The Miners’ Choice of Food

Abstract

The various aspects of mining which have been discussed in the previous chapters have shown clearly that the mining habit represents a high degree of specialisation in the insect larva. The construction of a mine means that the larva creates for itself special living quarters, of a kind rarely encountered in other types of existence, but bearing some resemblance to feeding channels in stems or roots. This endophagous method of feeding, however, also represents specialisation in the type of food. In contrast to external feeders, mining larvae only consume certain plant substances; the larva has become more selective than free-living forms and no longer indiscriminately eats the whole tissue of the plant but has specialised in certain substances, on which it relies for its nourishment. In contrast to the external feeder, it avoids eating certain plant tissues which it finds of little value, such as the epidermis which is of relatively low nutritive content; furthermore, the epidermis is frequently covered with a protective skin, the cuticle, which can only be digested with difficulty or not at all and which is of course eaten by the external feeder and merely represents superfluous ballast in the digestive system. Although the mining habit in itself represents a specialisation in the choice of food, we nevertheless find that miners carry this specialisation very much further. This specialisation should be considered from three different angles: first, which tissue of the plant is eaten, secondly, which organs of the plant are attacked and, finally, it is of interest to know which species of plant are preferred. Miners, or at least the great majority of permanent miners, unlike external feeders, affect only a single species of plant on which the egg has originally been deposited; in general this food plant cannot be changed and it is particularly interesting to investigate which plants are favoured by each mining species and which, on the other hand, are rejected. The problem of the selection of the food plant devolves in most species on the ovipositing imago; this, however, in no way detracts from our observations. It will be seen that in the majority of cases the selection of the food plant is not haphazard, but is subject to certain regular patterns which often clearly illustrate the ability of the species concerned and give a highly interesting insight into the inter-relations between plants and insects.

The online version of the original chapter can be found at http://dx.doi.org/10.1007/978-94-015-7196-8_34