Lawson, Chamberlin, and York (1951) showed that flights of the beet leafhopper 

 ceased at temperatures close to 58° F. This leafhopper is normally regarded as a day- 

 time flier, but on hot nights when the temperature was 70° near midnight, large numbers 

 came into light traps at the laboratory, Modesto, Calif. On such nights other day-flying 

 insects such as grasshoppers and butterflies were also captured. Rockwood has also 

 recorded night flights of diurnal insects under similar conditions. 



To obtain some fresh data on the effects of temperature on the flight of noctuid 

 moths to lights, the writer took records for 5 years from a stationary ultraviolet light 

 trap (20-watt fluorescent BL bulb) at the laboratory, Walla Walla, Wash. To smooth out 

 the large seasonal variations a 5-day running average was used and the daily catches 

 computed as percentages of that average. The midnight temperature reading from a 

 thermograph about 100 yards away, in a standard shelter, was used. Tabulating these 

 catches against the midnight temperatures, the index catch increased from 62 percent 

 between 36° and 45° F. to over 103 percent between 56° and 65°, with a decrease at 

 higher temperatures. This would indicate a rather low temperature optimum for noctuid 

 flight. 



Because of the effects of slight changes in temperature on flight observed in the 

 field, a further tabulation was made in which the index catches were tabulated against 

 the change in temperature from the preceding night (midnight temperatures). No statis- 

 tical analysis has been made, but about 500 nights were included in the tabulation, and 

 all points between -14° and 12° are based on 10 or more nights. A freehand line drawn 

 through the averages for 2° intervals indicates a change of somewhat more than 2 per- 

 cent in the catch for each change of 1° in midnight temperature. 



In making the above tabulation it appeared that a second night of increasing or de- 

 creasing temperature had less effect on the catch than the first night. This might indi- 

 cate, for rising temperature, the possible attrition of the supply of photosensitive moths 

 from the first warm night. Causes might be local population shifts or changes in the rate 

 of emergence from the pupal stage. The same records indicate that very hot nights were 

 unfavorable for noctuid flight, but the traps captured large numbers of midges, caddis 

 flies, small beetles, and leafhopper s. 



HUMIDITY. Stirrett (1938) showed that 89 percent of the moths of the European 

 corn borer flew at saturation deficits between and 6 mm. His data do not indicate, 

 however, whether such nights were customary or rare, but it may be assumed that many 

 such nights occurred in southern Ontario. My own early work in Minnesota and Montana 

 indicated that there might be an optimum humidity for flight. This was between 50 and 54 

 percent in Minnesota and between 30 and 40 percent in Montana, a much drier area. The 

 relationship was not well marked. 



WIND. Stirrett (1938) stated that the flight of the European corn borer was not affected 

 by winds with velocities up to 17 miles per hour. The writer had noted the same for 

 flights of noctuid moths. This is definitely not true of their attraction to light. A wind of 

 10 miles per hour is sufficient to reduce the night's catch to nearly zero. Working with 

 portable light traps, we have seen the catch of noctuids (and most other insects) cease 

 abruptly with the coming up of a wind of 5 to 15 miles per hour. Because a portable 

 anemometer was not used to measure these winds, definite wind data are lacking. How- 

 ever, after giving up trapping because of wind, we have repeatedly seen numbers of 

 moths still flying around, and found them feeding at flowers. 



The general conclusion regarding wind is that it does not influence moth flight 

 greatly if other conditions are favorable, but that it practically inhibits their coming to 

 lights. 



ATMOSPHERIC PRESSURE. This apparently has little effect on either flight or 

 photosensitivity. References in the literature largely refer to conditions before a storm. 

 Here temperature, humidity, andwind, as well as pressure, are liable to be well within the 

 optimum range. 



RAINSTORMS. No definite data. Light traps run in sheltered locations in rainy 

 weather appear to capture as many moths as on rainless nights, if other conditions are 

 favorable. Moths often flock to lighted windows on rainy nights. 



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