November, 18&0..1 277 



HOW DO COCCIDS PRODUCE CAVITIES IN PLANTS? 

 BY W. M. MASKELL, F.E.M.S. 



Every student of the Family Coccididce must have noticed how, 

 besides the general damage which, in many cases, they inflict upon 

 the plants they live on, they produce, or induce, local particular in- 

 juries on the various parts, or at least notable alterations of form or 

 texture. All Coccids do not seem to be mortal foes of vegetable life. 

 Many of them, indeed, destroy more or less rapidly the health of a 

 plant and kill it ; naturally in so doing they render it unsightly. 

 Others cannot well be said to be murderous in their attacks, but they 

 do their best to spoil the appearance of plants. Others again are 

 neither very ugly nor very injurious ; still, in the spots which they 

 affect, they produce local alterations of form which of course are not 

 natural to the plant. Some of the most harmful, as for example 

 Icerya Purehasi or Mytilaspis pomorum, seem to exercise no influence 

 on the shape of a plant ; they waste it away without altering the form 

 of the twigs or leaves. Others produce swellings or "galls " on wood 

 or leaf which, in proportion to their own size, are enormous. I have 

 before me at this moment a branch of Cnsuarina from Australia in 

 which an insect (discovered lately by Mr. C. French, F.L.S., of Mel- 

 bourne, and as yet not sufiiciently identified) has produced such galls. 

 This very curious Coccid, itself of a conical shape, averages scarcely 

 one-fifth inch in diameter and one-sixth inch in height ; one of its 

 galls on the twig before me is as big as a large walnut, and is doubtless 

 not exceptionally large. These Coccid galls may probably be accounted 

 for, as they usually are in entomological works, by " irritation of the 

 tissues consequent on the suction of the plant juices through the 

 rostral tubes of the insects." I do not think the explanation is en- 

 tirely sufiicient, as it does not account for the absence of galls in a 

 majority of instances ; as all Coccids work in precisely similar ways, 

 and extract the plant-juices by means of suctorial tubes, it might be 

 expected that similar results would follow, yet the gall-producing 

 Coccids are probably only a very small minority in the Family. 



But there is another proceeding adopted by some Coccids which 

 is much more puzzling. Allowing that, in plants as in animals, irrita- 

 tion may produce inflammation and consequent swellings, it is not 

 easy to understand how these insects manage to burrow into, and form 

 cavities in, plants. It may, I think, be fairly concluded from the fact 

 which I have just mentioned, viz., the scarcity of Coccid galls, that 

 Coccids do not secrete any acrid or acid fluid which, {xissing through 



