454 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



ECONOMIC SYRPHIDiE IN CALIFORNIA^ 



By W. M. Davidson, Scientific Assistant, U. S. Bureau of Entomology, Docidous 

 Fruit Insect Investigations 



The Syrphickc have long been looked upon as an important factor 

 in the control of plant-lice and other homopterous insects, and although 

 there are a few species injurious to cultivated plants our present knowl- 

 edge plainly indicates that the balance is very heavy on the beneficial 

 side. 



California is rich in beneficial species, the majority of which belong 

 lo the tribe Syrphini which is centered around the type genus Syrphus. 

 These species prey almost exclusively on plant-lice, the species Baccha 

 lemur Osten Sacken attacking mealy-bugs iPseudococcus) and Sphcv- 

 rophoria sulphuripes Thomson being predaceous on the Bean Thrips 

 (Heiiothrips fasciatus Perg.) in southern California. 



Just as we have imported from Europe many injurious aphidids, e. g., 

 Aphis pomi DeGeer, on apple, pear, loquat; Hyalopterus arundiyiis 

 Fabr., on prune and plum; Aphis rumicis L., on bean; Aphis medi- 

 caginis Koch on leguminous crops; Macrosiphum pisi Kalt., on peas; 

 Aphis hrassic(v L., on cruciferous crops; Chromaphis juglandicola 

 Kalt., on walnuts, so there have come to us some of their syrphid 

 enemies. By far the most important of these is Catabomha pyrasfri 

 L. This species finds a home throughout California and in certain 

 years becomes extremely abundant wherever severe aphidid infesta- 

 tions occur in orchard or field. Two such years in central California 

 were 1912 and 1914. The adult fly is easily recognizable by its large 

 size and by the three pairs of lunate whitish-yellow spots on the ab- 

 dominal disc. A melanoid variety of the female (unicolor) is spotless 

 and this form is rare except in years when the species is especially 

 abundant. In 1914 the variety was very abundant while in 1913 and 

 1915 very few could be observed. The pale green, white-striped larvee 

 are voracious feedeis. They may consume a thousand plant-lice of 

 average size in the course of their two or three weeks' larval existence. 

 They appear first early in March and thus have a start of the lady- 

 bird beetles and other predators which do not appear much before 

 April. About the first of March the adult flies begin ovipositing among 

 colonies of winter-feeding plant-lice such as Macrosiphum rosiv L. on 

 roses and Macrosiphum solanifolii Ashm. on weeds such as filaree 

 (Erodium) and toward the end of the month eggs are placed among 

 young colonies of orchard aphidids the stem-mothers of which hatched 

 from the winter eggs in February and early March. It is not common 



1 Published with the permission of the Chief of the Bureau of Entomology. 



