545 



absence of a general outbreak owing to the enormous expense involved, 

 and in the work recorded in this report inspection was confined to 

 localities where the insects were kno\\ai or at least strongly suspected 

 to occur. A table is given shomng the distribution of the pest and 

 the results of the work accomplished from January to May, 1916. In 

 some localities birds alone destroyed many swarms and completed 

 the destruction of others, aided to some extent by parasitic flies. In 

 many other parts birds rendered valuable assistance, but were too 

 few to cope effectively even with the early ajjpearing swarms ; a 

 condition perhaps explainable by the scarcity at this period of surface 

 water at which they might drink. The hatchings in these parts 

 however w^ere most numerous in March and April and by then the 

 birds were migrating to northern Africa or Europe. 



The methods of destruction employed were those developed in 

 former work in South Africa, depending almost entirely on the use 

 of arsenically poisoned syrup, used either to spray the vegetation or 

 in the preparation of a bait to spread among the insects. The syrup, 

 which was issued free of charge, contained to each gallon, about d^ lb. 

 arsenite of soda (80 per cent. As., 0^) and either | gal. of crude treacle 

 or 6f lb. of cheap sugar. Directions for its employment were given 

 at length in a special leaflet. The greatest strength recommended for 

 use either as spray or bait is 1 part of the poison as supplied to 50 

 parts water. In country of the character of that infested in 1915, 

 baiting is generally preferable to spraying ; owing to relative scarcity 

 of water, the favourite basis for bait in this instance was dry horse 

 dung collected in the veld. A warning is issued ^\dth the poison 

 recommending simple precautions against stock-poisoning, bait that 

 is left lying about in heaps being highly dangerous. But little damage 

 of importance due to either hoppers or winged insects has been reported; 

 while the damage that has been prevented is probably incalculable. 

 In the author's opinion, the damage done has probably been about 

 one-tenth of what it would have been without the operations of the 

 previous season, and he is convinced that without the work of 1915- 

 1916, South Africa would have experienced in 1916-1917 by far the 

 most serious locust trouble in its history, the greater extent to which 

 crops are now cultivated rendering a widespread visitation relatively 

 more important than in earlier years. Absolute extermination of 

 locust swarms by artificial measures is impossible ; in such country 

 as was infested in the present invasion a proportion of the swarms 

 are practically certain to escape detection and there are bound to be 

 numerous survivors from the swarms that the average farmer deals 

 with by poison. It is evident that a cycle of years is at present 

 occurring when the locust naturally tends to multiply prodigiously, 

 and it is as yet too early to state with any certainty that it is practi- 

 cable to prevent a great w^ave of the pest from sweeping over the coun- 

 try, but it seems reasonable to suppose that the work already accom- 

 plished has greatly reduced the potential volume of the threatening 

 invasion. It is conjectured that it is largely an increase in bird and 

 insect enemies that causes in time the temporary disappearance of the 

 pest and it is presumed that, while the development of the outbreak 

 is being retarded by methods of destruction, birds and other enemies 

 are increasing. Conditions favourable to the pest doubtless oj^erate 

 in extensive tracts of desert countrv where destruction measures are 



