engleski

Population dynamic and sex ratio of cabbage stem flea beetle in Croatia

After the neonicotinoid restriction by the European Commission (485/2013) which banned the use of imidacloprid, clothianidin and thiamethoxam on flowering crops including oilseed rape, pests that appear in autumn have become an increasing problem, especially the cabbage stem flea beetle (Psylliodes chrysocephala L., 1758). Adult forms feed on the leaves and make characteristic ‘shot- holing’ damage similar to cabbage flea beetles (Phyllotreta sp.) but damage is not usually significant. The most significant damage is caused by the larvae that feed inside leaf petioles and stems. They make feeding tubes inside the plant and during winter period can frost causing cracking of plant tissue (Alford et al., 2003 ; Williams, 2004). To gain an insight into the phenology and occurrence of this pest in Croatia, the aim of this research was monitoring of the pest population and determination of the sex ration of adult forms. This investigation was conducted during autumn 2017 and spring 2018 on the experimental station of the University of Zagreb Faculty of Agriculture (45°50'59''N 16°11'12''E). Population dynamics of adult forms of cabbage stem flea beetle was monitored using yellow water traps during 2017. Four yellow water traps were placed diagonally in the field on August 29 (before sowing of the oilseed rape on September 9) and were emptied once a week. Monitoring was finished on April 25 at the beginning of flowering (BBCH 63). Adult forms of cabbage stem flea beetle were identified and separated by gender according to differences in first tarsal segment of the front and middle pairs of legs ; the first tarsal segment of females is smaller and more regular in size compared to the other segments and the first tarsal segment in the male is triangular-shaped and larger than other segments (Bonnemaison & Jourdeuil, 1954 cit. Cook et al., 2006). During the period of investigation, 225 adult forms of cabbage stem flea beetle were recorded in total. Activity of adults was recorded from September 5 until March 21. The first adults were recorded on September 5, even before sowing of the oilseed rape, which was the peak of the flight at the same time. Second peak flight activity was recorded on October 10 at GS BBCH 15 (Lancashire et al., 1991) (five oilseed rape leaves unfolded). Both genders of cabbage stem flea beetle appeared simultaneously except in the second peak flight activity when higher number of males was recorded.

cabbage stem flea beetle, population dynamic, sex ratio

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