COMBINATIONS OF CURRENT AND ANTECEDENT CONDITIONS IN RELATION TO WINGPRODUCTION OF APHIDS

¹ From the Zoölogical Laboratory of the University of Michigan

In general, continuous light applied to the strain of aphids here used resulted in more wing-production than did alternating light and darkness, mostly regardless of the other conditions imposed.

More winged offspring were produced at high temperature than at low, in all combinations of other conditions except one. The difference in the one exceptional set of conditions was small.

A mere change of temperature from low to high or from high to low may perhaps reduce wing-production in certain of the combinations of other agents, but not in most of them.

Winged parents produced strikingly fewer winged offspring than did wingless parents if taken from the low temperature stock. Winged parents from the high temperature or alternating temperature stocks produced mostly more winged offspring than did wingless parents, but none of the differences was large.

Winged parents taken from a high temperature stock produced many more winged offspring under all other conditions than did winged parents taken from a low temperature stock.

Wingless parents generally reversed the above response, since they produced more winged offspring if taken from a low temperature stock than if taken from a high temperature, in all combinations of other conditions except one. In that one exception there was no difference between the wingless parents from the two different temperatures.

Regarding the response of parents taken from an alternating stock as compared with constant temperature stocks, no general rule can be stated. The results were very irregular.

Under uniform conditions, and without change from the conditions applied to the parents before their reproductive period begins, there is a rather rapid and steady decline in the number of winged offspring from the beginning to the end of the family. The decline is more rapid for wingless parents than for winged ones.

At high or low temperature and in continuous light the age effect described in the preceding paragraph is the chief factor governing distribution of wing-production through the family.

At high temperature and in alternating light and darkness there is a decline in wing-production early in the family, followed by a sharp rise later, regardless of the type of parents or the temperature from which they were taken.

At low temperature and in alternating light and darkness there is a decline of wing-production early in the family, a slight or moderate rise thereafter, and a decline toward the end of the family, regardless of the type of parents or the temperature from which they were taken.

The most effective of all the agents tested in these experiments is the light conditions (whether continuous or alternating) prevailing during the experiment. Temperature during the experiment is next most important. Wings or winglessness of the parents is third in importance, followed closely by the temperature at which the parents were reared before the experiment began.

The time seems not ripe to attempt a physiological explanation which will fit these results as well as the somewhat divergent ones obtained in previous studies.