Temperature and Relative Humidity Effects on Eggs and First-Stage Larvae of the Black Vine Weevil,Otiorhynchus sulcatus12

Abstract

The effects of temperature and relative humidity on egg hatching, survival of first-stage larvae, and entrance into the soil by Otiorhynchus sulcatus (F.) were studied. Soil-surface temperatures under and outside strawberry foliage and the relative humidity under strawberry foliage were measured in the field. Newly-laid white eggs were more susceptible to extremes of temperature and relative humidity than they were after 3–4 days when they had become pigmented. Constant temperatures above 26.7° or below 15.6°C greatly reduced hatching. One or three exposures of three or six hours at 26.7° or 32.2°C interspersed with 15.6°C had less effect. Constant relative humidity of less than 65 percent reduced hatching to almost nil. A six- or 12-hour exposure to 33 percent RH during incubation at 85 percent RH had no effect. As many as 5-exposures to 33 percent RH interspersed with 85 percent RH had little effect. Survival of first-stage larvae was greatly reduced at relative humidity of less than 85 percent. The larvae would not enter layer of air-dried soil over moist soil, if the dry soil was over 15 millimeters deep, unless sufficient time was allowed for establishment of moisture gradient. Soil-surface temperatures and relative humidities under strawberry foliage would seldom harm eggs, especially those pigmented. Dryness of the soil surface could be serious detriment to newly hatched larvae.