postharvest alternatives to methyl bromide

Controlled Atmosphere

Controlled atmosphere (CA) treatments typically involve manipulating the ratio of gasses (typically, oxygen, carbon dioxide and nitrogen) in the environment, and/or the ambient temperature. This type of treatment is an attractive alternative for postharvest insect control, as it provides a non-chemical treatment that leaves no residues. For some commodities, such as the dried fruits and nuts, exposure to controlled atmospheres can be beneficial in maintaining product quality as well as controlling insect pests. CA treatments can potentially be accomplished in marine containers during the voyage to distant export markets. This is important for timely marketing, as many of the CA treatments require several days to weeks for efficacy against target pests.

Controlled Atmosphere Studies

Summary of CA for arthropod control on fresh horticultural perishables (pdf)
Elizabeth J. Mitcham, TunyaLee, A. Martin, Shijun Zhou and Adel A. Kader
2003
The literature on controlled atmospheres (CA) for arthropod control on fresh horticultural perishables is summarized. Four basic approaches to control of arthropod pests are discussed, including regular CA storage, low temperature insecticidal CA, room temperature insecticidal CA, and high temperature insecticidal CA. Insecticidal CA (ICA) generally involves oxygen (O2) concentrations below 2kPa and/or CO2 concentrations of 20 kPa or greater.

The mode of action of insecticidal controlled atmospheres (pdf)
E. Mitcham, T. Martin and S. Zhou
2006
When O2 in the environment is reduced, insects lower their metabolic rate. Subsequently, to meet their basic energy requirements, anaerobic metabolism is initiated. Both the accumulated anaerobic end products and the very low metabolism impose stress on the insects. Studies have concluded that the O2 level needs to be below 3% for this stress to be lethal; in most cases, it needs to be below 1% for rapid kill. The additonal factors of humidity and temperature have a great effect on mortality in low oxygen environments. At low humidity, reduced O2 causes rapid water loss through opened spiracles. At higher temperatures, susceptibility to controlled atmospheres is greater due to enhanced respiratory demand. However, a high or low temperature outside the optimum range for the arthropod, can be an added stress.