1a. Objectives (from AD-416)
To develop non-chemical alternatives to chemical fumigants for quarantine treatments of codling moth in fresh temperature fruits (apples and cherries) using low pressures (vacuum) at low temperatures.
1b. Approach (from AD-416)
We will: 1) study the control stability and precision of pressure, temperature, and humidity in low pressure (LP) chambers under empty and loaded conditions; 2) compare tolerance of eggs and larval stages under selected pressure and temperature combinations; 3) using the most tolerant life stage in fruit, conduct dose-response studies to determine the pressure, temperature, and exposure necessary to obtain probit 9 mortality levels; and 4) evaluate fruit quality under the LP treatment conditions required to achieve quarantine security (probit 9).
3. Progress Report
This research supports Objective 3 of the parent project, by providing data necessary to develop a quarantine treatment for codling moth infested fresh fruit (apples, pears and cherries) using a combination of low pressure, low temperature and high humidity. Using a computer simulation model, collaborators at Washington State University (Pullman) evaluated the pressure, temperature and humidity uniformity of laboratory scale hypobaric test chambers, and determined the optimal thickness of insulation needed to maintain the required temperature. The effect of various evacuation rates, venting rates, oxygen levels and leakage rates were also evaluated. In collaboration with scientists at the San Joaquin Valley Agricultural Sciences Center, preliminary studies to determine the most tolerant life stage of the codling moth to the treatment (4C, 10 mm Hg and nearly 100% RH) were done, with exposures of between 4 and 20 days. Contrary to what occurs with vacuum treatments at higher temperatures, codling moth eggs appear to be far less tolerant than larvae and pupae, and this appears to be due, at least in part, to their intolerance of 4C. Older (5th instar) larvae and pupae appear to be more tolerant to the treatment than young (3rd instar) larvae. Because little mortality in the more tolerant stages occurred after 20 days of exposure, subsequent studies will use treatment temperatures of 10C.