INSECTS INJURIOUS TO MELONS, CUCUMBERS, ETC. 347 



ladybird-beetles and their larvae, of which the convergent lady- 

 bird,* the nine-spotted ladybird, f and the spotted ladybird, J 

 shown in Figs 1-5, are among the most effective, and the maggots 

 of various common syrphus-flies, and the aphis-lions. Even 

 more beneficial are the little parasitic flies whose larvae live within 

 the maggots and destroy myriads of them with incredible swift- 

 ness. The most common of these 1f are the same as the most 

 common parasite of the green bug (Fig 120), and they often destroy 

 the aphids over a whole field in a few days. They are most effect- 

 ive in bright, warm weather, when they reproduce most rapidly, 

 but in cool, moist weather they reproduce but slowly, and if such 

 a summer follows similar weather conditions during the spring, the 

 aphids multiply rapidly without a corresponding increase of their 

 enemies and serious damage results. Inasmuch as these same 

 enemies attack the cabbage-aphis, Professor C. E. Sanborn* has 

 suggested that the cabbage-aphis might be encouraged to multiply 

 on crops planted near melons or cucumbers, so that an abundance 

 of parasites and insect enemies might be in readiness to attack the 

 melon-aphis when it appears. This might be done by planting 

 kale, rape, or wild mustard in the fall, upon which the cabbage- 

 aphids will pass the winter and will multiply in early spring. 

 This trap crop should be planted in rows around the prospective 

 melon-field, and if the latter be large, rows should be planted 

 through it. If the kale does not soon become infested with the 

 cabbage^aphis, transport some from the nearest cabbage-patch. 

 The ladybirds and parasites multiply rapidly with plenty of the 

 cabbage-aphids for food, and as soon as the food supply becomes 

 scarce they are forced to migrate and will search out any colonies 

 of melon-aphids. This method has not come into general use. 



Control. The most important factor in the control of this, 

 as well as many other aphids, is constant watchfulness, inspect- 

 ing the plants frequently and destroying badly infested individual 

 plants and treating small areas before the pest becomes spread 

 throughout the crop. 



* Hippodamia convergens Guer. 

 t Coccinella 9-notata Herbst. 



J Megilla maculata DeG. Family CoccinellidcB. 



Family Chrysopidce. 



^ Lysiphlebus testaceipes Cress. Family Braconidce. 



* See Bulletin 89, Texas Agr. Exp. Sta., p. 44. 



