VARIATIONS IN THE TENDENCY TO DIAPAUSE AMONG SUCCESSIVE GENERATIONS OF LABORATORY STRAINS OF TRICHOGRAMMA SPECIES (HYMENOPTERA, TRICHOGRAMMATIDAE): ENDOGENOUS OR EXOGENOUS?

摘要

Variations in the tendency to diapause among successive generations of laboratory strains reared under constant conditions were reported for many insects and mites. However, as far as it is known, the relative importance of the endogenous and exogenous components of this variability has not been investigated experimentally. A study with 12 successive generations of laboratory strains of Trichogramma telengai Sot and T principium Sug. et Sor was carried out. A total of 12 strains originated from different females and/or reared under different photo-thermal conditions (at 20 and 25 degrees C and day length of 12 and 18 h) were investigated. The tendency to diapause was estimated by the proportion of the progeny, which diapaused at temperatures of 13, 14 and 15 degrees C. Although the variations in the tendency to diapause in sequential generations of different strains of the same species were positively correlated, the correlation between different species was also very strong suggesting that endogenous (species-specific) factors are not the main reason for the observed changes. The data obtained for different photo-thermal conditions of incubation of the studied strains and of their progeny also correlated suggesting that occasional changes in temperature or day length are not the reason for the changes in the proportion of diapausing progeny Evidently, the differences in the tendency to diapause among generations of the studied Trichogramma species were caused mainly by some uncontrolled environmental factors. This in no way excludes the possible role of the endogenous processes, but suggests the necessity for a critical analysis of the available data on the "spontaneous" dynamics in the tendency to diapause among successive generations of laboratory strains of insects and mites.