William D. J. Kirk

The spread of the western flower thrips Frankliniella occidentalis (Pergande)

Abstract  1 Since the late 1970s, the western flower thrips has spread from its original distribution in western North America to become a major worldwide crop pest.

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.

The size relationship between insects and their hosts

Abstract. 1 Regressions of adult insect size on host size were tested. The analysis was restricted to highly host‐specific insects that had thus been exposed to a narrow range of host size. 2 The phylogenetic regression method was used to analyse the data, so as to allow for the possible phylogenetic effects in cross‐species data. 3 Significant positive regressions were found in all the groups tested: female flower thrips, Meligethes species of pollen beetle, tephritid flies, and male and female fleas. They were also found by standard regressions within. and between Actornithophilus species of bird louse. 4 The regression of thrips size on pollen size was not significant, providing evidence against a hypothesis involving food size. 5 The regression of flea body size on host hair/feather length was significant, which is consistent with a hypothesis involving the size of spaces on the host. 6 The relationships may have implications for the understanding of evolutionary host shifts.

Factors affecting floral herbivory in a limestone grassland

Abstract The amount of herbivore damage to the petals of 41 species of herbaceous plant was surveyed from April to September in a limestone grassland in central England. Damage was recorded as the percentage of the petal area removed. Most damage was caused by invertebrates, particularly slugs. The amount of invertebrate damage differed significantly between plant species and with time of year. The mean damage across all species was only 2 %, ranging from an average of 0 % in Galium sterneri to 8 % in Primula vulgaris. In most species, less than a quarter of flowers received any damage, so those that were damaged were often severely affected. Species flowering early or late in the season received more damage, possibly because of greater slug activity. Hypotheses to explain the inter-specific variation in the amount of herbivory were examined by testing for correlations with a range of plant variables. No correlations with flower-stem length, flower-stem thickness or the longevity of flowers were apparent. The amount of petal damage correlated strongly with flower size and petal thickness. This appeared to result from the prevalence of large-flowered species early and late in the season rather than from a preference for flower size and petal thickness per se. The evolutionary significance of floral herbivory is discussed.

A key to the second instar larvae of the Thripidae of the Western Palaearctic region (Thysanoptera).

When studying Thysanoptera, specimens of the adult stage are most commonly encountered. Identification keys to the nearly 6000 described species, based on morphological features of these adults, are available for several regions of the world, for example a key to the species of Europe and the Mediterranean Area (Zur Strassen 2003). There are also several keys to the pest species of the world (Palmer et al. 1989, Mound & Kibby 1998, Moritz et al. 2001). However, when studying subjects such as host-plant relationships, faunistics or pests in international trade, it is common that only larvae are available, and identification of these is hampered by the lack of keys to immatures. In particular, immatures of the large suborder Terebrantia are often collected, but can only be identified with molecular identification techniques or after rearing to the adult stage. The Thysanoptera have two active immature stages, known as larva I and larva II, and two or three quiescent immature stages, known as propupa, pupa I and pupa II. The third quiescent stage, pupa II, occurs only in the family Phlaeothripidae. Although Thysanoptera are exopterygote, having wing pads in the quiescent stages, there is extensive replacement of juvenile structures with adult structures during the quiescent stages. This means that they are effectively holometabolous and so it is appropriate to use the terms “larva” and “pupa” for the immature stages, rather than the term “nymph” (Nüesch 1987, Richards & Davies 1977, Moritz 1997). This terminology is used throughout the literature on Thysanoptera. The larvae have been described for some common or pest species of Terebrantia, but there are almost no descriptions of the pupae. Larvae and pupae are easily overlooked because they are so small, but the pupae are even less often encountered because they occur typically in the soil or hidden within recesses on plants. Most studies of immature thrips stages have focused on the second instar larvae, since these A key to the second instar larvae of the Thripidae of the Western Palaearctic region (Thysanoptera)

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.

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.

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.

Effects of alarm pheromone on landing and take-off by adult western flower thrips

Kenneth M. MacDonald1, James G.C. Hamilton1, Robert Jacobson2 & William D.J. Kirk1,∗ 1School of Life Sciences, Keele University, Staffordshire ST5 5BG, UK; 2Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK (Current address: Stockbridge Technology Centre, Stockbridge House, Cawood, Selby, North Yorkshire YO8 0TZ, UK); ∗Author for correspondence (E-mail: w.d.j.kirk@keele.ac.uk)

The effect of photoperiod on walking, feeding, and oviposition in the western flower thrips

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest in glasshouses, where light and photoperiod are often manipulated to grow crops. The effect of five photoperiods (L0:D24, L6:D18, L12:D12, L18:D6, and L24:D0) on the behaviour of adult females was investigated in the laboratory at 25 °C. The amount of walking, pollen consumption, and oviposition all increased with increasing photophase. The three behaviours occurred at a low rate in continuous darkness, and are therefore not exclusively diurnal. Three out of 16 thrips (19%) showed weakly rhythmic walking activity in continuous darkness, with an average circadian period of 25.3 ± 1.5 h. It is proposed that the length of the photophase determines the amount of nutrient intake, which in turn determines oviposition rate and thus affects population increase.