Climatic Data-Based Analysis of Boll Weevil (Coleoptera: Curculionidae) Overwintering Survival and Spring Emergence

Abstract

Analysis of data from a 15-yr study, composed of 97 boll weevil cohorts from overwintering habitats in the Rolling Plains of Texas, showed that overwintering survivorship and spring/summer emergence were influenced by the day of the year ( DOY ) when the weevils entered overwintering habitat ( DOY in), the amount of rainfall, and habitat temperatures experienced by the weevils during diapause. The earlier the date that weevils entered overwintering habitat or the greater the amount of rain occurring before emergence of the 1st weevil, the greater the positive degree-days (>6.1°C) required for weevils to emerge from overwintering habitat. There was no significant correlation between the timings of weevil emergence and the winter severity, measured in terms of negative degree-days(<0.0°C). Multiple least squares regression analyses describing the positive degree-days required for the weevils to start emergence ( DD start) and the time required for all weevils to emerge (duration of emergence) ( DD emerg) explained 88 and 77% of the variability in the data, respectively. With independent data, 75 and 36% of the variability were explained for DD start and DD emerg, respectively. Overwintering survival ranged from 0 to 50% in the 15-yr study. Survivorship was positively correlated with DOY in, and negatively correlated with NDD start and DD start. Multiple regression analysis with DOY in, negative degree-days, rainfall, positive degree-days, and their 1st order interactions explained 99% of the variability in overwintering survival. With independent data, 74% of the variability was explained by the survival function. A chi-square test for goodness-of-fit showed that 74% of the survival estimates did not differ significantly from their observed values. In contrast, when compared with independent data, 37% of the survival estimates did not differ significantly from their observed values. The spring/summer emergence pattern for the overwintering weevils was described by a sigmoid function that explained 95 and 92% of the variability for the verification data set and the independent data set, respectively. Boll weevil overwintering emergence patterns can be predicted with considerable accuracy, but greater knowledge of factors affecting boll weevil overwintering survival and the time to completion of emergence is required for these to be predicted accurately.