INSULAR EXPERIMENT STATIONS. 23 



on. In studying the pineapple soils, particularly those on the island 

 of Oahu, where pineapple planting is being rapidly extended, two 

 types of soil were recognized, red and black. In general the former 

 seems better adapted to the crop. A study of the black soils showed 

 in some instances as much as 10 per cent manganese. This is quite 

 soluble and when absorbed by the plants causes them to turn yellow. 

 In the red soils a large amount of ferric hydrate is present and this 

 causes the soils to have a high water-holding power. During periods 

 of heavy rainfall the red soils become saturated with water, result- 

 ing in imperfect aeration. Means are being investigated to overcome 

 the injurious effect of manganese in the black soils and to provide 

 against the water-logged condition of the red soils, so that the culti- 

 vation of pineai)ples will be placed on a more secure basis. 



The entomological work has consisted quite largely of a study of 

 the cotton and pineapple insects and working out methods for their 

 control. Leaf-eating caterpillars were particularly injurious during 

 the year and it was necessary to devote some attention to these pests. 

 Cutworms and army worms attacked a variety of crops, including 

 rice and alfalfa, causing a good deal of damage, but fairly satis- 

 factory methods of controlling these pests have been applied. The 

 army worm appeared in the rice fields in one of the districts of Oahu, 

 causing the destruction of nearly half the crop. This is believed to 

 be without precedent in the history of the rice industry in Hawaii. 

 A systematic study has been begun on the plant lice of the islands, 

 and a number of new species have been found and many important 

 facts regarding their life histories have been w^orked out. Arrange- 

 ments have been made for cooperation with the Bureau of Ento- 

 mology of tiiis Department in the introduction of parasites of the 

 algaroba bean weevil, plant lice, etc. 



A number of miscellaneous investigations were carried on by dif- 

 ferent members of the station staff, among them tapping experi- 

 ments, in which about 500 rubber trees were experimented with to 

 determine tiie best method of tapping, the possii)ility of economically 

 using Japanese labor, the time of day at which tapping should be 

 made, the effect of tapping upon rubber trees, methods of coagulating 

 latex, and the stimulating effect of fertilizers upon the flow of latex. 

 It was demonstrated that trees could be tapped any time from 5 a. m. 

 until noon, and a sufficient flow of latex was secured to indicate that 

 the Ceara rubber tree may be j)lanted in Hawaii on a commercial 

 scale with reasonable assurance of profit. Vertical cuts were found 

 to give better results on Ceara trees than any otiier form of tapping 

 tried. Samples of rubber collected by the station were submitted 

 to experts and were valued at $1 to $1.80 j)er pound, a price almost 

 equaling that of Para rubber at the same date. 



