LES PRINCIPAUX ENNEMIS DU CACAOYER AUX ILES DE SAN-THOME, ET DE PRINCIPE

LES PRINCIPAUX ENNEMIS DU CACAOYER AUX ILES DE SAN-THOME, ET DE PRINCIPE. Rapport sur une Mission d 'Etude Agricole et Phytopathologique. By Henri C. Navel. Pp. 127; 53 photographic reproductions, 2 maps, and 4 coloured plates ; Svo, 10 X 6}. (Paris : Emile Larose, 1921.) The Direction of the Society of Emigration of San Thom and Principe, alarmed by the damage which was being caused to the plantations of those countries by the various enemies of the cocoa tree, despatched a Mission in 1919 to study the different affections and to suggest the best means of combating them. With this end in view, M. Henri C. Navel visited nearly all the plantations of both islands, and the material collected was determined at the National Museum of Natural History at Paris, M. Navel divides the principal enemies of cocoa into three groups : (i) Maladies which are not due to parasitic attacks, but are caused by wounds, the action of the soil and climatic conditions, the want of hygiene in planta- tions, the suppression of shade trees, bad procedure in planting, etc. ; (2) the parasitic insect enemies which attack with more virulence trees already under the influence of the maladies in the first group ; and (3) the cryptogamic parasitic enemies, of which a certain number attack plants in a good state of vegetation, whilst others are induced by the presence of the influences mentioned under the first two groups. The author points out the effect of erroneous cultivation, due to the suppression of shade in the drier districts, where the process of " piquage," a destruction of natural shade by ringing the forest trees, is commonly practised, and compares it with the conditions of growing cocoa without shade in the elevated regions, where rain falls more frequently and where the depressions in the soil are such that shelter and shade are naturally provided without the necessity of extraneous tree growth. With regard to insect pests, a species of thrips (Heliothrips rubrocinctus , Giard) is said to cause the greatest damage. This insect was introduced into the islands from Brazil and now occurs everywhere, being most prevalent in those parts where the diminution of shade trees is taking place. Various beetle and moth larvae are referred to, which attack the trunks by boring, and white ants are also mentioned as enemies. A beetle (Nistora theobromce, Labois) and a Helopeltis, identical with that found on the mainland of West Africa, attack the fruit and mark it with their puncturings, which permit of infestation by fungoid pests, leading to the destruction of the whole fruit. The author gives an illustration of Sahlbergella singular is, Hagl., which he records from the Belgian Congo and which with S. theobromce, Distant, is perhaps the worst pest on cocoa in the Gold Coast. Neither of these parasites appears to have been met with at San Thome or Principe. Several fungoid pests are dealt with, including a mildew (Phytophthora Faberi, Maubl.) which is very injurious to the fruit. The volume should be of great utility to planters and others in the West African cocoa plantations.