Contribution to the study of biology of ASH weevil (stereonychus fraxini de geer)

Abstract

One of the most harmful defoliating insects on ash species in Southeast Europe is the ash weevil (Stereonychus fraxini De Geer). Frequent occurrence of ash weevil outbreaks initialed research of the biology of this insect. The aim was to study the less known parts of insect biology, such as time of the insects development in natural conditions, fertility and fecundity of females, the duration of the embryonic, larval and pupal development, the amount of food consumed by larvae and adults. Research of insect development in nature conditions were carried out during 2008 and 2009 in the forests Branjevina near the town Odzaci in Serbia. This research was carried out by observation on 15 permanently labeled lower branches, every 6-9 days. Growing of insects in order to determine fertility and fecundity of females, the duration of developmental stages and the amount of food consumed by larvae and adults was carried out in a building with outdoor conditions. Results are showing that overwintered adults become active from the beginning of the second decade of March until beginning of April, female fertility was ranged from 30 to 104 eggs, and total fecundity from 58 to 109 eggs. Embryonic development was in range from 9 to 11 days. First larvae were found on leaves in the second decade of April, and the last are observed at the end of June. Ash weevil larvae undergo three larval stages, The entire larval stage development lasts 16-20 days. Larvae consumed average 3.3 cm2 of narrow - leaved ash leaves. Pupal stage lasts from 6 to 8 days. Adults of new generation occur in the same year from the beginning of the second decade of May to the beginning of July, and immediately after eclosion starts with additional feeding for overwintering and each adult feeds on average 2.5 cm2 of narrow leaved ash leaves.