359 



within the last few years was not suspected of living in a solitary 

 state ; single specimens met with were thought to be stragglers from 

 swarms. Recent observations have shown, however, that the insect 

 not uncommonly lives a sohtary, or practically solitary, existence 

 throughout hfe, individuals in various stages of development having 

 been found singly 50 miles and more from where any swarms had 

 been known for years. These examples are often distinguishable 

 from t}'pical swarm individuals by the possession of protective coloura- 

 tion. The conclusion has been gradually reached that swarms arise 

 by a rapid increase and gathering together of solitary locusts. Small 

 swarms tend to appear in semi-arid parts of the country in the season 

 following the break-up of a very prolonged drought. The first 

 observed swarms are usually loosely formed, and occur at the same 

 time as "numerous clusters and solitary specimens, all apparently 

 of local origin. In the following season an extensive visitation of 

 t}q3ical swarms may be expected, the position being complicated by 

 migrations of swarms from one part of the country to another, many 

 outbreaks being due entirely to migrants from a distance. 



A repetition of the extensive outbreak of 1915-16, when about 

 28,000 swarms were destroyed, was expected the following year from 

 eggs deposited by the swarms that escaped in numerous localities 

 over an area of about 100,000 square miles, and preparations were 

 made accordingly. The outbreak that materiahsed was less severe 

 and less widespread than was expected. A table showing its incidence 

 is given, covering the whole locust season from August 1916 to June 

 1917. 



Natural enemies exercised but little control during the season. 

 Wohlfahrtia brufinipalpis, Mcq. (locust fly) was observed issuing from 

 egg-deposit sites in one area of severe infestation, but the thorough 

 destructive work necessary involved the sacrifice of this parasite. 

 Large locust birds (storks) were not uncommon in some districts, 

 but only a few were reported from the locust-infested area. Baboons 

 were credited with considerable beneficial work in one area. 



The poison mixture suppHed by the Department of Agriculture 

 consisted of 5 lb, sodium arsenite, 80 per cent, strength, dissolved in 

 half a gallon of water and mixed with a solution of 10 lb. sugar in one 

 gal. water. In use this syrup was diluted in the proportion of one 

 part to 50 parts water, at which strength it acts as a stomach poison, 

 kiUing a locust in from 1 to 4 days. Farmers, however, often use it 

 at a greater strength, when it acts as a contact insecticide, but this 

 use is to be deprecated owing to the risk of poisoning stock. 



The cost to the Government of the 1916-17 campaign was fully 

 £8,000, and this should be considered largely as insurance against 

 damage that might have been done by the resulting migrating swarms, 

 and as a measure against an overwhelming visitation of the plague 

 in the foUomng season, the destruction of a single swarm in one season 

 preventing the equivalent of at least fifty such swarms the following 

 year. Actually, ver^^ little damage was done to crops by the insects, 

 and no losses of stock through accidental poisoning were recorded. 



Field and laboratory studies, the results of which have not yet 

 been published, have been continued on the structure and economy 

 of termites ; the South African Coccids ; the control of the house ant, 

 Pheidole pmictulata, in Pretoria ; and Hfe-cycle studies of Plutella 



