Estimating the relative abundance of adult citrus root weevils (Coleoptera: Curculionidae) with modified Tedders traps

Taylor's power law (s(2) = a (x) over bar (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 loc ated on the central ridge and the others in the central and southern flatwo ods. Parameters for P. litus (a = 2.15, b = 1.17) using data pooled from tw o 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 si tes. For specified levels of precision (confidence interval half-length:mea n ratio), from 0-30% fewer traps were needed to estimate numbers of F. litu s compared with D. abbreviatus at densities encountered in these groves. Pl ot 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 pre cision. In general, sample precision was equal in large and small plots whe n population density in large plots was double that in small plots. At a gi ven population density, approximate to 70% more traps were required in larg e compared with small plots to achieve a similar level of precision. Change s in trapped weevil abundance larger than 2.5-fold were detected as signifi cantly 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 o f weevils recovered monthly from citrus Tedders traps were approximately co ngruent (r = 0.78, n = 33, P = 0.01) with numbers recovered from-cone-shape d ground traps that only recover adult weevils as they emerge from soil. An nual 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) rema ined high for 1-2 mo after weevil recovery from citrus Tedders traps declin ed. Polynomial regression on monthly recovery from citrus Tedders traps exp lained 66% of the variation in monthly emergence of weevils from soil. Resu lts of this study support the use of citrus Tedders traps in integrated pes t management programs to detect the onset of emergence from soil by weevil cohorts, and to measure relative differences in weevil population density d ue to experimental treatments.