R. L. Rabb

Physical and physiological factors in diapause initiation of two hyperparasites of the tobacco hornworm, Manduca sexta

Abstract Hypopteromalus tabacum diapauses as a last larval instar and Catolaccus aeneoviridis as a non-pharate pupa within cocoons of the primary parasite, Apanteles congregatus . Four factors (photoperiod, temperature, maternal age, and physiological state of the host) were tested for their significance in diapause initiation of both species. A 10L : 14D photoperiod produced a higher incidence of diapausing individuals than a 13L : 11D photoperiod. In the temperature range from 18 to 24°C, the incidence of diapause was inversely related to temperature. The incidence of progeny entering diapause varied with the age of the mother, younger ones producing fewer diapausing offspring. An increase in the number of C. aeneoviridis entering diapause was observed when the host, A. congregatus , was in the diapausing, rather than the nondiapausing condition. Analysis of the data indicated that interactions between these four factors also played an important role in diapause initiation of both species.

Diapause in the phytoseiid mite, Neoseiulus (T.) fallacis☆

Abstract Female Neoseiulus (Typhlodromus) fallacis exhibited an adult reproductive diapause. Induction of diapause was dependent upon both photoperiod and temperature. The critical photoperiod at 15·6°C occurred between 11·75 and 12·0 hr light/day for a strain collected at Brunswick, New Jersey and reared in the laboratory under long light periods for ca. 2 years prior to testing. When the F 1 progeny of a strain collected at Wilkesboro, North Carolina was reared under a 11·75 hr light/day, 15·6°C regime along with the New Brunswick strain the photoperiodic response of the two strains was similar. Further studies with the New Jersey strain showed that the incidence of diapause at a short light period was averted entirely at 26·7°C. Little difference was shown in the developmental rates of mites under a short and long light period. Diapause duration was reduced at 15·6°C by exposure to a long light period. When held constantly at a short light period, an increase in temperature from 21·1 to 26·7°C reduced the duration of diapause. This reduction may reflect an effect of temperature on diapause termination as well as post-diapause development. Although diapause termination was influenced by both photoperiod and temperature, it occurred eventually under all experimental conditions, including those initiating diapause. There was no significant parental effect on the incidence of diapause in F 1 and F 2 progeny of adults reared under either a short or long light period. However, parental preconditioning did alter diapause intensity. When parents and offspring experienced a short light period, the resulting diapause duration was significantly longer than when parents experienced a long light period and the offspring experienced a short light period.