16 MONTANA EXPERIMENT STATION BULLETIN 474 



was reported in gardens and ornamental shrubbery plantings from 

 nearly all parts of the state. Two pounds of DDT per acre as a 

 spray is apparently satisfactory for controlling these insects; how- 

 ever, the problem of residual protection against new bands of 

 blister beetles moving into the sprayed fields has not been satis- 

 factorily worked out. 



FLEA BEETLES (Epitrix sp. and Systena hlanda) 



The potato flea beetle (Epitrix sp.j has always been a problem 

 to Montana farmers and gardeners when raising cruciferous veget- 

 ables. It has also been an economic factor in sugar beet production 

 during the past two years in some parts of Montana. In the Milk 

 River Valley, the Great Falls area, and the Triangle Area where 

 sugar beets are produced, adult potato flea beetles attacked a large 

 percentage of sugar beet fields when the seedling beets were in the 

 early two-leaf stage. This occurred in both 1949 and 1950. In 

 most cases, the beetle attack was severe enough to necessitate 

 replanting or abandoning the field. This condition also existed 

 in the Yellowstone Valley in the Billings area where in addition 

 to adult flea beetle damage, larvae presumably of the same species 

 were found feeding on the seedling hypocotyl. These larvae were 

 not found in the northern area. Damage to the seedling hypocotyl 

 did occur m the northern area; this damage was attributed to 

 adult beetles feeding down in the cracks of the soil on cool days. 

 It should be noted that the potato flea beetle populations in all 

 cases were comparatively low, averaging less than one beetle per 

 row foot; however, it was apparent that these low beetle popula- 

 tions could inflict severe damage to sugar beet seedlings in their 

 earlier stages of growth. Applications of 5% DDT dust at rates 

 varying from 12 to 20 pounds per acre gave protection from 

 potato flea beetles varying from verj^ good to practically no pro- 

 tection. 



The two-striped flea beetle (Systena hlanda) occurred occa- 

 sionally in sugar beet fields in both the Milk River and Yellowstone 

 valleys. This flea beetle was a consistent economic problem. 



THISTLE BUTTERFLY CATERPILLARS (Vanessa cardui) 



The larval form of the painted lady butterfly was quite pre- 

 valent throughout most of the state in 1949. For the most part, its 

 feeding activities were confined to the perennial weed, Canada 

 thistle. Only two cases of crop damage were reported — one in 

 potatoes and the other in beans. One army-like movement from 

 a defoliated Canada thistle patch through a barley field was ob- 

 served. In this case, only the Canada thistles in the barley field 

 were attacked. The barley was not touched. No thistle butterfly 

 caterpillars were found or reported in 1950. 



