Implications of selection and hybridization studies on the mode of inheritance of photoperiodically induced developmental diapause in laboratory strains of the lone star tick (Acari: Ixodidae).

Selection of lone star ticks, Amblyomma americanum (L.), that were reared in the laboratory under short-day photoperiods of 10:14 (L:D) h resulted in third generation (F3) diapause versus F3 nondiapause strain replete nymphs having significantly different mean molting times (days from detachment to ecdysis) of 100.9 versus 54.7 d, respectively; whereas, the F7 unselected laboratory control strain had an even smaller, significantly different mean molting time of 49.5 d. Two hybrid crosses of F2 nondiapause male with F2 diapause female ticks and F2 nondiapause female with F2 diapause male ticks yielded intermediate replete nymphal mean molting times of 62.0 and 68.9 d, respectively. All strains retained the ability to develop rapidly under long-day photoperiodic conditions of 14:10 (L:D) h, although F3 nondiapause strain ticks also exhibited reduced fitness, especially when exposed to the long-day stimuli. Analyses of molting times used as phenotypic values indicate that this diapause trait is incompletely dominant, and these and other observations indicate that inheritance of photoperiodically induced prolonged replete nymphal molting times is polygenic in this species.