

INSECT ECOLOGY 363 



temperature of 24 F. and below. The northern limit of the San 

 Jose scale insect corresponds approximately with the average annual 

 minimum isotherm of 15 F. This species dies out in central Wis- 

 :onsin and cannot survive in Minnesota. The wide-ranging cotton 

 )ollworm, or corn ear worm, does not winter in Minnesota and no records 

 >f injury occur in Montana, Wyoming or the Dakotas. The harlequin 

 cabbage bug maintains a foothold in the latitude of Long Island, 

 mthern Ohio and southern Illinois, but has been unable to extend 

 its permanent range farther north on account of being killed off by cold 

 during hibernation. 



A blanket of snow may offset the effects of minimum temperatures, 

 as with the striped cucumber beetle, which hibernates in the soil, the 

 codling moth, which passes the winter as a caterpillar in a cocoon under 

 bark, the scale insects, and many other species. 



Occasional periods of extremely low temperature, occurring at 

 long intervals, are temporary checks upon the distribution, but the 

 exact northern limits of distribution depend rather upon the average 

 minimum temperature. 



PRESSURE 



From the few observations that have been made upon the subject it 

 appears that insects are sensitive to variations in atmospheric pressure,, 

 as birds and mammals, including man, are said to be. Atmospheric 

 pressure as correlated with humidity affects animals indirectly through 

 its effects on evaporation. Thus high pressure with low humidity 

 means increased evaporation, and vice versa. 



The following extracts are from an interesting article by D. C. Par- 

 ian on the effect of storm phenomena on insect activity. 



With a rapidly falling barometer several species of flies (Muscidae) 

 first become nervously active and then go into a state of partial coma, 

 in which state they are more subject to the action of other destructive 

 agencies, diseases probably included. The decrease in the number of 

 flies is quite appreciable after a severe tropical storm. 



The adults of the fly Chrysomyia macellaria apparently will not chill 

 and die under the effect of a rising barometer as under a lowering baro- 

 metric pressure. 



Insects attracted to lights are more active during high barometric 

 periods and especially while the barometer is rising. 



Bred adult Diptera tend to emerge on periods of rising barometer. 



