106 



THE AGKICULTURAL NEWS. 



Afril 



1917. 



INSECT NOTES. 



THE LOCUST INVASION OF EGYPT, IN 



1914-15. 



The rt'iiort of the Ministry of Agriculture in Egypt on 

 the great invasion of locusts into that country in 1914-15, 

 ha-> recently been received, and this opportunity will be taken 

 to give a brief review of the chiet points of interest in con- 

 nexion with this invasicjn, and of the mea-sures taken to deal 

 with it. 



The species in question is the migratory locust (Sc/tisto- 

 cerca peregrina), which has always been as.sociated with 

 Egypt by reason of the fact that the earliest records of this 

 in.?ect are from this country, and because locusts have always 

 had an important influence on the agriculture of Egypt, since 

 the presence or ab.sence of these iiisects Usually meant the 

 failure or success of the crops. The figures of locusts repre- 

 sented on Egyptian tombs dating back to 1400 1!.C. and 

 reproduced in modern works are .so accurate that there can be 

 no doubt that the species concerned was Schistoctn-a per>;griiia. 

 and it is thought that this same species is the one referred to 

 in the Biblical record of the Egyptiari [)lague of locu.sts, which 

 took place about 149U H.f. Their attacks are by no means 

 Confined to the Nile Vallej', but are felt throughout South- 

 western Asia and North Africa. Thi- species breeds normally 

 in Palestine, Arabia, ar.d the Sahara oases, and invades 

 Egypt under favourable weather conditions, an invasion 

 usually extending over the greater part of a year, and breaking 

 in successive waves over diflferent parts of the country. In 

 this connexion it has been noticed that these waves often 

 come when the weather if Egypt is under the influence of 

 a depression. 



The experience of the last thirty years or sO tend to show 

 that these visitations occur abijut every ten years, but it 

 seems very probable that the invasions were much more 

 frequent in earlier times. In previous invasions no complete 

 investigations of this insect had been made, and opportuni- 

 ties of making an extended .study if the life-history and 

 habits, and of working out eflective control measures had 

 been lost. The formation of a Government Agricultural 

 Service since the 1904 invasion resulted in 'a careful investi- 

 gation into the habits and influences controlling the direction 

 of flight of the migrating forms froui their first appearance.' 

 At the same time a record nf the life-history and parasites of 

 the succeeding generations was obtained. 



It was realized that the peculiar local conditions existing 

 in Egypt might necessitate special methods of control. 

 Accordingly, during the course of the invasion all the methods 

 of destruction employed in other countries were tested, but 

 were finally rejected after thorough and practical experiments. 



HABITS AND LIFE-HWTORY. 



Before giving an account of the methods of control it is 

 proposed to mention as briefly as possible some of the more 



characteristic habits of this species, and to outline its life- 

 history. The locusts which reached Egypt in 191-5, although 

 winged adults, were not sexually mature, and the swarm was 

 composed almost entirely of reddish-coloured individuals. 

 At this stage they usually spend the day on the mo%'e among 

 the cultivated lands, while during the night they settle on any 

 available support, suchastreesandshrubs,orfailing these, camp 

 on the ground. It was noticed that the swarms of locusts when 

 in flight a.ssume different positions according to the strength 

 of the wind. 'In a gentle breeze they tty directly up the wind; 

 if the wind strengthens they immediately respond by changing 

 their direction to a diagonal to the wind. In a moderately 

 strong wind they will be observed tlying at right angles to the 

 wind direction, and as the wind velocity increases their line 

 of flight is turned more and more until we find them flying 

 down the wind when a gale is blowing.' As sexual maturity 

 approaches, the locusts gradually change colour, the males 

 becoming a brilliant yellow with their original black markings, 

 and the females also changing to a less extent. 



Egg-laying begins soon after mating, the female drilling 

 a hole in the ground with her ovipositor. The eggs are laid 

 in masses ranging from 80 to 1 20 at the bottom of the 

 cylindrical hole bored by the female, and the space left at 

 the top is filled with a frothy substance. This soon hardens 

 sufficiently to serve as a protection for the eggs, but still 

 permits the emergence of the newly hatched nymphs. The 

 females seem to be very particular in their .selection of 

 a good place for depositing their eggs, and it is stated that 

 a favourite place is always where an inch or two of 

 dry sand covers a moist sand, clay, or silt Banks of 

 canals, railwaj- embankments, and drains or irrigation 

 channel- in the fields are often chosen, and in .such 

 situations the eggs usually occupy a definite zone aftbrd- 

 ing sufficient moisture. 'In cultivated fields the higher 

 parts and infertile patches known as Uior land are very 

 frequently chosen. In some parts of the country eggs were 

 never found among crops, elsewhere the locusts had selected 

 such places freely. This appeared to depend on whether the 

 land was under perennial irrigation or was basin land, crops 

 in basin land usuallj- being avoided; generally the females 

 avoided soil [jenetrated by roots of the plants.' It was also 

 noticed that along the banks of the Nile the eggs were often 

 laid at one particular level above the water, formino a strip 

 of perhaps a metre wide by one or more kilometres long. 

 Above and below these strips no eggs were laid. 'Newly 

 laid eggs are golden brown in colour, but they soon change to 

 a dull gre}' or brown colour, with a faint pinkish tinge ' 



The eggs hatch in from sixteen to thirty-six days accord- 

 ing to temperature and moisture conditions, and the newly 

 hatched nymphs are green, but soon turn black. They do 

 not feed at all during the first four to eight days, even where 

 food is plentiful, but are voracious feeders when once they 

 start. From an early age they tend to climb and cluster as 

 high as possible, kee(jing together in masses, and this habit 

 of massing together has an important bearing on the methods 

 adopted to control them, as will be seen later. This species 

 usually moults five times before becoming adult, but six 

 moults have been recorded. The whole stage from hatching 

 to adult usually oocupies a little over seven weeks. When 

 about to moult the hoppers after the first stage usually cluster 

 together on bushes, or any raised object available. 'The old 

 skin splits along the middle of the thorax and the insect 

 emerges, leaving the empty skin otherwise intact. Empty 

 skins were often found together, in every way looking like 

 a crowd of young locusts.' 



