The determination of biological criteria the basis to struggle alfalfa weevil, hypera postica (Gyllenhal, 1813) (Coleoptera: Curculionidae) on alfalfa in Iğdır province

This study was conducted to determine biology in nature, infestation of adult, pupae and larvae in square metre with biological criteria the basis to struggle of alfalfa weevil, Hypera postica (Gyllenhal, 1813) (Coleoptera: Curculionidae) in alfalfa field of Iğdır province in the years 2014-2016. Biological observation performed once a week in spring period, monthly in winter and every 15 days in other months. Insecticide trials were established to be repeated four times in random order blocks trial design order, and optimal chemical control was determined based on plant height and insect's biology. According to the study results, new generation adult of H. postica was observed as from 3rd week of April and it was found that the first eggs were laid within the plant scapus from the first week of November, when the average temperature was 10.5 °C. The insect hibernated in adult and egg stages and overwintered adults were laid their spring eggs in stem of alfalfa at an average temperature of 13 °C towards the end of March. The first larvae were detected in the begining of March that average temperature was 9.1 °C and the first pupae in the begining April that average temperature was 13.6 °C. Hypera postica produce a generation per year in climatic condition of Iğdır. As a result of insecticide tests in different periods (5, 10, 15 and 25 cm plant height and control), the yield of wet grass were 1213.43 kg, 880.50 kg, 889.19 kg, 802.38 kg and control 763.75 kg, respectively. The highest yield was obtained from spraying while the plant height of alfalfa was 5 cm . Key Words: Alfalfa, Alfalfa weevil, Biological criteria, Insecticide, Time of Chemical Control.