S14 - Session O3 - Postharvest control of the grain chinch bug, Macchiademus diplopterus: physiological complexities and its impact on fruit export

Authors: Renate Smit *, Shelley Johnson

Postharvest mitigation treatments are one of the final measures in integrated pest management (IPM) of phytosanitary pests. Successful treatments require maintaining a balance between controlling the target pest and preserving fruit quality. The grain chinch bug ( Macchiademus diplopterus (Distant) (Hemiptera: Lygaeidae)) is a phytosanitary pest, endemic to the Western Cape, South Africa, requiring postharvest control. Previous studies have indicated that the grain chinch bug has the ability to become more tolerant of thermal stresses as they progress through aestivation. Insects were collected during different stages of aestivation and exposed to different cold storage regimes (standard cold sterilisation and dual temperature regimes) to examine the physiological state of the insect during commercially applied cold storage regimes. Early aestivating insects were more susceptible to cold storage, displaying higher levels of mortality than mid aestivation samples. Results from these studies provided insight into the physiological state of the grain chinch bug in response to potential low temperature phytosanitary treatments, and the limitations of low temperatures to control the grain chinch bug. The potential limitations of temperature treatments require investigation of alternative postharvest phytosanitary treatments, such as the use of fumigants. Consequently, the effect of ethyl formate as a fumigant was investigated as mitigation treatment against grain chinch bug, in combination with pome and stone fruit post treatment quality trials. Simulations from small desiccator trials to large container and cold room trials were used to determine viability of this technology as a postharvest phytosanitary treatment. Various stone and pome fruit cultivars were fumigated with ethyl formate using concentrations that successfully controls grain chinch bug with no phytotoxic effect. The ethyl formate concentration applied did not negatively affect fruit quality of the cultivars tested. Successful and sustainable mitigation treatments are crucial to continue and grow international trade of agricultural products.