Biology and bionomics in Scotland of Anthocoris gallarum‐ulmi

. 1. Observations were made on the biology of Anthocoris gallarumulmi De Geer (Hemiptera ‐ Heteroptera: Anthocoridae) in West Central Scotland from 1973 until 1975. The life cycle was intimately linked with those of its principal prey species Schizoneura ulmi and S.patchae , leaf roll‐gall aphids, and elm, their primary host ( Ulmus sp.). 2. Overwintered adults emerged in late April/May and could be found on a number of early flowering tree species, before congregating on elm in late May/June. This population was univoltine and exhibited obligatory female reproductive diapause. 3. Overwintered females emerged already mated but the subsequent pre‐oviposition period was 25 days and oviposition period 27 days. Ova were deposited only in close association with galls of S.ulmi and Spatchae , and behavioural variations were shown between sites. Fecundity was c . 16 ova per female. 4. The incubation period was c . 8 days with the subsequent period of larval development 38–53 days, during which time the diet was almost exclusively either S.ulmi or S.patchae . Intergall migration was characteristic of post second instar larvae, which resulted in the concentration of fifth instar larvae and adults in a limited number of galls. It was during this period of local high population density that mating occurred. 5. Adults left elm within 14 days of imaginal ecdysis and thereafter, until overwintering, were recorded in only very low numbers from a range of tree, shrub and herb species. 6. Overwintering adults selected as hibernacula the bark of four tree species but principally Acer pseudoplatanus and Quercus robor . Females required a period of at least 75 days of cold ‘shock’ to terminate reproductive diapause. 7. Mortality among males surviving to spring emergence was 67%.