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 project was to support the parent project objective of developing alternative physical treatments for dried fruits, nuts, and fresh fruits. Codling moth, Cydia pomonella, is an important quarantine pest of fresh fruits such as apples, pears and cherries. The primary phytosanitary treatment used for exports to markets requiring quarantine protocols is fumigation with methyl bromide. Whereas quarantine and pre-shipment treatments with methyl bromide are currently allowable under the Montreal Protocol, there is growing concern that this exemption will eventually be lost. Consequently, alternative treatment protocols are being considered. Low pressure treatments, coupled with low temperatures and carefully regulated humidity, has been shown to prevent product deterioration caused by bacterial and fungal decay, and prevent wilting and fruit ripening during storage. This project looks at using these treatments to disinfest stone fruits of the various life stages of the codling moth. Lab-scale low pressure systems using aluminum chambers were used. Precise pressures and air exchange rates were maintained, and the humidity was kept near 100%. The air exchange system was important in maintaining humidity and removing metabolic plant products such as ethylene, which could negatively affect product quality. The insulated chambers were held in cold rooms set at the desired treatment temperatures. Temperature, pressure and humidity were recorded with electronic sensors sent to a computer control and recording system. Preliminary tests at 10 mm Hg and 10C were done to determine the codling moth life stage most tolerant to the treatment. Lab-reared eggs, 7 d old larvae, 14 d old larvae and pupae were compared. Temperature, pressure and humidity measurements showed that the low pressure system operated well within the desired limits. By adding 1.3 cm of foam insulation to the outside chamber walls, variation in chamber air temperature was considerably reduced, preventing condensation on the inner surface of chamber walls. Average relative humidity varied from 98.4-99.35%. In particular, the pressure regulators operated well with the air exchange system, providing a means to maintain high humidity levels and prevent ethylene build up while keeping pressure variations to a minimum. The egg stage appears to be the most susceptible to the low pressure, low temperature treatment, contrary to the results from earlier studies at 25 and 30C in walnuts. In preliminary tests, 100% mortality of the eggs was obtained after 20 days at 4C alone, whereas mortality for the larval and pupal stages ranged from 20-47%, suggesting that the low temperatures may be partly responsible for the relatively high egg mortality. Ten days at 10°C had little effect on egg hatch, but the low pressure treatments, even the shortest exposure, resulted in high mortality. The relatively high tolerance of the larvae and pupae may be due to the high humidity of the treatment. In earlier studies treatments were done at about 60% relative humidity, and larvae were found to be more susceptible to low pressures at lower humidity levels. The response of larvae and pupae to the treatment was similar, although 14 day old larvae were slightly more tolerant. Insect mortality increased with increasing treatment time to more than 98% after 12 days of exposure. Weight loss, color, firmness, titratable acidity, and soluble solids content were selected as quality parameters to evaluate the quality changes of ‘Red Delicious’ apples before and after the low pressure treatments. The measured quality of ‘Red Delicious’ was maintained well after 15 days of exposure to low pressure conditions at 10C, suggesting that this technology has potential as an alternative non-chemical disinfestation treatment method for apples, reducing the need for chemical fumigants while maintaining product quality and extending shelf life.