Plant Sanitation. 



18 



[Jan. 1908. 



I have received specimens of the caterpillars of the Tussar silk moth 

 (Antheraea paphia), said to have been found feeding upon the leaves of a Para 

 rubber (Hevea) plant. The caterpillar is a large and voracious one, and would soon 

 defoliate a small plant ; but its appetite would quickly draw attention to its ravages, 

 and being a large and conspicuous insect, it can be readily seen and destroyed. 



The caterpillar is of a brilliant apple green colour, with vivid orange spots 

 on the prominent tubercles. 



Plant-feeding caterpillars are usually unmitigated pests. But I have 

 received specimens of the caterpillars of a common moth (Plusia oxygramma, Hubn.) 

 with the report that they are doing excellent service in destroying a troublesome 

 weed {Conyza sp.). My correspondent writes: — "1 have a plot (of tea) of several 

 acres under very heavy weeds, this weed (Conyza), Ageratum, and a weed like 

 groundsel. The caterpillars are leaving the other weeds but making an absolute 

 clean sweep of this particular weed, eating all the leaves and the top— except the 

 ribs. I think all these weeds will die. What I want to know is, is the poochie 

 harmless, and ought it to be encouraged ; or should it be exterminated as a pest of 

 tea, rubber &c. ?" 



I was able to assure my correspondent that these caterpillars are very un- 

 likely to attack the tea or any other estate produce. They are, however, some- 

 times troublesome in a kitchen garden, where I have known them to play havoc 

 with a bed of tomato plants. 



Outbreaks of ' Red slug ' (Heterusia) have been reported from several dis- 

 tricts. This caterpillar confines its attentions to the older leaves of the tea plant 

 and does not appear to relish the young flush. Extensive defoliation of the mature 

 foliage will, however, weaken the bush. If the tea is nearly ready for pruning, 

 this work should be taken in hand at once. The prunings should be burnt in situ, 

 together with all fallen leaves and rubbish from below the bushes. But if the 

 pruning of the tea is inadvisable at the time, little can be done beyond collecting 

 the caterpillars by hand. At the same time, the rubbish and fallen leaves should 

 be sweptup and burnt, as many of the caterpillars will have formed their cocoons 

 amongst the dead leaves. 



This caterpillar is fortunately very much parasitized by a species of fly 

 (Exorista heterusice) which very materially aids in checking the pest. 



If the earlier attacks are detected, and the caterpillars collected and des- 

 troyed while the insect is confined to a few bushes, further and more extensive 

 trouble will be avoided. 



I have received specimens of Cajanus indicus— the ' Pigeon Pea ' or ' Dhal ' 

 of India— with the leaves thickly covered with a 'mealy bug' (Oudablis sp.) to 

 such an extent that the whole plant appears snowy white, I am not aware that 

 this plant is cultivated to any extent in Ceylon, but the pest might be a serious 

 one if introduced into India. 



Specimens of plantain fruits have been submitted to me with their skins 

 badly infested by a ' scale-bug ' (Aspidiotus destructor). The quality of the fruit 

 does not appear to be affected in any way, though the presence of the bag is a 

 distinct blemish to the appearance of the fruit. 



The aquatic larvae of Dragon flies form a considerable portion of the food 

 of imported trout in Ceylon. 1 have had the opportunity of examining the 

 contents of the stomach of a medium-sized fish, which contained little else than 

 the remains of these larvae. But they take their revenge in the stew nond where 

 the large species take heavy toll from the young fry. In fact, in two cases that 

 have come under my notice, they appear to have been responsible for the extermin- 

 ation of practically the whole stock of young fish. 



