June, ’IS] 
BURGER AND SWAIN: WALNUT APHIS, FUNGUS 
281 
Insect Enemies 
Insect enemies of the walnut aphis, particularly the predaceous 
enemies, are a very important factor in their control. Observations 
by the writers showed that these were present everywhere, in some 
cases being very abundant and apparently accomplishing a great re¬ 
duction in the aphid infestations. Among the more common enemies 
may be mentioned the ashy gray ladybird beetle ( Olla abdominalis 
Say). About the middle of May the eggs of this species were abundant 
in the vicinity of Santa Paula, El Monte, Walnut and Tustin. By the 
latter part of the month, the larvae were present and feeding extensively 
on the aphids. These pupated in early June and the adults appeared 
shortly before the extreme heat. On the San Joaquin Fruit Com¬ 
pany’s groves, these were very abundant. 
Another common predaceous enemy was Hippodamia convergens 
Guerin, the larvae and adults of which were present from May to Sep¬ 
tember in all groves examined by the writers. The third in abundance 
was the green lace wing ( Chrysopa californica Coquillet), which was 
very plentiful in May and June in Ventura, Los Angeles and Orange 
Counties. From time to time larvae of various syrphid flies, particu¬ 
larly Catabomba pyrastri (Linnaeus), were noted, although never in 
any great numbers. Occasionally larvae of Sympherobius angustus 
(Banks) were found, and in the vicinity of Walnut and Spadra, Los 
Angeles County, adults and larvae of Scymnus sp. were observed. The 
inclination is to give predaceous enemies credit for any reduction of 
aphids not proven to be directly attributed to other agencies, as for 
instance the heat and fungus parasites. 
Reinfestation of Groves 
/ 
About six weeks after the hot weather mentioned above, an examina- 
tion of the walnut groves of the San Joaquin Fruit Company was 
made. The aphids were still very scarce. A count of 186 leaves 
gave an average of 6.54=1=0.30 aphids per leaf, showing that as yet they 
had not been able to reestablish themselves to any great extent. By 
September 12, three months after the excessive heat, a count was 
again made, 50 leaves showing an average of but 12.02=1=1.39 aphids 
per leaf. In that vicinity, however, the summer had been dry and 
warm, which together with the predaceous enemies had kept the in¬ 
festation down. Table 3 gives the results of a count made on the 
Cogswell groves, El Monte, on September 12. 
