Implications of changes in arthropod distribution following chemical application
The influence of pesticide application on the within-field distribution of arthropods was investigated forTetranychus urticae, the twospotted spider mite, on strawberries. Analyses of dispersions based onGreen's coefficient,Iwao's regression of mean crowding on the mean, andTaylor's power law all indicated that mite populations were highly aggregated initially. As densities increased, more of the avialable niches were filled, leading to a less clumped dispersion. However, pesticide applications causing greater than 99.9% mortality acted in a nearly density independant fashion and, although the originating populations were similar in number, did not produce dispersions equivalent to the initial migrants. As a result, ignoring these changes by developing sampling plans based on dispersion indices which generated a single slope for an entire data set, led to statistical errors that invalidated the sampling programs. In order to accurately reflect the field biology of the spidermites, sampling plans for pre and post-treatment populations were substantially different.
The impact of such changes in dispersion were graphically demonstrated using both sequential and binomial sampling techniques. Both methods showed that fewer samples were necessary to estimate densities at a given precision level for post-treatment populations. Also, these techniques indicated that post-treatment populations had similar, but significantly different, dispersions. The implications of changes in pre and post-treatment dispersions, as well as problems associated with inconsistant dispersions following pesticide use, are discussed.
KeywordsSampling Plan Active Stage Pesticide Application Precision Level Binomial Sampling
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- Carey, J. R. andJ. M. Bradley (1982) Developmental rates, vital schedules, sex ratios, and life tables forTetranychus urticae, T. turkestani andT. pacificus (Acarina: Tetranychidae) on cotton.Acarologia23: 333–345.Google Scholar
- Green, R. H. (1966) Measurement of nonrandomness in spatial distributions.Res. Popul. Ecol.8: 1–7.Google Scholar
- Green, R. H. (1970) On fixed precision level sequential sampling.Res. Popul. Ecol.12: 249–251.Google Scholar
- Iwao, S. (1970) Problems of spatial distribution in animal population ecology. 117–149. InG. P. Patil (ed)Random counts in scientific work, Vol. 2. Penn. State Univ. Press, Univ. Park, Pennsylvania.Google Scholar
- Iwao, S. andE. Kuno (1971) An approach to the analysis of aggregation pattern in biological populations. 461–513. InG. Patil, E. Pielou andE. Waters (eds)Statistical ecology, Vol. 1. Penn. State Univ. Press, Univ. Park, Pennsylvania.Google Scholar
- Myers, J. H. (1978) Selecting a measure of dispersion.Environ. Entomol.7: 619–621.Google Scholar
- Oatman, E. R., J. A. Wyman, H. W. Browning andV. Voth (1981) Effects of releases and varying infestation levels of the twospotted spider mite on strawberry yield in southern California.J. Econ. Entomol.74: 112–115.Google Scholar
- Ruesink, W. G. (1980) Introduction to sampling theory. 61–78. InM. Kogan andD. Herzog (eds)Sampling methods in soybean entomology.Springer-Verlag, New York, New York.Google Scholar
- Shepard, M. (1980) Sequential sampling plans for soybean arthropods. 79–93. InM. Kogan andD. Herzog, (eds)Sampling methods in soybean entomology. Springer-Verlag, New York, New York.Google Scholar
- Taylor, L. R. (1965) A natural law for the spatial distribution of insects.Proc. XII International Congress of Entomology. pp 396–397.Google Scholar
- Trumble, J. T. andE. R. Oatman (1984) Dispersion analyses and resource utilization of aphid parasitoids in a non-depletable environment.Res. Popul. Ecol.26: 124–133.Google Scholar
- Trumble, J. T., E. R. Oatman andV. Voth (1983) Temporal variation in the spatial dispersion patterns of aphids (Homoptera: Aphididae) infesting strawberries.Environ. Entomol.12: 595–598.Google Scholar
- Trumble, J. T., H. Nakakihara andV. Voth (1984) Development and evaluation of a wax immersion technique designed for studies of spider mite (Acari: Tetranychidae) population on strawberries.J. Econ. Entomol.77: 262–264.Google Scholar
- Walker, G. P., I. V. Madden andD. E. Simonet (1984) Spatial dispersion and sequential sampling of the potato aphid,Macrosiphum euphorbiae (Homoptera: Aphididae), on processing tomatoes in Ohio.Canad. Entomol.116: 1069–1075.Google Scholar
- Wilson, L. T. andP. M. Room (1983) Clumping patterns of fruit and arthropods in cotton with implications for binomial sampling.Environ. Entomol.12: 50–54.Google Scholar