Moisture effects on development and survival of the plum curculio (Coleoptera: Curculionidae)

Laboratory-reared larvae of Conotrachelus nenuphar Herbst were exposed to three soil moisture treatments in pots containing a mix of soil and vermiculite, whereby pots were either watered daily (wet treatment) or watered to saturation when matric potential reached threshold values of -160 and -800 kPa for the intermediate and dry treatments, respectively. Adult emergence began at approximately the same time in the 3 treatments, but peak emergence (occurring [approximately]1 month after the start of the experiment and within 2 wks of the beginning of emergence) was much more pronounced in the intermediate moisture treatment than in the wet and dry ones. In addition, cumulative emergence in the intermediate moisture treatment (corresponding to >40% of the initial number of larvae used in the experiment) was higher than in the wet ([approximately]30%) and dry ([approximately]20%) treatments. Approx. 25% of the adults that emerged from the dry treatment were underdeveloped and/or malformed. In a separate set of experiments, the effect of air humidity on survival of laboratory-reared plum curculio adults was investigated. Survival analysis revealed a significant (P 0.0001) effect of vapor pressure deficit on adult longevity. As vapor pressure deficit decreased from [approximately]2.8 to 0.009 kPa, median life expectancy increased from 1.1 to 9.0 d for insects without food supply and from 7.0 to 30.5 d for insects feeding on apples. Longevity correlated with cumulative water loss from the insects, which was lowest in a saturated atmosphere and greatest for insects exposed to a vapor pressure deficit of [approximately]2.8 kPa. Cuticular permeability of C. nenupharto water was calculated as 185.8 [mu]g cm-2 kPa-1.