THIRTIETH REPORT OF THE STATE ENTOMOLOGIST 17 



OTHER IMPORTANT INSECT PESTS, 1943-44 



POTATO INSECTS 



POTATO PSYLLID (Paratrioza cockerelli Sulc) . — To sum- 

 marize the infestations of this pest of potatoes and tomatoes 

 for the seven years that observations have been made, the 

 first recognized outbreak of these insects in Montana occurred 

 in 1938, when it was estimated that the potato crop for the State 

 was reduced by 25 percent, due to its activities. Populations fluc- 

 tuated below the 1938 level with a trend downward until 1943, 

 when no specimens were collected. The survey of that year (made 

 from July 1 to 6 inclusive) embodied 3350 sweeps in potatoes on 

 28 properties in Stillwater, Carbon, Yellowstone, Big Horn, Rose- 

 bud, Custer, Prairie, Dawson, Richland, Valley, Phillips, Blaine, 

 Hill, Chouteau, and Cascade counties. No psyllids were found, nor 

 was there any report later of purple top in potatoes. In 1944 the 

 survey was made from June 24 to 29, and much the same area was 

 covered. Conclusions were drawn from 3200 sweeps in potato fields 

 in Stillwater, Carbon, Yellowstone, Big Horn, Rosebud, Custer, 

 Dawson, Richland, Phillips, Hill, Chouteau, and Cascade counties, 

 and represented samplings from 23 premises. The survey indicated 

 the presence and possible resulting damage in the Yellowstone 

 Valley from Yellowstone to Custer counties. Only slight infesta- 

 tions were present at the time the survey was made in the eastern 

 part of the Triangle area in north-central Montana. 



Some symptoms of the psyllid-caused disease were noted near 

 Hardin on June 24 in Bliss Triumph plantings, and others were 

 reported to this office as the season progressed. 



The long-time viewpoint on psyllid control involves discovery 

 of methods of predicting outbreaks in sufficient time to plan and 

 prepare for control measures. To the south of Montana psyllids 

 are present in damaging numbers sufficiently often that there 

 is justification in recommending the application of control meas- 

 ures every year. In Montana the experience of the last seven 

 years indicates that the opposite is true. Infestations are so spor- 

 adic that it is not economical to recommend annual control, for 

 the cost of this control over a period of years when it might be 

 unnecessary could be greater than the occasional loss sustained. 

 This makes it obvious that the immediate needs for information 

 concerning the potato and tomato psyllid are for methods of 

 prediction. 



The annual survey for this insect serves two purposes. First, 

 it records the fluctuations in psyllid populations. This information 

 is then available for later study and correlation with factors which 



