The involvement of the endocrine system in courtship, mating, maternal behaviour and the gonadotrophic cycle was studied in the earwig, Eubnrellia annulipes, after application of JH 111 and, alternatively, precocene 11.Topical application of 35 or 122 pg of JH 111 to newly eclosed females advanced the onset of courtship behaviour from 6.6 f 1.3 days in acetone-treated controls to 1.4 f 2.8 and 0.5 k 2.5 days, respectively. Application of 6 pg of JH I11 had no effect on the onset of courtship behaviour. Applications of Juvenile Hormone had no significant effect on the age at first mating nor on the duration of mating, though the trend is towards advanced onset. The age at first oviposition was advanced by hormone treatment; clutch size and the proportion of offspring hatching was reduced by hormone treatment. The interclutch interval, size and proportion hatching of the second clutch were not affected by hormone treatment. Topical application of 50 pg of JH I11 to females on the day of oviposition shortened the total duration of maternal care from 15.4 f 0.5 to 5.3 f 1.7 days; whereas in acetone-treated and precocene 11-treated groups maternal care lasted 16.1 f 1.9 and 13.8 f 1.6 days, respectively. The duration of maternal care was positively correlated with number of offspring hatching and fledging.In a corollary experiment, topical application of JH 111 significantly enhanced the onset of the second gonadotrophic cycle as assessed by basal follicle length; application of 20 pg of precocene 11, either singly or in repeated doses, did not delay growth of basal follicles. Finally, repeated application of as much as 80 pg of precocene I1 had no effect on basal follicle length, nor on ovary wet weights.These results are consistent with the hypothesis that intermediate to high titres of JH are associated with oocyte growth, mating, and the cessation of maternal care; low titres of JH appear to be associated with the period of maternal behaviour and slow ovarian follicle development.