Population, spatial distribution and biology of cereal leaf beetle, Oulema melanopus L. Col.: Chrysomelidae, in winter wheat fields of Gorgan

Cereal leaf beetle (Oulema melanopus L. (is one of the major pests of cereals, particularly winter wheat, in Golestan province, northern Iran. Population density, spatial distribution and biology of this pest were studied in wheat fields of Gorgan region, during two agricultural seasons of 2006 and 2007. Emergence time and peak of the pest activity differed in different regions. In general, the first adults were emerged from hibernation sites in the mid of February and peaked in the mid of March. The maximum mean of adult beetle was estimated 15.07±0.8 per sweep net. The first oviposition was observed in the early of March and the maximum number of eggs was 17.53±1.9 per quadrate. The activity of larva population was started from the late March and reached to the peak level by the early May. The maximum counted number of larvae was 16.9±0.9 per quadrate. The Taylor’s power law and Iwao’s patchiness regression coefficients for different developmental stages of the pest were equal to 1, statistically indicating that O. melanopus populations were randomized. Also, the using of mathematical distribution models showed the adult and the larva populations dispersion dispersion were randomized during most of the growing season. However the spatial distributionof eggs was not fittedwith poisson model. The mean duration of incubation period, total developmental time of the larval stages and pupa in the field conditions were of 8.05±1.02, 29.23±1.03 and 12.29±1.17 days, respectively. These results can provide a reliable basis to develop proper sampling plans for estimating or classifying natural enemy populations in wheat fields of northern Iran.