182 



INDIRECT INJURIES CAUSED BY INSECTS. 



It would occupy too much space to notice in detail all the 

 bark-boring beetles which attack the various species of pine 

 and fir trees, which are very numerous, comprising Tomicus 

 pinastri, Laricis micrographus, typographus, andchalcographus, 

 (which I found in 1837, in the larva, pupa, and imago states, 

 in the bark of Norway fir masts imported to Southampton,) 

 Hylurgus piitiperda, as well as two large weevils, Pissodes no- 

 tatus and Pini, which have similar habits, &c. &c. ; and I will 

 conclude the list with stating as a sample of the whole the 

 ravages committed by one of the tribe, Tomicus typographus^ 

 in Germany, where it sometimes attacks the inner bark in such 

 vast numbers, 80,000 being sometimes found in a single tree, 

 that it is infinitely more noxious than any of those that bore 

 into the wood ; and such is its vitality, that though the bark 

 be battered and the tree plunged into water or laid upon the 

 ice or snow, it remains alive and unhurt. The leaves of the 

 trees infested by these insects first become yellow ; the trees 

 themselves then die at the top, and soon entirely perish. Their 

 ravages have long been known in Grermany under the name 



of any kind, which, if any such existed, might be easily seen through their trans- 

 parent skin and body. This absence of all appearance of external and internal 

 organs (the inside of the body seeming filled with granular molecules), added to 

 their shape, which is filiform and very slender, sharply attenuated at each ex- 

 tremity, and their hyaline colour, with very indistinct traces under a'high mag- 

 nifying power of about twenty segments, each as long as broad, are all the cha- 

 racters they afford. These characters, or rather negation of characters, might 

 perhaps suffice to bring these vermicles under the genus Vibrio as formerly ex- 

 tended by Miiller and I3ory de St. Vincent, (to which, from their resemblance to 

 the so called vinegar eels. Vibrio anguilla, I at first referred them,) but scarcely 

 as it has been recently restricted by Ehrenberg, especially as all his species of 

 this genus ( Vibrio) reside in water. From their connection with an animal, they 

 might be regarded as referable to the Oxyuri, were it not that neither my own nor 

 M. Wesmael's close examination could ever discover any trace of their existence in 

 the interior of either the larva, pupa, or imago of Scolytus. Their wholly exterior 

 habitat seems also to exclude them from coming under Professor Owen's genus 

 Trichina, of his group Protelmintha, which, from its shape and simplicity of 

 structure, might possibly include them, but which inhabits the cellular tissue 

 between the muscular fibres, enclosed in a cyst in which it lies coiled up. Leaving 

 it to future examination to decide the true genus and relations of these vermicles, 

 I shall here merely observe, in addition to what has been above said, that I have 

 found them upon a large proportion of the pupa^ of Scolytus destructor, and oc- 

 casionally on some of the larvse in an advanced stage of growth, and also on the 

 pupee of Hylesinus fraxini ; and in such distant localities, and at such diflTerent 

 periods of the year, that I am persuaded that their occurrence was not accidental, 

 but that they are true external parasites, of the family of ScoIytidcB in the pupa 

 (and partly in the larva) state, in which, however, they do not seem materially 

 to injure them, nor prevent them from becoming perfect insects. (See Spence 

 in Trans. Ent. Soc. Land. ii. proc. xv.) 



