LP-p and LT-p lines of insekticides for Bothynoderes punctiventris Germ. at different air temperatures

Abstract

The effects of insecticides monocrotophos, cypermethrin and their ready -made mixtures applied against sugar beet root weevil (B. punctiventris G e r m) adults at different temperatures were studied. The experiments were conducted in laboratory conditions at three different temperatures: 14, 20 and 25°C. In 1996 and 1997, the adults used in experiments were collected in Bačka Topola fields with sugar beet as previous crop. The adults were exposed to insecticides by method of insecticide soaked blotting paper and fed with sugar beet cotyledons. The mortality of adults, depending on product was observed every half an hour, starting from 0.5 up to 28 hrs of exposition. Applying probit analyses, ld-p and lt-p lines were constructed, which reflected the changes of toxity depending on insecticides and temperatures. According to position and slope (b) of ld-p lines in 1996, higher toxity of cypermethrin than of monocrotophos was found. The response was more homogeneous to cypermethrin than to monocrotophos. Ld-p lines for mixture run closer to ld-p line for cypermethrin independent of temperature. In 1997, at 14°C and 25°C, higher toxity of cypermethrin than of monocrotophos was observed, the effect of mixture was additive. No mortality was induced with monocrotophos at 20°C. The reason could be in sugar beet root weevil population sensitivity decrease to monocrotophos in 1997, or the insects derived from two different populations exposed to different selection pressure (species, volume and exposition length to insecticides). Based on lt-p lines in both experimental years, it could be concluded that cypermethrin, independent of temperature had higher initial toxity than monocrotophos, the mixture achieved additive effect, except in 1996 at 20°C where the effect was synergised compared to single component effects.

Keywords

• sugar beet root weevil
• insecticides
• temperature
• ld-p
• lt-p lines