280 



The highest percentage of males was 1-5, in the case of a severe 

 infestation. Only a very small percentage of the females mate. In 

 breeding experiments, conducted for two generations, no difference 

 was found between the results of parthenogenetic and sexual repro- 

 duction, but whether in the latter case really fertilised eggs were 

 deposited was not definitely ascertained. The maximum number of 

 larvae produced by one individual during its life was 87. The adult 

 is attracted by light, but the larvae avoid it. In Surinam this thrips, 

 when beyond the limits of plantations, is always found in sunny, 

 exposed places. Abandoned cacao fields overgrown by wild trees 

 and a wild cacao forest were free from thrips, apparently because the 

 shade was too dense. Heavy pruning has been followed by severe 

 infestation. In the field the abundance of thrips did not show 

 any relation to variations in temperature. The decrease of thrips 

 during the rainy season seems due to conditions unfavourable to 

 multiplication and not to the thrips being washed away, for they are 

 well protected on the lower surfaces of the leaves. The greatest 

 abundance is in times of drought. 



Besides the food-plants already known from the West Indies, the 

 following are found in Surinam : Eugenia javanica, E. malaccensis, 

 Bixa orellana, Canarium commune, Coccoloba uvifera, C. latifolia, 

 Triplaris sttrinamensis and Psidium polvcarpon. Liberian coffee is 

 not a food-plant, though recorded as such since 1901. In all cases 

 the young leaves are preferred, and in some, such as C. uvifera, only 

 these are attacked. 



The author does not agree that this thrips does little damage by 

 itself or that it favours Diplodia. Vigorous trees are soon exhausted 

 by artificial defoliation, resulting in smaller and fewer leaves, dieback 

 and dying of buds. Leaves damaged by thrips are soon shed, usually 

 dropping in 3 or 4 months, whereas healthy leaves remain on the 

 trees 6-8 months. The thrips does not render trees more liable to 

 Diplodia cacaoicola by making wounds in the twigs through which 

 the fungus can enter, as experiments show that feeding and oviposition 

 do not occur on even the youngest twigs. 



A 50 per cent, crop loss is common in badly infested fields in Surinam ; 

 usually it is higher. Sometimes 5 per cent, of the old trees die after 

 attack ; in young trees the percentage is much higher. In some 

 plants (cacao, Mangifera, Anacardium) the leaf -tissue dies at the 

 feeding marks and the leaves are cast, the tree gradually becoming 

 exhausted. In others {Terminalia, Bixa) the leaf-tissue does not 

 •die, and no increased change of leaf occurs, so that the injury is slight. 

 Liberian coffee in Surinam is often attacked by Heliothrips haemo- 

 rrhoidalis, but no injury has been reported, though cacao attacked to 

 the same extent would suffer considerably. 



Natural enemies include Chrysopid Jarv^ae, those of Franklinothrips 

 tenuicornis and F. vespiformis, and a Cephalosporium fungus ; none 

 of them are, however, of importance. 



The following preventive measures are advised : The shade must 

 not be too light and must be uniform ; heavy pruning of cacao and 

 its shade trees must be avoided ; the soil must be kept moist in the 

 dry season. An experiment in manuring with sulphate of ammonia 

 followed by cultivation of the soil proved negative, though the growth 

 ■of coffee on a similar soil would have been promoted to a marked 

 extent. Cultural methods are useless for direct control. The work 

 done with various sprays has already been noticed [R. A.E., A, ix, 439] ; 

 milk of lime appears to be the best. 



