Selection for a Non-diapausing Gypsy Moth:1 Some Biological Attributes of a New Laboratory Strain

A non-diapausing strain of the gypsy moth, Lymantria dispar (L.), was selected within 8 generations. Larvae of the 6th generation of this strain (SEL6) and larvae hatched from eggs field-collected in Pennsylvania (PA) were compared with respect to adult morphology, egg mass size, pupal weight, developmental rate, sex ratio, and susceptibility to infection with nuclear polyhedrosis virus (NPV). Apanteles melanoscelus Ratzeburg, a braconid parasite of the gypsy moth, was reared on the non-diapausing SEL strain to determine the rate at which the parasite entered diapause under laboratory conditions. Selection of the non-diapausing strain proceeded under an 18-h daylength, even though the gypsy moth is thought to be photoperiodically neutral. Some SEL8 larvae reared from instar I to adulthood under an 8-h daylength produced egg masses that hatched promptly under the 8 h conditions, indicating that genetic selection has not simply shifted the gypsy moth's critical photophase.