SEASONAL OCCURRENCE OF LYGUS BUGS ON FIELD CROPS IN FINLAND

A long term survey of Lygus populations (Heteroptera, Miridae) was car ried out on eight arable crops in southern Finland. Sweep net samples were taken weekly during the growing season in 16 successive years. Th e hibernated adults first appeared in May on overwintered crops: winte r rye, red clover-timothy ley and winter turnip rape. Turnip rape and ley harbored the most Lygus adults until the end of June even if some of them started to move to spring cereals (wheat, oats and barley), po tato and sugarbeet after the emergence of these plants. The numbers of adults on cereals remained small until the crops reached the heading stage. The peak occurred in the first half of August. The adult number s on potato and sugarbeet were also highest in August. The total numbe r of adults was highest on wheat. Nymphs were found on all the studied crops. They were first captured in the second half of June and reache d a peak between mid-July and mid-August. Numbers were highest on whea t. The most common species on all crops was L. rugulipennis Poppius, c onstituting 92% of the adults. The other Lygus species were L. gemella tus (Herrich-Schaeffer), L. pratensis (L.) and L. punctatus (Zetterste dt). A few specimens of L. wagneri Remane were also found.