Thrips

Frankliniella occidentalis, Thrips

Frankliniella occidentalis, the western flower thrips, is a key pest of glasshouses, greenhouses and polytunnels.

Thrips can be difficult for growers to detect due to their small size and tendency for hiding within the concealed parts of the plant. Symptoms of plant damage by thrips include: bud deformation, shape distortion of fruits or vegetables during growth and a range of leaf spots and scars from thrips feeding. The larvae feed throughout the plant and leave the crop susceptible to secondary fungal and bacterial infection resulting in moulding and wilting.

Despite the small size of thrips at ~1mm in length the repercussions of Thrips infestations can be huge.

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OVERVIEW

Thrips have six main life stages which includes the egg, two larval, prepupal, pupal and adult stages. Eggs are laid on the underside of leaves, flower structures or fruit. In some cases this can result in wart-like growths but in others it is undetectable.

Larvae mature through two instars in concealed and well-protected plant parts such as within flower petals or under the calyx of fruits. In heavy infestations the larval will become mobile as they attempt to nourish upon all parts of the plant that are above ground. Most thrips, including western flower thrips, fall to the ground in order to pupate.

Finally, the adult thrips will emerge with slender and fringed wings in order to take flight and seek a partner for reproduction.

Research & Development

Optiroll Blue

Four years of large scale trials combining the application of natural enemies (mainly the predatory mite Neoseiulus cucumeris) and Optiroll special Blue sticky rolls have proved highly effective in bringing Western Flower Thrips under control.

Read more here: Optiroll Blue Research

Monitoring

Application Guidelines

The following notes are guidelines of general nature and meant to give the user a head start in implementing a Frankliniella occidentalis, Thrips monitoring program. Local conditions and practices can vary and can require customisation.

Recent Literature

Sampson, C. & Kirk, W. D. J. (2013) Can Mass Trapping Reduce Thrips Damage and Is It Economically Viable? Management of the Western Flower Thrips in Strawberry. PLOS One (2013)

The western flower thrips, Frankliniella occidentalis 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%. Damage that would result in downgrading of fruit to a cheaper price occurred when bronzing affected about 10% of the red fruit surface. 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.

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Sampson, C. & Kirk, W. D. J. (2012) Flower stage and position affect population estimates of the western flower thrips, Frankliniella occidentalis (Pergande), in strawberry. Acta Phytopathologica, 2012.

An accurate estimate of a population is essential for pest management. For Frankliniella occidentalis (Pergande) in strawberry, counts of thrips in flowers are commonly used as there is a strong correlation between thrips number per flower and fruit damage. The aim of this study was to look at the abundance and population structure of thrips within different flower stages and positions on the plant to test whether these affect population estimates. Adult females were found in open buds (petals showing), but were most frequent in young and mature flowers, whereas adult males were not found in buds and were most frequent in mature and senescent flowers. Twice as many adult thrips were found in mature flowers at the top of the plant compared to those at the side. Only larvae were found in closed buds (no petals showing). Larval numbers increased gradually with flower stage and peaked in senescent flowers. The choice of flower stage and position for sampling could affect population estimates by as much as a factor of four.

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