Maskell. — On Coccidae. 397 



to reopen now the discussion of the generic name, as to which 

 I have somewhat fuhy expressed opinions previously ; but I 

 shall merely refer to my remarks on the subject in these 

 Transactions, and in the " x\nnals and Magazine of Natural 

 History," August, 1895, p. 134. 



It is somewhat curious that the occurrence of this pest 

 on the Nelson oak-trees has never before been made known. 

 The twigs which were sent to me were so thickly covered with 

 the little greenish-yellow tests as to be in places invisible. 

 In Mr. Kingsley's letters he informs me that " the owner 

 first noticed the blight about fourteen years ago." It would 

 appear from Signoret (Iqc. cit.) that P. quercicola was first 

 observed as an injurious pest about 1836, near Paris, and that 

 certain oaks in the Bois de Boulogne were then practically 

 destroyed by it. I have not found any particular mention of 

 it, either in France or elsewhere, since Signoret wrote, as 

 being especially common or injurious, although it has been 

 reported several times in Europe and in America. It is diffi- 

 cult to look at the Nelson oak-twigs without fancying that the 

 countless thousands of insects on them must greatly damage 

 the trees ; and yet all that Mr. Kingsley tells me is that 

 " the upper branches of the trees look somewhat unhealthy." 

 This is after fourteen years' uninterrupted existence. Pro- 

 bably, in Europe there is some parasitic enemy (not generally 

 known) which has kept it in check, and some accidental 

 disappearance of the parasite may account for the prevalence 

 of the PlancJionia in 1836. In New Zealand, apparently, 

 either there is no parasite, in which case the PlancJionia will 

 be able to increase indefinitely, or whatever parasite there 

 may be has for a while disappeared, with the consequent out- 

 break of the Coccids. 



Coccids, like other insects, are subject to sudden and 

 injurious increase at irregular intervals. Just in the same 

 way as in England a few years ago there was an extra- 

 ordinary swarm of the butterfly Colias edusa, so in New Zea- 

 land at one time Lecanium hesperidum was for a few years 

 excessively numerous. In Mauritius and other tropical places 

 Aspidiotus destructor broke out at one time with unusual 

 vigour ; and we can remember here how in the summer of 

 1894-95 occurred an alarming increase of Dactylojnus adoni- 

 dwn in the Hutt Valley, an increase which may perhaps be 

 observed again during the present season. If, therefore, 

 Planchonia quercicola, after being fairly quiescent for several 

 years, has of late suddenly started into abnormal activity, we 

 may expect that after a while the checks (whatever they may 

 be) to its increase will again act on it, and it will return to 

 comparative harmlessness. 



There remains, of course, the chance that the insect is not 



