Interaction of a population of the black‐kneed capsid, Blepharidopterus angulatus , and its prey, the lime aphid

.1 The population dynamics of Blepharidopterus angulatus (Heteroptera: Miridae), preying on the lime aphid, were investigated from 1965 to 1974. Numbers increased or remained stable until 1969, then declined, at least intermittently. K ‐factor analysis showed that the key factor was k 5+6 (loss of adult females, eggs and newly‐hatched nymphs). 2 Detailed study of numbers and mortalities from 1968 to 1971 showed that loss of adult females was the largest part of k 5+6 . Studies of flight activity showed most females probably emigrated from the trees before laying eggs, but k 5+6 was not related to aphid numbers at the time of peak migration. However, variation in k 5+6 depended on the length of time that aphid numbers remained favourable for egg‐laying. 3 Because of the consistently high emigration of adult females, B.anguhtus numbers increased on average by only 10% when aphid numbers favoured egg‐laying. Nett emigration was usually high, probably because the trees were isolated or in rows, with few sources of immigrants to the South‐West (direction of prevailing wind). Since the population declined by 85% in years when aphids favoured egg‐laying for ≤ 20 days, recovery would be slow after a bad year. Since 1969, 1971 and 1973 were all bad years, this explains the intermittent decline in B.angulatus numbers after 1969. 4 Simulation showed that neither increased numbers nor faster population growth of B.angulatus would enhance stability of predator and prey populations, but would lead to over‐exploitation of the latter. Given its low observed rate of increase, it is unlikely that B.angulatus could persist on lime at levels much above those recorded.