Low-dose methyl bromide fumigation as a quarantine treatment against Queensland fruit fly to improve exports of Australian capsicums

Abstract

Capsicums (Capsicum annuum) were fumigated with methyl bromide (MB) at a nominal treatment dose of 18g m-3 at 18°C for 5 hours as a quarantine disinfestation treatment against Bactrocera tryoni, the Queensland fruit fly. Three large scale trials were conducted against each of the four immature lifestages, eggs and first, second and third instars. There were no survivors from the estimated 35,551 eggs, 53,720 first instars, 40,371 second instars and 43,901 third instars treated in capsicums, thereby resulting in an efficacy of >99.99% mortality at the 95% confidence level for each lifestage.

Commercial fruit were also fumigated under the same conditions and then held at 6°C for 16 days or 6°C for 10 days followed by 10°C for 6 days. This was to simulate transport at 6°C followed by retail display at 10°C. Fruit quality parameters of weight loss, total soluble solids and external quality including, visual appearance, skin wrinkling, skin pitting, and incidence and severity of rots were assessed and no significant adverse treatment effects were present.

This research aims to develop a new protocol for the export of Australian capsicums to New Zealand as an alternative to the current protocol of 40g m-3 MB for 2 hours at 17°C. The new protocol uses half the concentration of fumigant but applied for double the treatment time to maintain the efficacy against Queensland fruit fly a significant quarantine pest in Australia. Whilst the reduction in quantity of MB used is environmentally beneficial, the research was primarily undertaken to improve out-turn quality of the treated capsicums. The existing protocol impacts fruit quality while the lower dose tested in our research had no significant effects on the range of fruit quality attributes tested.