrips (Thysanoptera), in spite of their damage to agriculture. Thrips display robust yet variable colour-specific responses despite their miniaturized eyes, but little is known about the physiological and ecological basis of their visual systems. Here, we review the known visual behavioural information about thrips and the few physiological studies regarding their eyes. Eye structure, spectral sensitivity, opsin genes and the presence of putative colour filters in certain ommatidia strongly imply dynamic visual capabilities. Finally, we discuss the major gaps in knowledge that remain for a better understanding of the visual system of thrips and why bridging these gaps is important for expanding new possibilities for applied pest management strategies for these tiny insects. This article is part of the theme issue 'Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods'

Visually and olfactorily enhanced attractive devices for thrips management

‘Lure-and-infect’ is an insect pest management strategy with high potential but so far there are few examples of its application. Using traps as surrogates for auto-dissemination devices, we tested the attractiveness to naturally occurring thrips (Thysanoptera: Thripidae) of three trap types differing in colour and structure, with and without the thrips lure methyl isonicotinate (MI), and sticky plate traps as a control. The aim was to find more effective traps that could be further developed into devices for auto-dissemination and lure-and-infect of thrips. The number of thrips captured varied substantially with trap type and the presence of the MI lure. We found a high visual response to a sticky ‘white ruffle’ trap (i.e., a 30-cm-long cylindrical outline of folded fabric), compared to a commonly used blue sticky plate trap (Bug-scan) as the control. This effect was seen both in a greenhouse with roses (Rosa spp.), where we encountered western flower thrips, Frankliniella occidentalis (Pergande), and in a grass field, where we encountered onion thrips, Thrips tabaci Lindeman, and New Zealand flower thrips, Thrips obscuratus (Crawford). In the absence of MI, the white ruffle trap caught 7–22× more thrips than the control Bug-scan trap. A similarly designed blue ruffle trap and a modified Lynfield trap caught lower thrips numbers than the white ruffle and the control Bug-scan traps. Presence of MI substantially increased the captures of T. tabaci in all three trap types in the field (2.5–18×). In the greenhouse, without MI the white ruffle trap caught 3.5–14× more thrips than the Bug-scan, blue ruffle, or modified Lynfield traps. Presence of MI increased the captures of F. occidentalis males and females in the Lynfield and blue ruffle traps (1.4–2.8×), but not in the white ruffle trap in the greenhouse (ca. 1.1×). The importance of visual and olfactory factors for the design of effective auto-dissemination and lure-and-infect strategies for thrips management is discussed.</p

Volatile compounds as insect lures: factors affecting release from passive dispenser systems

Knowledge about the behaviour of passive dispensers used to release semiochemicals for insect pest management is essential to ensure the efficacy of monitoring and control methods based on the use of the semiochemicals. The release characteristics of different passive dispenser types (commercial sachet, altered commercial sachet, polyethylene bags and cotton rolls) were investigated in the laboratory under various conditions. Using the volatile compound methyl isonicotinate (MI), a known lure for western flower thrips Frankliniella occidentalis (Pergande) and two additional homologues ethyl and n-propyl isonicotinate the effect of loading amount (0.5, 1.0 or 2.5 ml), temperatures (15°C, 25°C or 35°C) and air flow (0.1–0.15 m/s or 0.25–0.3 m/s) were tested in a low-speed laminar-flow wind tunnel. The results showed zero-order release kinetics for all tested dispenser types. Release rate kinetics relies on the type of molecule, dispenser type, and the climatic conditions with temperature being a major determinant of release rate. The results of the release characteristics of the different dispensers are discussed in regards to their practical use under greenhouse and field conditions.</p