F. BACA, D. LOPANDIC
MRI, Zemun Polje, 11085 Belgrade-Zemun,
Yugoslavia
J. STEJCIC, V. TRKULJA
Institute of Agriculture, Banja Luka
S. RADANOVIC, DRAGICA ZIVANOVIC
Agricultural Station, BijeIjina
D. PARAVAC
Agricultural Station, Doboj, Republic
of Srpska
At least 200 mm of precipitation during the maize growing season are necessary for maize growth under rainfed conditions. Two-fold higher precipitation sum is considered satisfactory, while 500-600 mm are considered ideal. Effects of drought and high temperatures in the eastern regions of RS fill a role of stress in 2000. Temperatures induced earlier larval hatching in region of Semberia. The more precipitation sum approached the minimum value of 200 mm, the more unfavorable effects on maize and WCR were. On the other hand, precipitation and temperatures in 2001 were not a limiting factor in all regions of RS.
Monitoring of incidence and spreading of WCR imagoes over pheromone traps were done as in previous years. The obtained results were analyzed by comparison of the number of WCR imagoes over years and sums of precipitation and temperatures in BijeIjina, Doboj and Banja Luka. The favorable year of 1999 supported the development of the WCR population in 2000. Moreover, very warm April in 2000 with about 1500C HU accelerated larval hatching in maize continuous cropping in the area of BijeIjina; it also slowed down and reduced maize root development. Lack of nutrients and faster silk maturing resulted in significant WCR reduction in 2000 in comparison to 1999.
In 2001, the population increased by about 50% in relation to 2000 and equaled the abundance in 1999. The total number of imagoes per population amounted to 3532, 1972 and 3722 in 1999, 2000 and 2001, respectively.
Fluctuation of population abundance 2000:1999 and 2001:2000
| East-West | Distribution
1999 |
Distribution
2000 |
Distribution
2001 |
Years
2000:1999 |
Index
2001:2000 |
| < 50 km | 202.4 | 133.4 | 256.6 | 66 | 192 |
| 51-100 km | 43.0 | 58.5 | 94.8 | 136 | 162 |
| 101-150 km | 43.5 | 68.6 | 41.1 | 158 | 60 |
| > 150 km | 0.2 | 0.4 | 5.8 | 200 | 1450 |
The data obtained by imago monitoring in RS during 2000 and 2001 point out to a fact that a significant reduction of WCR population can occur in years with extreme weather conditions such as 2000 was. The population abundance increased westward.