The aim of the study was to check how the USA literature data about the correlation between: a)WCR population level and root damage rates; b)root damage rates and corn yield; c)WCR population level and corn yield, corresponds to the Croatian data in the conditions of low to moderate popluation level. The possibility of predicting the damages caused by WCR based on some of parameters (number of eggs in soil, number of emerged adults and root damage rate) was also checked. In 1998, the investigation was done in 6 continious corn fields in Vukovarsko-srijemska county. In 1999 and 2000 the investigations were done in continious corn field in Tovarnik. Number of eggs in soil was established by taking soil samples and by washing it in Spears equipment.To determine the number of emerged beetles per plant emergency cages were placed over corn plants.The root damage rates were established by digging, washing and rating roots after Iowa state scale (1-6). The yield was measured. In 1998, no eggs were found in soil samples. In 1999 an average of 3 eggs/sample, and in 2000 an average of 5 eggs/sample were found. The number of eggs per plant was predicted as 4,8 eggs per plant in 1999 and 7,8 eggs per plant in 2000. Number of beetles per plant was between 0 and 6,67. The average number of emerged beetles per plant was in 1999 17, and in 2000, 48. The root damage rates in 1998 were between 1,86 and 2,59, in 1999 between 2,38 and 2,9 and in 2000 between 2,83 and 5,66. The correlation coefficient between the number of emerged adults and root damage rate was r2=0,924. The regression line is described by the formel y=2,2+0,031x. Between the root damage rate and yield in 1998 a strong significant negative correlation was established. In 1999 full significant negative correlation was established. In 2000 no significant weak negative correlation was established. Because of low level of infestation and no significant correlation in 2000, the reggresion coefficient was not calculated. Comparing the results with US literature data, at this level of infestation we can conclude that the damages caused by WCR in Croatia are similar as in USA. For better understanding the relationships between different variables the investigations in the conditions of higher attack of WCR should be done.

correlation; Croatia; damage; Western Corn Rootworm

Published by University of Zagreb, Faculty of Agriculture, Zagreb, CROATIA
Sponsored by Ministry Science and Education of the Republic of Croatia