REPORT OF THE STATE ENTOMOLOGIST T914 79 



with 43 . The available data, so far as the elm leaf beetle and local 

 conditions are concerned, justify the following tentative conclusions: 



The inhibitory action of low temperatures is about equally evident 

 in both maximum and minimum temperatures when 43 ° or 55 are 

 taken as zero The contrast is much more apparent in effective 

 temperatures when calculations are based on 55 , and then the 

 difference from the average approximates the sum of similarly 

 obtained maximum and minimum units. 



A reduction below the average of 30 to 40 units in either maximum 

 or minimum temperatures or of 70 units in effective temperatures 

 (if 55 is taken as o) during a ten-day period when egg laying by the 

 elm leaf beetle is normally at its height, checks oviposition and is 

 very likely to be followed by an unusual mortality in both eggs and 

 young grubs. 



The relation existing between the development of the insect and 

 the effect unusually low temperatures may have, should be always 

 kept in mind, since if this is done we may be able to explain in part 

 why the elm leaf beetle may be abundant and injurious in some 

 sections and almost innocuous in others the same season, due to the 

 fact that a widespread, cool wave would not have a uniform effect 

 upon the insect, owing to its development being materially affected 

 by local influences. Studies of other workers have shown that under 

 normal conditions the rate of average variation for the beginning or 

 ending of any biological phenomenon is not far from one day for 

 every fourth of a degree of latitude or for every 100 feet of elevation. 

 With this as a basis and the preceding regarding temperature in mind, 

 it may be readily seen that a cool period might be very injurious to 

 the elm leaf beetle at Nassau and comparatively harmless in the 

 lower Hudson valley or on Long Island. 



These facts in relation to temperature have a practical bearing, 

 in that they give an approximate basis, at least, for determining the 

 probability of serious injury locally before the brood has developed 

 to such an extent as to damage the trees materially. It is easy to 

 approximate the number of beetles which have overwintered by the 

 amount of feeding upon the unfolding leaves, and now it seems pos- 

 sible to go further and determine in advance, with some degree of 

 assurance, whether eggs and young grubs will thrive and develop 

 normally, provided we have reasonably detailed information in 

 respect to temperature conditions. 



The calculation of temperature units is not a congenial occupation 

 for the average man and we arc therefore giving below the maximum 

 and minimum temperature records for Chatham, N. Y., for 19 10 to 



