HO IF TO COLLECT MOSQUITOES 225 



that tliey could be transported for several hours without 

 injury. They noted also that the large larvae did not 

 withstand the shaking as well as the small ones, but that 

 a sufficient number could always be brought back for 

 studying iDurposes. On expeditions lasting a couple of 

 days they took precaution to remove the corks occasion- 

 ally to give the insects fresh air. White dippers were 

 used, since they could more easily detect the eggs or 

 larvae on the white background, and they found that only 

 rarely could they detect the insects by direct inspection 

 of the surface of the water. 



LarvjTe and pupto, when it is desirable to preserve them 

 in these stages, and it is always desirable to keep a small 

 set of each species, may be kept in vials of alcohol or di- 

 lute formalin (5 to 10 percent.). When preserved in alco- 

 hol they should be j^assed through different strengths, 

 beginning with a weak mixture, in order that they may 

 not shrivel ; or, what is still better, kill the larva) or pupae 

 suddenly in a cyanide bottle, then bring the water nearly 

 to the boiling point in a little porcelain dish over an alco- 

 hol lamp and drop the insects in, leave them until the 

 boiling point is just reached and then remove them. An 

 immersion of only a few moments will suffice. Ordina- 

 rily the larv.To will sink at once to the bottom of the water 

 and very soon thereafter rise to the top. This rising is 

 an indication that the specimen should be removed at 

 once. The specimen may then be preserved in ordinary 

 commercial alcohol and will retain perfectly its color and 

 shape. This method is used successfully with the larvae 

 of many insects. It is not necessary to mount either 



