SWEET POTATO PESTS— SYRPHUS PLIES 



1957 



Sweet Potato WeeYil 



Cylas formicarius Tryon. 



Cylas formicarius is a very widely dis- 

 tributed species, and a native probably 

 of Cochin China. Compere has a record 

 of finding it at Bombay and also at 

 Calcutta in sweet potatoes offered for sale 

 in the public markets at both of those 

 places. It has also been reported from 

 Madagascar, Southern United States, 

 West Indies and Northern Australia; but 

 not yet, so far, from the sweet potato 

 fields or markets of this country. 



It also occurs in the Hawaiian terri- 

 tory. 



The beetle is somewhat ant-like in 

 form. The color of the elytra (wing 

 covers) and of the head and beak is 

 bluish black; that of the pro-thorax is 

 reddish-brown. The yellowish-white oval 

 eggs are laid in small cavities eaten by 

 the parent beetles near the stem end 

 of the tuberous roots. The milk-white 

 larvae bore little tunnels through the 

 roots in all directions, so that the vine 

 dies; and frequently the entire potato is 

 tunneled; these burrows become filled 

 behind the larvsa with excrement. When 

 about to assume the pupa state, the in- 

 sect forms an oval cavity at the end of 

 its burrow, whence it undergoes its trans- 

 formation. 



Tortoise Beetles. See G-oM Bugs^ this 

 section. 



Syrphus Flies 



SyrpMdae 



Flower, Honey or Sweat Flies 



Always among the plant lice are to be 

 found greenish, flat, sticky-looking 

 "worms" which are decidedly pointed at 

 one end and do not have distinct head, 

 eyes or legs. These so-called "worms" 

 are the larvse or maggots of flies be- 

 longing to the family ByrpMdae, which 

 are commonly called syrphid or flower- 

 flies. The larvae vary from the minutest 

 firstrhatched maggot to nearly an inch in 

 length, according to the species to which 

 they belong. They are usually light or 



dark green, but some may be brown, 

 orange, very light or nearly black. Those 

 feeding upon plant lice are green with a 

 longitudinal darker green or brownish 

 stripe on the dorsum. The mouth is 

 situated at the small end and all of the 

 food is obtained by puncturing the body 

 walls of the lice and then sucking out the 

 contents. This operation is easily ob- 

 served in the field. The maggot firmly 

 supports itself by the large posterior end, 

 raises itself up and begins to blindly 

 move its mouth end about in quest of 

 food. If it touches a plant louse it im- 

 mediately lifts it into the air and sucks it 

 dry. This is very rapidly repeated, with 

 very disastrous results to the lice. When 

 the larva is full grown it seeks some 

 sheltered spot in which to pupate (trans- 

 form into the adult fly) . This it may do 

 on the stems or upon the surface of a leaf. 

 The puparium is a long, roundish, or 

 oval, brown body, showing no signs of 

 life. The adult fly removes one end of 

 the case to escape. The adults are usual- 

 ly dark with transverse yellow bands 

 across the abdomen. They are very swift 

 fliers and are often mistaken for bees. 

 They are common around flowers, feeding 

 upon the nectar and from this habit get 

 the names "flower or honey flies." On 

 hot days they are sometimes very num- 

 erous and are called "sweat flies" in the 

 Eastern states. They deposit their eggs 

 singly upon leaves and twigs which are 

 infested with plant lice and these give 

 rise to the green larvae. 



While these insects do much to pre- 

 vent the spread of the plant lice, they 

 are in turn preyed upon by other insects. 

 Ants, which foster and protect the plant 

 lice, kill and carry off the larvae in large 

 numbers and greatly reduce their eflaci- 

 ency. Internal parasites also prey upon 

 them. 



There are three species which are do- 

 ing good work in keeping down plant lice; 

 a very large species, LasiophthicMS pyra- 

 stri Linn., the American syrphid, Syr" 

 pfius amerieanus Wied., and the small spe- 

 cies AlJograpta oUiqua Say. 



