Jan. 1908.J 



17 



PLANT SANITATION. 



Entomological Notes. 



By E. E. Green, Government Entomologist. 



A correspondent from Polgahawela gives me some useful particulars 

 concerning the life history of the red coconut weevil (Rhynchophorus signaticollis) 

 He writes :— " On the 19th July last a tree which was felled to reduce the dense shade 

 over some coconut plants, fell on a two-year-old coconut plant and seriously 

 damaged it, pushing it out of the perpendicular and snapping it below ground level." 



"Within four hours there were red beetles on the tree, and on the 5th of 

 November last the tree was still green, but evidently falling to pieces, and rotten at 

 the base. The tree was removed and carefully taken to pieces by hand. There 

 were eleven empty cocoons with beetles near them— thirteen cocoons containing 

 perfect beetles which began to move about when the cocoons were opened. Of these 

 twenty-four perfect insects eighteen were males. There were some partially made 

 cocoons with grubs in them, and some perfect cocoons within which were insects in 

 various stages of mutation. There was but one grub which was active and had only 

 just begun to make a cocoon. There were no cocoons in excess of the number of 

 insects found, so I take it that none of the beetles had yet left the tree. The whole 

 life-history of this beetle (or weevil) seems therefore to occupy sixteen weeks from 

 the date of the eggs being laid to the full development of the insect. There would 

 hence be three broods a year — approximately." 



My correspondent's estimate of three broods per annum does not necessarily 

 follow from the observed facts. There is sometimes a considerable interval between 

 the emergence of the adult insect, and the deposition of eggs. Moreover, it is not 

 certain that the period of development of the insect is at the same rate in different 

 seasons. It may be delayed by cold wet weather. 



The red coconut weevil having come into considerable prominence lately 

 as a coconut pest, it will be advisable to give it its correct scientific name. This 

 has recently been determined by Mr. H. M. Lefroy (Government Entomologist for 

 India), to whom I sent some of our specimens, as Rhynochophorus signaticollis. He 

 writes me that 72. signaticollis was orgiually described from Ceylon [Ann. Soc Ent. 

 Fr. 6, ii, p. 562 (1882)]. Rhynchophorus ferrugineus is said to be larger, duller and 

 more uniformly coloured — a description that tallies with another (less common) 

 palm weevil that occurs in Ceylon. 



A correspondent writes, asking for advice re " shot hole borer " (Xyleborus). 

 It appears that he has recently obtained tea seed from an estate infested by .this 

 pest, and has been warned by a friend that he runs the risk of introducing the 

 borer by so doing, and that he should take the precaution of washing the seed and 

 burning the bags in which it arrived. My correspondent asks if he should go still 

 further and destroy the seed itself. 



I have replied that there is no appreciable risk in employing: tea seed from 

 a district infested by "shot hole borer." That insect has never been known to 

 inhabit the seed of the tea plant. With regard to the bags, though there may be an 

 off chance of a wandering insect being entangled in the sacking, this chance is a 

 very remot6 one, and the risk from this source is no greater than from the clothing 

 of any person who might visit the estate after travelling through an infected 

 district. Under the terms of the Pests' Ordinance, I have recommended the 

 prohibition of the removal of tea plants from districts in which the pest occur 

 but I have specially exempted tea seed from this prohibition, as being unlikely to 

 carry the infection. 



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