INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 323 



familiar arc usually dark, with transverse yellow bands across the abdo- 

 men. They are very swift fliers and are often mistaken for bees or 

 wasps. 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 numerous and are called ' ' sweat flies ' ' in 

 the Eastern States. They deposit their rather long, whitish eggs singly 

 upon leaves and twigs which are infested with plant lice, and these give 

 rise to the green larvae. 



There are many groups with entirely different food habits. Some 

 are destructive to plant life, while most are of no particular economic 

 importance. 



While some of these flies do much to prevent the spread of plant 

 lice, they are in turn preyed upon by other insects. Ants, which foster 

 and protect the plant lice, kill and carry off the syrphid larva' in large 

 numbers and greatly reduce their efficiency. 



There are many other enemies, which also prey upon all stages of the 

 syrphid flies. The larva? and pupae are heavily parasitized by internal 

 hymenopterous parasites, especially of the genus Anomalon, 23 * includ- 

 ing, in this State, A. syrphicola Ashm., A. orbitalis Ashm., A. xanthopsis 

 Ashm., and A. maculifrons Cr. The adults are often attacked by a 

 fungus (Empusa sp.), which kills great numbers of them. 



There are many common species in California and it is impossible to 

 include all here, so only a few representative destructive and beneficial 

 forms are given. 



THE OBLIQUE SYRPHID FLY 

 Allograpta obliqua Say 



(Fig. 316) 



Description. — This is one of the smaller syrphid flics, being seldom 

 over | inch long. The body is slender ; eyes, dark red ; face, yellow 

 with dark median line; antennae, amber-brown; thorax, iridescent 

 green ; scutellum and legs, light yellow ; 

 abdomen, dark with four transverse yellow 

 bands on the dorsum, and yellow longi- 

 tudinal markings at the base of the amber 

 or dark brow r n abdominal tip. 



Distribution.— This is one of the most 

 widely distributed and common species Fig. 31c— The'obiique syrphid 



found in the southern nart of the State fly - Allograpta obliqua Say. Rn- 

 luuuu m me souuitiii pan 01 liil oiaie, larged five times. (Author's illus- 



bemg present in practically every locality, tratiqn, p. c. Jr. Ent.) 



It is rare in the central and northern sections, as noted by W. M. 



Davidson. 



Hosts.— The larva? of this fly work upon a great number of lice, and 

 adults have been reared from those feeding upon the oat aphis, Aphis 

 avencB Fab., the black citrus plant louse, Toxoptera <ti<r<uilta Koch, the 

 melon aphis, Aphis gossypii Glover, and the destructive pea aphis, 

 Macrosiphum pisi (Kalt.). 



- 2 Hnseet Life, III, p. 460, 1891. 



