497 



Such plants show the stems riddled with galleries made by the larvae. 

 Adults may be observed in early June among the larger leaves, the 

 females ovipositing in the tissues of the stem or at the base of the 

 petioles. After two months of feeding by the larvae, first on the 

 leaves and then on the stalk, a pupal cell is formed in the stalk, where 

 transformation takes place. In favourable weather the adults emerge 

 from September onwards, but during bad weather they may remain 

 in the stalks until the following March. The insects are too well 

 protected to be reached by poison sprays, and it would be difficult to 

 reach the parts of the plants on which they feed with any insecticide. 

 The most practical method of control consists of collecting debris, 

 withered leaves and old stalks and burning them. During Julv the 

 larvae will be destroyed by this method, and later on the adults. 



Zetek (J.). Enemigos de la Agricultura y Modos de combatirlos. 



[Enemies of Agriculture and Methods of controlhng them.] — 



Revista la Salle, Panama, iv, nos. 39-45, December 1919-June 



1920, pp. 75-83, 107-112, 140-144, 180-186, 216-221, 245-251, 



[Received 24th September 1920.] 



This paper deals largely with the diseases and hygiene of plants, 



and also describes the preparation of insecticides suitable for contact 



sprays and stomach-poisons. The value of the various insecticides is 



discussed, and the compatibility of many of the usual insecticides and 



fungicides is shown in a table. Suitable machinery for spraying and 



pulverising is described and illustrated. 



CoRBETT (G. H.). Observations on Cotton Thrips in the Gezira, 

 Blue Nile Province, Sudan, in 1918-19. — Bull Entom. Res. 

 London, xi, no. 2, Sejitember 1920, pp. 95-100. 

 Heliothrips indicus, Bagn., has been known on cotton in the Gezira 

 for about three years, and towards the end of October 1918 attracted 

 serious attention. It is thought that the damage done would be much 

 less if the cotton were not so scattered, and the crop for 1919-20 is to 

 be grown in larger areas. This thrips has apparently reached the 

 cotton from weeds growing on fallow land near by or has been brought 

 on the wind. A study of its bionomics was begun in February 1919, 

 when the cotton was recovering from the attack. While the losses 

 caused are considerable, it is hoped that the attacks may prove to be 

 local and to occur only spasmodically. At present, however, this is 

 the most important .cotton pest in the Gezira. Observations made 

 from November to August indicate that there is probably no aestivating 

 period and no resting stage. The differences in the lengths of each 

 stage of the hfe-cycle are remarkable, but under field conditions the 

 whole cycle is a short one averaging about 18 days, and the insect 

 quickly reproduces in large numbers. The egg-stage averages 8 "2 

 days. The larva feeds by piercing and sucking the juices of the 

 plant, generally on the lower surface of the leaves, and remains on the 

 plant from 3 to 6 days. When full-grown the larvae drop from the 

 leaf and crawl into a crevice in the soil, where they change to the pre- 

 pupa and then to the pupa. The insect remains from 4 to 14 days in 

 the soil before the emergence of the adults. 0\'iposition begins two 

 days after emergence, the adult having crawled up the stem to the 

 (717 c 



