34 



FARMERS BULLETIN 804. 



Fig. 25. — The coavergent ladybird (Hippodamia 

 convergent), an enemy of orchard aphids : a, 

 Adult; h, pupa; c, larva. Enlarged. (Chit- 

 tenden.) 



portant influence in their control. The combined effect of these sev- , 

 eral factors normally keeps the aphids pretty well reduced, but whenlj 

 for any reason their activities are lessened the aphids may increase' 



enormously and do wide- 

 spread injury. Heavy driv- 

 ing rains are believed to be 

 inimical to aphids, whereas 

 cool, cloudy weather seems 

 to reduce the activities of 

 the parasitic and predacious 

 enemies, permitting the 

 aphids to become corre- 

 spondingh' abundant. 

 Ladybird beetles (fig. 25) 

 may be found in almost any colony of aphids, both the beetles and 

 larvae feeding freely on the insects. Numerous species of these beetles 

 attack the aphids, and they should be protected and encouraged when 

 jiossible. 



Larvai, or maggots, of syrphus flies, also called sweat flies (figs. 26 

 and 27), are very generally present in aphid colonies and are most 

 important checks to their increase. 



The larvae of two or three species of lace- 

 wing flies feed freely on aphids, although they 

 are not so important as the insects mentioned 

 above. 



Probably the most important check to aphid 

 increase, however, is the work of certain minute, 

 four- winged flies which live parasitically on the 

 aphids. These multiply very rapidly and under 

 normal conditions are very effecti^-^e. The 

 bodies of parasitized aphids usually become en- 

 larged, assume a more or less globular shape, 

 and finally show the exit hole of the adult 

 parasite. (Fig. 28.) 



CONTROL MEASURES. 



As previoush^ stated, aphids feed upon plant ^'"- 26.— Larva of the 



, . r 1 , • 1 i! 1 1 syrphid fly AUos/rapta 



juices Avhich they obtain by means or a beak ohngua, an important 

 inserted into the plant tissues. Paris green. enemy of aphids. Much 



, p 1 1 1 XI -1 enlarged. (Metcalf.) 



arsenate or lead, and other arsenicals. or 



stomach poisons, are therefore ineffective against these insects, and 

 the so-called contact spra3's, such as kerosene emulsion, soap washes, 

 nicotine sprays, etc., must be employed.. These sprays, to be effec- 

 tive, must come in contact with the bodies of the insects, and great 

 thoroughness in spraying is necessary. 



