Flight performance of laboratory-reared adults of the plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), was investigated under controlled conditions by using a flight mill system. Across all insects tested (n=198), median values of total distance traveled, total flight time, and maximum uninterrupted flight time were 122.7 m day(-1), 23.5 min day(-1), and 2.0 min, respectively. The latter result indicates that flight occurred primarily in short bursts. Although females had a significantly higher body mass than males, there were no significant differences in flight performance between the two sexes. Flight during the first 24-h test period (especially the first 6 h) was dominated by escape behavior, i.e., elevated levels of activity presumably associated with attempts by the insects to regain freedom of movement; during the second 24 h, flight activity was very limited throughout the late morning and afternoon, increased around sunset, and remained high during the night. All flight performance variables decreased linearly and significantly with insect age over the age range tested (2-16 d after emergence). Nutritional status also had a significant effect, whereby insects that had been provided with apples as a food source for 2 d after emergence showed considerably improved flight performance compared with those that had been given no food or only water during the same period. There was no significant effect of mating status on flight performance of male or female insects.
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 ~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 (~30%) and dry (~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 ~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 ~2.8 kPa. Cuticular permeability of C. nenuphar to water was calculated as 185.8 μg cm−2 kPa−1.
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