Status of Black-Headed and Red-Headed Types of Hyphantria cunea (DRURY) (Lepidoptera : Arctiidae) : I. Biology of Two Types and Results of Crossing Experiment

The larvae of the red-headed type (OLIVER's orange race) of Hyphantria cunea in Arkansas, U. S. A., make a silken-web which is remarkably different in shape from that of the black-headed type. The former type is considered to be reproductively isolated from the black-headed type by its seasonal life cycle and host preference. Laboratory experiments revealed that (1) the duration of larval and pupal development of the red-headed type reared under constant temperature on artificial diet was longer than that of the black-headed one; (2) the critical photoperiod for the induction of diapause was between 14 and 10 hr; (3) feeding activity of the red-headed larvae was nocturnal while the black-headed larvae fed in the day-time as well as at night; (4) full grown larvae tended to hide behind something under artificial illumination ; and (5) the shape of the web-nest spun by red-headed larvae was greatly different from that of black-headed larvae. Some of the black-headed type collected from the Canadian Maritime Provinces entered diapause at 18 hr photoperiod, suggesting the possible occurrence of an obligatory diapause.The adults of red-headed and black-headed types could easily copulate with each other. Hybrids between red-headed males and black-headed females, having an intermediate larval color, grew at a developmental rate that was similar or somewhat higher than that of the black-headed type. Feeding and web-making behavior of the hybrids was of an intermediate nature between the two parental types. Inbreeding between F1 moths and the back-cross with adults of the two types gave viable larvae.