ANTHROPOD PREDATORS AND HELIOTHIS SPP. IN COTTON, GOSSYPIUM HIRSUTUM L.: A COMPARISON OF THREE SAMPLING METHODS FOR DETERMINING SPATIAL DISTRIBUTION.

摘要

Three sampling methods were used to collect data on selected predators and Heliothis spp. in cotton to determine their spatial distribution and sampling method reliability. Predators sampled were: Geocoris punctipes (Say), Notoxus monodons (F.), Orius insidiosus (Say), Reduviolus roseipennis (Reuter) and spiders. The three sampling methods used were: bag capture, ground-cloth and terminal.; Predatory arthropod populations were relatively low in 1979 and 1980. Peak predator abundance occurred one month later in 1979 than in 1980. G. punctipes and N. monodons were the most abundant predators in 1979 and 1980.; Ground-cloth sampling proved significantly (p = 0.05) better than the bag capture or teriminal methods for estimating overall predator populations. Efficiency was based on the ability to detect numbers in sparse populations and also on low coefficients of variation (CV's). The CV's supported the results among sampling methods. The CV's for all methods were high and indicated large variations from the means.; Efficiency of sampling Heliothis spp. eggs was approximately equal using the bag capture and terminal methods. The mean number of eggs counted was similar and supports the observations on the ovipositional behavior of Heliothis spp. adults. The bag capture method was significantly better than the ground-cloth and terminal methods for sampling first-instar and small larvae. Both the bag capture and ground-cloth methods were significantly better than the terminal method for sampling large larvae. The CV's for the methods reflected the efficiency of the bag capture method over the ground-cloth and terminal methods.; Dispersion indices indicated that populations of predators were slightly clumped but less skewed than indicated by a negative binomial distribution. Ground-cloth sampling indicated the predators fitted the Poisson distribution. Notoxus monodons fitted the Poisson, Thomas double Poisson and Poisson with zeros distributions.; The spatial distribution of Heliothis spp. eggs was Poisson as indicated by the terminal method. However, the terminal method produced a larger number of data sets than did the bag capture method. Heliothis spp. first-instar, small and large larvae fitted the Poisson distribution best.