none Lygocoris pabulinus can be reared continuously on potted potato plants when the light period is at least 17 h. Minimum generation time, including a premating period of 6 days, is approximately 40 days at 20 degree C. Young females lay up to six eggs/day and 3-4 young nymphs per female are produced. Individual females lay up to 200 eggs and mating once is sufficient to maintain maximum egg production for at least 2 weeks. While detached shoot tips of herbaceous plants like potato also are adequate food sources for nymphs and adults, similar tips of apple, pear, currant, raspberry and rose are not. Attempts to rear L. pabulinus on apple seedlings also failed. This explains why many older nymphs arising from overwintered eggs already leave the apple trees: to complete their development on herbaceous host plants. Long light periods induce the summer generation adults to stay on these hosts. Light periods of 16.5 h or less during juvenile development induce females, usually of the second generation, to oviposit on woody shoots like apple and Forsythia, but these females still require herbaceous plants for feeding. A partial third generation sometimes occurs after a warm spring and summer. These observations appear to explain host-plant alteration in L. pabulinus. Experiments showed that most damage to fruits is caused by nymphs older than second instar. The time to monitor this instar is estimated best when the daily temperature sums above 4 degree C accumulated from 1 January amount to 568-2.05*D -Ts245 degree days where D -Ts245 indicates the number of day on which 245 degree days is reached. A few parasitoid Peristenus laeviventris (Ruthe) (Braconidae, Euphorinae) were reared from full grown nymphs in spring, and epizootics of Entomophthora sp. were seen in 3 years out of 10. What causes the great numerical variation of L. pabulinus in apple orchards over the years is still unknown.