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they are unable to penetrate the hairs covering the unattached end 

 of the egg of Ergolis ariadne, L., or pierce eggs in small heaps covered 

 with hairs, as in the case of Hypsa alciphron, Cram., and Prodenia litnm, 

 F. {Uttoralis, Boisd.). If the host-eggs are laid on leaves A\ath a sticky 

 surface, as in the case of those of H. obsoleta on young tobacco, the 

 parasites are unable to reach them. On the other hand, the Lvcaenid, 

 Lampides {Poli/anwwtus) baetica, L., was not parasitised in the 

 laboratory, but wherever its eggs occur on Crotalaria striata on the 

 East Coast of Sumatra, T. minutum is abundant. 



The follo\\dng is a list of the principal hosts of Trichogramma in the 

 field : Heliothis obsoleta, F., from Physalis angulata, Zea tnays, 

 Macaranga sp., Passiflora foetida, Crotolarm striata, and Momordica 

 charantia; Lampides baetica, L., from Crotalaria striata, C. incana, 

 C. nsaramoensis, Vigna catjang, and P. foetida ; Hippotion celerio, L., 

 from Colocasia antiquorum and C. indica ; Achaea Janata, L. {Ophiusa 

 melicerta, Drury), from Ricinus communis. 



Physalis angulata, Zea mays (maize) and Passiflora foetida favour 

 the development of H. obsoleta. P. foetida is of such little importance, 

 however, that no measures need be taken against it, while maize is 

 cultivated only to a limited extent by the natives. The Physalis is 

 decidedly harmful, as the young caterpillars bore into the fruit-buds 

 and are there sheltered until they migrate in order to pupate under- 

 groimd, whence the adults emerge at the time that tobacco is planted 

 out in the field. Plants useful against H. obsoleta. are Crotalaria 

 striata, C. incana, C. usaramoensis, Amorphophallus sp., Ricinus 

 communis, and Urena tomentosum, though C. striata is the only one 

 of practical value. It must be remembered that Trichogramma does 

 not develop in large numbers on its host living on this plant until it 

 bears fruit, so that planting must be effected sufficiently early. The 

 spread of the parasite is most probably due to the mid-day winds, so 

 that C. striata should be planted in a position which at mid-day wall 

 be to windward of the plantation requiring protection. 



When investigating the distribution of T. minutum in Sumatra the 

 discovery of the Lycaenid host, Lampides baetica, L., on Crotalaria 

 proved to be of the greatest importance, because this plant is almost 

 always found in tobacco plantations, where its use as a green manure 

 is constantly increasing and the eggs of L. baetica abound on it. Most 

 of these eggs are parasitised by T. minutum. 



The conclusions reached are that T. mimitiim can be used against 

 H. obsoleta and perhaps also Phytometra {Plusia), but not against 

 Prodenia, Phthorimaea (Lita) and Botys. The eggs of H. obsoleta are 

 rarely attacked on tobacco because of the stickiness of the young 

 tobacco leaves. The percentage of parasitism of the eggs of this 

 moth on Physalis angulata, L., must be increased, while this plant 

 must be kept down as much as possible. The former may be brought 

 about by increasing the parasitism of other eggs, those of L. baetica 

 on Crotalaria striata being the most suitable. The Crotalaria should 

 be planted round the tobacco field before the tobacco is planted 

 out, in order that the moths may lay their eggs on it instead of on the 

 tobacco. The collection of the caterpillars and spraying with Paris 

 green and lead arsenate are the best remedies in cases of infestation 

 of tobacco. 



