Estimating the Relative Abundance of Adult Citrus Root Weevils (Coleoptera: Curculionidae) with Modified Tedders Traps

Taylor’s power law (s2 = a x̄ b) was fitted to the means and variances of numbers of adult Diaprepes abbreviatus L. and Pachnaeus litus (Germar) caught monthly in modified Tedders traps (citrus Tedders traps). Data for D. abbreviatus were obtained in six Florida citrus groves, two located on the central ridge and the others in the central and southern flatwoods. Parameters for P. litus (a = 2.15, b = 1.17) using data pooled from two sites were consistent with parameters derived from the individual sites. Parameters derived from pooled data for D. abbreviatus were a = 2.69, b = 1.33; however, there was significant variability of the parameter b among sites. For specified levels of precision (confidence interval half-length:mean ratio), from 0–30% fewer traps were needed to estimate numbers of P. litus compared with D. abbreviatus at densities encountered in these groves. Plot size from 0.06 to >12 ha affected the numbers of traps needed to obtain monthly mean estimates of adult weevils per trap with a given level of precision. In general, sample precision was equal in large and small plots when population density in large plots was double that in small plots. At a given population density, ≈70% more traps were required in large compared with small plots to achieve a similar level of precision. Changes in trapped weevil abundance larger than 2.5-fold were detected as significantly different with the sampling plans used in these studies. Seasonality in the numbers of each species was evident at all sites (P = 0.05) because monthly means varied by 30- to 60-fold. In a separate study, the numbers of weevils recovered monthly from citrus Tedders traps were approximately congruent (r = 0.78, n = 33, P = 0.01) with numbers recovered from cone-shaped ground traps that only recover adult weevils as they emerge from soil. Annual maxima for both types of traps occurred at the same times during 33 mo, but each year weevil emergence from soil (as measured by cone traps) remained high for 1–2 mo after weevil recovery from citrus Tedders traps declined. Polynomial regression on monthly recovery from citrus Tedders traps explained 66% of the variation in monthly emergence of weevils from soil. Results of this study support the use of citrus Tedders traps in integrated pest management programs to detect the onset of emergence from soil by weevil cohorts, and to measure relative differences in weevil population density due to experimental treatments.