424 KEPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 

 EFFECT OF THE WEATHER ON THE YOUNG LOCUSTS. 



That the young locusts thrive best and are healthiest during dry 

 springs and summers, is not only what we should naturally conclude 

 from what we know of the climatic character of the permanent habitat 

 of the insect, but it is proved by experience. Excessive moisture, 

 especially when accompanied with cold, is prejudicial to them. They 

 can stand a slight frost with impunity, but 15^ below freezing-point 

 usually kills them. ' 



EFFECT OF THE WEATHER ON THE EGGS. 



While a knowledge of the influence of the weather on the young locusts 

 can have no especial practical bearing, since we can never know before- 

 hand the kind of weather we are to have, it is quite different in regard 

 to the eggs. There is a possibility that by knowing the conditions most 

 favorable or most unfavorable to the eggs, and the thermal constant 

 required to properly hatch them, we may be able to anticipate results. 

 It is evident that if the amount of heat which the locust-egg has re- 

 ceived is the principal factor in determining its development, we ought, 

 having once determined this thermal constant, and having a series of 

 daily observations of the temperature of the earth in which the egg 

 lies, to be able to state on any day in the early spring just how near the 

 egg is to hatching; and this information would, it is conceived, fre- 

 quently be of use to the farmer, since he would know then whether it 

 would be safe to plant or best to delay. For instance, if in Missouri, 

 by April 1st, the eggs are within two days of hatching, and the 

 weather indications of the Signal Office predict continued warm or very 

 warm weather, we may anticipate that the eggs will surely hatch in a 

 few days, and that succeeding cold spells and rain will kill off the 

 early young locusts. 



Of course such predictions will have only special and local value, and 

 for their success must depend on the accuracy of our knowledge of 

 (1) the temperature of the soil, and (2) the thermal constant or total 

 amount of heat required to hatch the locust-egg. The chemical effects 

 of solar radiation we believe to be of minor importance, since the solar 

 rays that penetrate into the soil belong to the red end of the spectrum. 



In a broad way we know, from the sub-boreal nature of the insect, 

 that its eggs will stand intense cold, for they are normally laid where 

 the winters are long and intense. We may therefore assume that a 

 severe and steady winter in the Temporary region will better preserve 

 them and cause them to hatch more regularly in spring than a mild and 

 changeable winter ; and the history of the winter of 1874-'75, compared 

 with that of 1876-'77, bears out the assumption. In other words, the 

 more nearly the winter of the Temporary region approaches in character 

 that of the Permanent region, the better will the eggs be preserved; and 

 the rehitive mildness of the winter in the more southern latitudes — the 

 alternate freezing and thawing, and corresponding check and stimulus 



