IN recent years chilli thrips have become an issue in commercial orchards in West Gingin and Carnarvon. Common to both sites has been infested orchards located adjacent to other host crops that also have fruit damaged by chilli thrips. This is similar to overseas experiences, however, in Florida, there has only recently been chilli thrips issues in citrus nurseries and in citrus grown under protective screen (CUPS) despite the pest being present for many years in other crops such as strawberries and blueberries. Chilli thrips have been present in Australia for many years, mainly in northern WA, QLD and NSW. In the eastern states, records from the 1990s describe the thrips as an occasionally important pest of citrus.

Damage
Chilli thrips are sap-sucking insects that can injure the developing flowers, fruit and leaves of citrus, causing similar looking damage to other pest thrips species and mites.

Ring scaring around the stem end of fruit is characteristic of chilli thrips. Scarring can extend down the sides of fruit where infestations are high. Heavy infestations can also cause twisting and grey scaring of foliage (Figure 1). Chilli thrips feed on tender plant parts — there are no reports of them feeding on mature plant tissues.

Interstate and overseas, outbreaks and associated damage have mainly occurred during the spring flush and flowering.

Lifecycle
The chilli thrips life cycle, comprising egg, larva, pre-pupa, pupa, and adult (Figure 2), lasts from 15–40 days depending on temperature and host plant. Eggs are laid into soft plant tissue, and each female can lay 60–200 eggs! With around 13 generations possible in the Perth climate, populations can quickly escalate (Figure 3). The thrips can survive at minimum temperatures as low as 9.7°C and maximum temperatures as high as 33.0°C.

Yellow sticky traps can also be used to monitor for thrips. A (10x) hand lens, and white board can help to see thrips and count them. Site for monitoring may include borders and a 'W' pattern through the orchard to find any hot spots. Consistency in sampling means that results can be compared from week to week to spot any trends, for example in number of thrips per sample.

Chilli thrips have a wide host range so understanding the level thrips in surrounding hosts may also be important.

Early targeted action based on the thrips lifecycle appear to be key to managing this pest.

To better understand the abundance of chilli thrips in citrus orchards, between August and November this year, 4 Masters students from Edith Cowan University are working with WA Citrus and WA orchards.

Overseas, management for chilli thrips in field crops, when required, is normally based on pesticides. However chilli thrips can develop resistance to pesticides so their use should be kept to a minimum. This might mean by only treating hot spots and borders and ensuring good coverage by calibrating sprayers and application. Perimeter sprays may be beneficial where orchards adjoin highly susceptible host crops. IPM friendly formulations of pesticides should also be considered, being careful to rotate modes of action as thrips are notorious for developing insecticide resistance.

Chilli thrips have many natural predators, including mites, bugs, lacewings, and other thrips, however when chilli thrips numbers are very high, they can become quickly overwhelmed. Natural predators in the crop can be protected with targeted control of the chilli thrips rather that cover-all treatments. The role of natural enemies against chilli thrips in citrus orchards has not been determined.

Control strategies using predictive models may be developed as we gain more knowledge on the interaction of the chilli thrips life cycle in conjunction with climatic variables and crop species.

Complementary research in WA on chilli thrips by Murdoch in blueberries and an APC/DPIRD/CRC project for citrus, table grapes, vegetables and strawberries will also assist with understanding the damage thresholds, role of natural enemies and resistance.