Life History of the Mining Insect

Abstract

After fertilization, the female lays its eggs (although ovipositing frequently takes place in Tenthredinidae and sometimes in other Orders without previous fertilization, in other words parthenogenesis occurs). Ovipositing assumes different forms according to the Order or family. In very many cases the egg is attached to the leaf on the outside of the plant tissue. It is cemented to the leaf surface with a sticky secretion and the empty egg-shell is still visible after the larva has hatched and is frequently a valuable guide to identification. In certain cases the egg is covered by a varnishlike substance which gives it added protection, especially in Buprestidae, whose mines can easily be recognised by the shiny secretion covering the egg (Fig. 49). The egg may be laid on the upper or lower surface of the leaf and the side of the leaf chosen is usually characteristic of the species concerned. Mines closely resembling each other, such as those of Nepticula on Rosaceae can often be differentiated by the side of the leaf on which the egg is to be found. In this genus, especially, the eggs are often laid in a well concealed position, frequently in the angles of the veins where they are difficult to find, especially when this part of the leaf is more hairy than elsewhere. In such species the mine track which is more easily visible should be followed back to its origin, where the shell of the egg can be found. A lens with a magnification of 20 always makes an examination of the egg possible without difficulty. There are some species which do not lay their eggs in the exact spot where the young caterpillar will later commence its mine The females of Hyponomeuta, for instance, deposit their eggs in groups on the cortex of the stem or twig where they pass the winter and only in the spring do the young caterpillars seek out the leaves, which they burrow into. This is, however, an unusual exception and in almost all cases it will be possible to observe the type of oviposition at the commencement of the mine. When the larva has already changed its mine this is more difficult and the original mine must then be looked for in the vicinity of the secondary mine in order to establish the type of oviposition.

The online version of the original chapter can be found at http://dx.doi.org/10.1007/978-94-015-7196-8_29