Investigating the use of semiochemicals for integrated manage-ment of western flower thrips on stone fruit and table grapes

This research aimed to investigate the feasibility of using semiochemicals to modify thrips behaviour in order to minimize economic thrips damage, whilst reducing the need for toxic pesticides. The ultimate aim is to develop an effective, environmentally sustainable integrated management strategy for western flower thrips (WFT) on deciduous fruit crops by using a push-pull system. Three plant essential oils (methyl-salicylate, thymol and carvacrol) were identified from literature as potential oviposition deterrents.

Research objectives:

1. Test efficacy of methyl-salicylate, thymol and carvacrol to reduce WFT egg-laying in plum blossoms in laboratory bioassays.
2. Test efficacy of methyl-salicylate, thymol and carvacrol to reduce WFT egg-laying in plum blossoms in screen-house trials with potted plum trees.
3. Collect plum and clover flower volatiles by means of air entrainment.
4. Determine potential of clover as a trap crop for WFT: test attractiveness of with plum and clover flower volatiles by means of olfactometer trials.
5. Test push-pull system with semiochemicals and trap crop in field trials.

Laboratory bioassays showed that all three essential oils reduced the oviposition rate of WFT on plum blossoms, but methyl salicylate and carvacrol showed most promise because the lower concentrations of these oils (0.1%, 0.5%, 1%) reduced oviposition rates significantly without causing phytotoxic damage. This study is the first to show that these essential oils are effective in reducing WFT oviposition when applied to fragrant plum flowers. The inability of the wetting agents (Triton X-100 and Citrex® mineral oil) to keep the essential oils in stable suspensions was identified as a problem and this was confirmed by the lack of significant results in the screen-house and insectary trials using potted plum trees.

Plum blossoms and clover flower volatiles were successfully captured by means of air entrainment. Olfactometer studies showed that clover flower and plum blossom volatiles are highly attractive to WFT. This means that clover has potential as a trap crop for WFT, but it will only be effective if used in conjunction with an oviposition deterrent. The high level of attraction to WFT demonstrated for plum blossoms means that this holds true for any other potential trap crop.

Equipment procured and training received in air entrainment techniques during this study meant that Porapak Q tubes for air entrainment could be prepared and processed locally, instead of having to be obtained from and sent overseas for processing at significant costs. ARC Infruitec-Nietvoorbij is now also able to do air entrainment and prepare and process Porapak Q tubes for air entrainment as a service to other local researchers.

In conclusion, methyl salicylate and carvacrol show promise as oviposition deterrents for WFT on plum blossoms and clover would be suitable as a trap crop. At present, the lack of a suitable formulation for the oviposition deterrents is a limiting factor. However, if research on microencapsulation of essential oils is successful in providing a stable formulation with sustained release of behaviourally effective essential oil concentrations, implementation of a push-pull strategy to manage WFT in plum and other fruit orchards appears to be attainable.