INJURIOUS TO CUCUMBER, SQUASH AND MELON 137 



producing females — the so-called true sexes — have not been 

 observed. 



The melon aphis is held in check by the attacks of a large 

 series of predaceous and parasitic insect enemies, most im- 

 portant of which are several species of ladybird beetles, syrphus 

 fly larvfe, aphis lions and several species of parasites belonging 

 to the family Braconidse. Under favorable weather conditions, 

 these foes of the melon aphis are able to keep it so well under 

 control that little or no damage is done. In cool, moist weather, 

 however, following a backward spring, the activities of these 

 beneficial insects are retarded and as the aphis is able to breed 

 rapidly under such conditions, the infestation becomes severe 

 and it is not till late in the season that the enemies of the aphis 

 regain their supremacy. Many of these enemies feed on other 

 kinds of aphids having different food plants and it has been 

 suggested by Sanborn that it might be a useful practice to 

 plant cabbage early around fields intended for cucurbits. 

 The cabbage plants soon become infested with the cabbage 

 aphis which furnish food for great numbers of predaceous and 

 parasitic insects. At the first appearance of the melon aphis 

 in the field, they will be on hand in sufficient abundance to 

 hold the pest in check. 



Control. 



The melon aphis usually makes its appearance in a field on 

 isolated vines scattered throughout the patch. It is important 

 that a close watch should be kept in order to locate and destroy 

 these first colonies. Growers sometimes pull up and bury the 

 vines first attacked. While the vines are small, it is possible 

 to kill the aphids by fumigation with tobacco or carbon bisulfid. 

 For this purpose portable covers are used made of oiled cloth 

 stretched over a light wooden frame. The cover is placed 

 over the vine and the tobacco fumes generated by burning 

 strips of paper impregnated with nicotine. In case carbon 



