Photoperiodic responses of certain geographical strains of Pectinophora gossypiella (Lepidoptera)

Abstract

Strains of Pectinophora gossypiella were collected from El Paso (32°N) and Port Lavaca (28°N), Texas; Virgin Islands (18°N), West Indies; Villa de Cura (10°N), Venezuela; Palmira (3°N), Colombia; and Saenz Peña (27°S), Argentina. These were reared in laboratory cultures and tested with photoperiods having from 10 to 14 hr of light time/day at temperatures of 21, 27, and 32°C and on a diet having a lipid content of 1 and 5 per cent. The response curves plotted from the combined data obtained in the photoperiods having from 10 to 12 hr of light time/day showed that the incidence of diapause in each strain from highest to lowest was as follows: El Paso, Port Lavaca, Argentina, Virgin Islands, Colombia, Venezuela. Temperature had a profound effect on the incidence of diapause. The higher temperatures strongly inhibited diapause and at 32°C the percentage of larvae of all strains in diapause was very small. An increase in the lipid content of the diet produces a concomitant increase in the incidence of diapause. This was particularly true for the Virgin Islands strain. This strain also showed a strong response to temperature. The critical photoperiod was not affected by temperature or diet. It remained almost the same in the El Paso, Port Lavaca, Argentina, and Virgin Islands strains. The incidence of diapause was always limited in the Venezuela strain regardless of the experimental regimen. In the Colombia strain, a high incidence of diapause was produced only in the photoperiod having a short light fraction of 10 hr. This photoperiod, LD 10 : 14, is never encountered in nature by the Colombia strain. In all strains, diapause was prevented when the light fraction of the photoperiod was increased to more than 13 hr/day.