104 Zoologica: N. Y. Zoological Society [III; 3 



compared with that of other Silvanidse. Although such genera as 

 Silvanus, Oryziephilus, Cathartus and Nausibius eat by prefer- 

 ence vegetable substances with high protein, starch or sugar con- 

 tent, none of these forms is known to devour the tissue of grow- 

 ing plants, and it is even doubtful whether White's statement 

 (1872) that the Cucujid Dendrophagus crenatus feeds on the in- 

 ner bark of conifers, is correct (see Zoologica III, No. 5). The 

 Tachigalia beetles are primarily attracted by the tree and there 

 is every reason to regard this peculiar Leguminous plant as 

 their only host, so that in this respect, also, they are highly 

 specialized, for while some of the Silvanids, Lsemophloeids and 

 Cucujids {sens, str.) prefer particular trees, they seem never- 

 theless to thrive equally well in trees of different species, 

 probably because they do not eat the living plant tissues 

 but merely require special moisture conditions or the presence 

 of certain other insects. We must .suppose, furthermore, 

 that the social Silvanids are primarily attracted to the Tachi- 

 galia by certain chemical substances in the petioles, a suppo- 

 sition which seems to offer the only satisfactory explanation, as 

 Picard (1919) has shown, for the selection of particular host 

 plants by particular insects. We should have to suppose also, 

 that the beetles can discriminate between the petiolar substances 

 of young shade — and older sun-trees, since they confine their 

 attentions to the former. This is not surprising when we consider 

 that some insects, e.g., certain Cynipid gall-flies exhibit even 

 more delicate powers of discrimination since, when ovipositing, 

 they seem to be able to distinguish between the viability of 

 different buds or leaves on the same branch. 



An even more interesting problem is presented by the 

 coccidophily of Coccidotrophus and Euitausibius, for nothing like 

 it has been observed in any other beetles, and apart from the 

 ants, few insects are known to have developed the ability to 

 solicit honey-dew from any of the Homoptera. I find only the 

 two following cases in the literature, the first an observation by 

 Belt in his "Naturalist in Nicaragua" (1884, p. 228), on wasps 

 attending Membracids : "Similarly as, on the savannahs, I had 

 observed a wasp attending the honey-glands of the bull's horn 

 acacia along with the ants, so at Santo Domingo another wasp, 

 belonging to quite a different genus (Nectarinia), attended some 



