Several authors have observed that Rhagoletis pomonella (Walsh) is usually less prevalent during hot dry summers than during cool wet summers (Rivard 1968). Neilson (1964) showed that the emergence of R. pomonella, under laboratory conditions, was affected by the relative humidity of the air. When the relative humidity was 20 or 40%, high mortality occurred during metamorphosis and fewer adults emerged.
The object of this study was to measure the influence of soil moisture on success and time of emergence in a laboratory experiment. The information is needed to improve the forecasting system for apple maggot control in apple orchards (Trottier, in press).