43 



grasshoppers being only the various stages of certain leaf hoppers 

 — by far the commonest species being the unfriendly leaf hopper 

 J^assus inimicus. 



As has so frequently been the case when our indigenous locusts 

 have become destructively numerous, many people mistook them 

 for the Rocky Mountain locust, and were unnecessarily alarmed 

 concerning future attacks by this frightfully destructive pest. It 

 seems useless to reiterate what has so frequently been said on this 

 subject— that the Rocky Mountain locust has never, and in all 

 human probability can never, become injurious in Illinois. 



CONCLUSIONS. 



The following general considerations bearing upon the subject of 

 ihe destructive outbreaks of our indigenous locusts, and of the possi- 

 bility of forecasting the future in any given locality where these 

 insects are numerous, are mainly the result of the investigations re- 

 •corded above. Of course no definite rules can be laid down by which 

 predictions can be made. We can only indicate some of the fac- 

 tors to be taken into account in estimating the ratio of probabil- 

 ity. In all cases the entomologist must carefully survey the field, 

 and use his own judgment as to the importance due to each fac- 

 tor of the problem. 



Besides the arthropodous animals mentioned belo;^v, various other 

 agencies — such as the weather, epidemics of contagious diseases, 

 •etc.— must at times be taken into account. 



1. Destructive outbreaks of our common locusts are liable to 

 occur in restricted localities at varying intervals, whenever the 

 •climatic and other conditions favor their development. 



2. There will generally be a gradual increase in the numbers 

 of the locusts for a series of years, until the culmination is reached,^ 

 after which there may be expected a great and sudden decrease. 



3. The great majority of the eggs are deposited in grass lands, 

 — especially in pastures and along roadsides, — and these situations 

 should be examined for the eggs. Here, also, the young locusts 

 will appear at a time when they are most easily destroyed by 

 artificial means. 



4. As a concomitant of this locust increase, there will usually 

 be an increase of the Artli^poda which prey upon the locusts or 

 their eggs; and it is generally owing to the fact that these enemies 

 get the start of the locusts that the outbreak is checked. 



5. Among the more important of these locust enemies which 

 should be observed, and reckoned upon in prognosticating, are 

 the following: 



a. The red locust mite ( Trombidium locustarum), which, when 

 voung, attaches itself to the locusts and sucks their juices; and 

 later attacks their eggs. 



