October, '21] freeborn: anopheles occidentalis 419 



respect to temperature, humidity, breeding places, and food but death 

 always resulted with one exception before the third deposition and 

 subsequent dissection invariably showed the ovaries filled with eggs 

 which from a biological standpoint would indicate a premature death.' 

 The total number of eggs that can be deposited by a single female of 

 this first generation under natural conditions must remain a conjecture 

 at this time. Under laboratorj^ conditions the greatest nimiber of 

 separate layings for A. occidentalis was three, with a total deposition of 

 four hundred and ninety -one eggs. 



With this propensity for egg laying in mind which under natural 

 conditions is continued thru an unknown number of batches, the ascend- 

 ing cun^e beginning in late July and reaching its peak in late September 

 is easily foreseen. 



The origin of the over\vintering females is a difficult point to fix. How- 

 ever, Mitzm.ain has shown that engorged females are unable to pass the 

 winter successfully. It is to be inferred therefore, that they are the 

 m-cmbers of the last batch "of the season which occurs if we refer to the 

 chart of male collections and estim.ate the life of the m.ale occidentalis at 

 a week, about the fifteenth of November. Whether these individuals 

 are technically stragglers of the second generation represented by the 

 September peak or of a third or fourth generation is at present unknown. 



The practical points from, a control standpoint in these studies resolve 

 them,selves about the time for offensive measures against malarial mos- 

 quitoes. After the m.igratory flight of the overwintering females there 

 follows a rapid decrease in the adult population to the point when prac- 

 tically every living member of the species is in the aquatic larval stage, 

 (early April in the locality represented in the charts.) The drainage, 

 filling or oiling of all breeding places at this period, if carefully done 

 controls, with the exception of the subsequent breeding of foreign in- 

 vading females, the entire generation that are the progenitors of the 

 summer and fall broods. If this opportunity is neglected, the emerging 

 females capable of depositing many consecutive batches of eggs lay the 

 foundation for an overlapping series of adults and larvae that ensure the 

 survival of the species over a continued campaign directed against the 

 larvae. 



Once again during the year man is given his chance to strike a decisive 

 blow against t!iis species. This opportunity comes in California in Oc- 

 tober or in any locality where hibernation occurs soon after the fall peak 

 of the adult population takes place. At this time, the number of 

 adults are being rapidly depleted but breeding waters are stocked with 

 larvae which will give rise to thousands of females emerging too late to 



I 



