SPATIAL PATTERN AND DENSITY OFCTENICERA DESTRUCTORANDHYPOLITHUS BICOLOR(COLEOPTERA: ELATERIDAE) IN SOIL IN SPRING WHEAT

Abstract

Determination of the spatial pattern and estimation of the density of egg, larval, and adult populations ofCtenicera destructor(Brown) andHypolithus bicolorEschscholtz were made by soil sampling, and forC.destructoradults, also by cages that collected the emerging adults in the spring. Eggs of both the above species and also those ofAeolus mellillus(Say), which were also found in the samples, were highly aggregated. SmallC.destructorlarvae were most highly aggregated and medium larvae less so; large larvae were usually randomly distributed. UnlikeC.destructor, largeH.bicolorlarvae were more highly aggregated than either the small or mediumbicolorlarvae. Sampling by emergence cages showed thatC.destructoradults were aggregated while sampling by soil cores showed them to be randomly distributed. The different result obtained by the two methods was attributed to the difference in the size of the sampling unit. Aggregation was detected in 29% of theH.bicoloradult population sampled by soil cores only.Larval densities ofC.destructorranged from a low of 0.25 to a high of 1.46 per sample unit (81 cm²) over the 14-year period that samples were taken; densities ofH.bicolorranged from 0.16 to 0.64. Densities ofC.destructorandH.bicoloradults averaged about 6 (range 1–16) % and 12 (0–27) % of the total population of larvae and adults for each respective species. Population composition, in terms of adults and larvae of different sizes, and population fluctuations are discussed.The relation between density and the number of sampling units required to achieve four levels of margin of error at four levels of statistical significance was determined.No satisfactory transformation was found for data of individual samples with a mean less than 1. Several common transformations, including Taylor’s power transformation, were satisfactory for stabilizing the variance of pooled samples.