May 1907.} 



297 



Plant Sanitation, 



flies were said to be found perched on the ends of the stumps, engaged in sucking 

 the sap ! This is, of course, an error of observation. Dragon-flies are purely- 

 insectivorous and— far from occasioning any injury— should be regarded as highly 

 beneficial insects. They are fond of taking up their position on any vantage 

 ground from which an uninterrupted view is obtainable on all sides. This will 

 account for their presence on the ends of the rubber stumps. From such a perch 

 they would be ready to pounce upon any smaller insect that might come within 

 their range of vision. 



With reference to an earlier note (" T. A ". Dec, 1906), on a boring beetle in 

 camphor plants, it appears that this is not the only insect that is undeterred by 

 the presence of camphor in the wood. In a recent report issued by the Jamaican 

 Board of Agriculture is a note on a species of Weevil (Hilipus elegans, Guerin) 

 which tunnels into the stems and larger branches of the camphor trees in Jamaica. 



Castor-oil (Ricinus) plants, on the Silk Farm, Peradeniya, have been badly 

 infested by a ' scale-bug,' Diaspis pentagotia, Targ. The insects are massed round 

 the collar and lower parts of the stem, resulting in decay of the cambial tissues and 

 the consequent death of the affected plants. 



The specimens of ' Copra ' (dried coconut) in the R. B. G. Museum have been 

 completely destroyed by the larvse of a Pyralid moth (Ephestia cautelta, Walk). 

 This little insect is destructive to many kinds of stored foods. I have previously 

 bred it from almonds, dried cacao beans, and cake-chocolate. 



Considerable and annoying loss in vegetable and flower gardens often occurs 

 from the attacks of an ant {Dorylus indicus). These little insects are often mistaken 

 for Termites, but are true ants and not even distantly related to the ' white-ants.' 

 They will tunnel into the tubers of potatoes and dahlias and attack the roots of a 

 large number of other plants. ' Vaporite ' will be found an effective check to this 

 pest. It appears to be fatal to all subterranean insects. But it must be applied 

 carefully, or it may injure the plants also. The best plan is to mix the Vaporite with 

 the soil (in the proportion of 1« oz. to the square yard) about a week before the 

 plants or seed are put out. When applied to growing plants, it should be dibbled 

 into the soil at a little distance from the roots. 



In Theobald's ' Monograph of the Culicidse ot the World ' (Vol. IV., p. 1), the 

 value of ' duckweed ' (Lemna) as a means of preventing the breeding of mosquitoes 

 is put forward with strong corroborative evidence. It is suggested that this plant 

 might be cultivated in many ponds and pools where mosquitoes now habitually 

 breed. The ' duckweed ' forms a close covering on the surface of the water and 

 constitutes a mechanical obstruction to the deposition of the mosquitoes' eggs. 

 Two species of Lemna (paucicostata and polyrhiza) occur in Ceylon, and are recorded 

 by Trimen as common. But the only locality in which I have observed pools densely 

 covered with ' duckweed ' is Anuradhapura. Another plant that should be equally 

 or even more useful is the Utricularia, several species of which flourish in still water. 

 These plants have numerous small bladder-like organs in which small insects become 

 entrapped and killed. 



