Survival of Queensland fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) in apples treated with essential oils and cold storage

- Plant essential oils were tested against Bactrocera tryoni eggs and larvae in apple.
- Peppermint and broad-leaved peppermint oils have little potency for apple fumigation.
- They were effective at doses and exposure duration which were phytotoxic to apple.
- Cold storage was very effective against B. tryoni larvae and eggs in apple.
- The effect of cold storage was not enhanced by prior fumigation with essential oils.

Little is known on the fumigant effects of essential oils on the immature stages of fruit flies (eggs and larvae). The present study aimed to investigate effects of fumigation with essential oil alone or followed by cold storage on the survival of Queensland fruit fly Bactrocera tryoni in Gala apples. Efficacy was based on the number of pupae recovered from treated and untreated fruits and on phytotoxic effects. In a 24 h fruit fumigation test, peppermint oil applied at 100 and 200 μL/L air was found to be active against B. tryoni eggs, whereas broad-leaved peppermint oil was active against both eggs and larvae but only at the highest dose tested (200 μL/L air). However, both peppermint and broad-leaved peppermint oils sometimes had a phytotoxic effect on the apples. In a 6 h fruit fumigation test, an equal mixture of peppermint and broad-leaved peppermint oil (100 μL/L air) did not cause phytotoxic effect but had only a slight effect on B. tryoni eggs and no effect on the larvae. There was no synergism or additive effect when this essential oil mixture was applied in combination with subsequent cold storage. These results indicate that peppermint oil and broad-leaved peppermint oil have little potency for Gala apple fumigation since they were only effective at doses and durations of exposure which were phytotoxic to fruit. On the other hand, cold storage (4 ± 1 °C) alone was confirmed to be a very effective treatment against B. tryoni larvae and eggs in Gala apple without causing fruit damage and was not enhanced by prior fumigation with these oils.