63 



The Greenhouse Aleyrodes. 



The immature stages of this insect consist of the egg, three 

 larval stages or instars and a so-called pupal stage. Of these, only 

 the first larval instar is furnished with well developed legs and is able 

 to crawl. The pupal stage is characterized by wax rods of variable 

 length, which arise from the dorsal surface. 



The egg hatches in from ten to twelve days, the larval and pupal 

 stages together last from twenty-five to thirty days, and the adults 

 may live, and as a rule probably do live, for several weeks. 



Adult females are about three times as abundant as the adult 

 males. Unfertilized eggs will hatch, and, as far as known, develop 

 into adults of the male sex. 



An adult female has been known to lay more than one hundred 

 and twenty-nine eggs in thirty-six days. 



There seems to be no reason to doubt that the common green- 

 house Aleyrodes of North America is the same as that described by 

 Westwood in 1856 as Aleyrodes vaporariorum. 



The insect is supposed to have come originally from Mexico or 

 Brazil, but it is at present very widely distributed in greenhouses in 

 Europe and North America. It has a wide range of food plants, in- 

 cluding many of such economic importance as cucumbers and 

 tomatoes. 



The insect is generally believed, by those who have had experi- 

 ence with it, to be the most serious greenhouse pest known at the 

 present day. 



Simple preventive measures may be all that it is necessary to 

 use in many cases to keep the greenhouse free from the insect. 



Spraying tomato plants in greenhouses is to be avoided when 

 possible. 



Hydrocyanic acid gas is the cheapest and most efficient remedy 

 for the Aleyrodes in greenhouses. At present, it is advisable not to 

 exceed the rate of .1 gram of Potassium cyanide per cubic foot of 

 space for three hours' exposure after sunset. Even in a loose house 

 this can be depended on to destroy all the insects except the eggs 

 and a few pupce. Twice this amount of Potassium cyanide per cubic 

 foot of space in a tight house, with the same conditions otherwise, 

 will not injure tomato plants in a reasonable state of vigor, while it 



