Feeding habits of Agromyzidae
All Agromyzidae larva are feeders on plant tissue and are mostly known as leaf miners but they also utilise all other parts; stems, seeds, roots and in the case of trees, young trunks and twigs, whilst species in the genus Hexomyza form twig-galls. The majority of species are monophagous, being dependant on one single plant or several species within the same genus. On the other hand, some are oligophagous, feeding on a number of genera within a single family or on several related families of the same order. For example, Melanagromyza aenea is strictly monophagous, being restricted to feeding only on Urtica, whereas Agromyza albipennis feeds on several genera of Gramineae, therefore being oligophagous. Very few species are polyphagous, feeding on a wide range of unrelated host plants. One example of a highly polyphagous species is Liriomyza strigata, which is known from over 240 host plant genera, in over 35 families, worldwide.
The video below shows a Phytomyza obscurella larva feeding, using its mandible to 'scrape' away the plant tissue;
Descriptions and illustrations of the different feeding habits can be found here;
Agromyzid larvae by Graham E. Rotheray
The ease of finding stem and leaf mines makes the Agromyzidae one of only a handful of cyclorrhaphan families whose early stages are reared on a routine basis. Unfortunately, rearing tends to by-pass larvae as subjects of study and what we know about them is rudimentary although indicative of a rich source of information (Dempewolf 2001). The following characters appear to distinguish mining if not other types of agromyzid larvae (Ferrar 1987, Smith 1989):
• mandible vertically-orientated with forward facing hooks (Fig. 1);
• prothorax with anterior spiracles close together at the dorsal midline (Figs. 2& 3).
Widespread agromyzid larval characters not confined to them include:
• head skeleton with intermediate and basal sclerites smoothly adjoined (arrow, Fig. 1);
• dorsal cornu longer than ventral cornu (Fig. 1);
• body segments with rings of red to black micro-hooks or spicules (Fig. 2);
• anus bordered by a pair of fleshy projections (Fig. 5).
Fig. 1. Third stage larval head skeletons, profile views, Agromyzidae on the left and on the right, for comparison, leaf-mining Drosophilidae, arrow points to junction between the bs = basal sclerite and the is = intermediate sclerite; dc = dorsal cornu; h = mandible hooks; m = mandible; op = oral plate; vc = ventral cornu, more information in Rotheray (2019a).
Diagnosing morphology and finding distinguishing characters is one thing understanding how larvae live is another and that requires observations of living material. Realtime observations only go so far, videos are better. Videos provide a means of replaying behaviour at various speeds and forwards and backwards which makes it possible to work out the roles and relationships of morphological components. This in turn leads to an understanding of the mechanisms and patterns of feeding, locomotion etc (Rotheray 2019a). Leaf mining larvae can be videoed using digital cameras on their own or attached to binocular microscopes. Much of what follows was obtained using this method.