Mortality of kiwifruit pests (Coccoidea) exposed to ethyl formate delivered using either carbon dioxide or nitrogen carrier gases

Abstract

Ethyl formate (EF) is used as a fumigant against insect pests on many commodities. Delivery of EF uses a carrier gas, usually carbon dioxide (CO 2 ), to reduce its flammability. However, CO 2 is expensive and can only be delivered relatively slowly. Nitrogen (N 2 ) has been proposed as an alternative. The efficacy of EF delivered using CO 2 or N 2 , was evaluated at 5 and 15°C, against two important postharvest pests of kiwifruit (greedy scale (Hemiberlesia rapax, Hemiptera: Diaspididae) and obscure mealybug (Pseudococcus viburni, Hemiptera: Pseudococcidae)). Mortalities of both insect species were higher in the presence of CO 2 than N 2 . There was a strong interaction with treatment temperature: N 2 at 5°C resulted in low mortality across both species. Greedy scale was more susceptible to EF than obscure mealybug across all treatments. Nitrogen as a carrier gas for EF substantially lowered the efficacy of EF as an insecticidal fumigant, relative to CO 2 . This is hypothesised to be caused by differing respiration rates across temperatures and CO 2 concentrations. Solutions for rapid CO 2 delivery should be explored over further trials with N 2 at low temperatures.