Methods of conservation of larvae

It depends a lot on whether you want to save them for scientific purposes or something else. There are also many options for conservation for scientific purposes, depending on the purpose and methods of research and the size of the larvae. In any case, it is highly desirable to first kill the washed larvae in ethyl acetate vapors of a significant concentration for 3-12 hours (depending on the size), and for medium and large ones, you need to use a highly hygroscopic clean substrate (small sawdust of hardwoods or better vermiculite), preferably with the addition of 10% propionic acid (1 ml per 50 ml of substrate, by spraying). This will provide elasticity and reduce contraction and discoloration. Then the larvae are fixed, in the simplest case - 70% ethanol, but this often does not provide reliable long-term storage and leads to a change in size (shrinking). If you do not intend to measure the size and manufacture sections of internal organs, but only study the external morphology, before fixing, especially large larvae, it is advisable to treat with boiling water (1-3min), and change the fixator 1-2 times within 10-20 days. Use only distillate for dilution, otherwise the salts contained in the water will precipitate on the covers, sometimes very persistent. More successful fixation options for small larvae are:
fixing with a Pampel liquid (per 100 ml: 95% ethanol-30 ml, ice acetic acid 5 ml, 40% formaldehyde-10 ml, glycerol-5 ml, distillate 50%) and storing in it for a long time;
or Buena solution (saturated water solution- p picric acid, 40% formaldehyde and ice acetic acid in a ratio of 15: 5: 1), it is kept from 2h to 2 days (large ones can be stored longer, up to 2 weeks) and immediately washed in 80% ethanol, and then stored in 70%.
In both cases, the larvae can be studied in 70% ethanol and returned to storage, but it is undesirable to dry them. For large larvae, these options are also suitable, but it is advisable to immediately inject them additionally from the inside. There are also modifications of these solutions, especially if subsequent pouring and cutting is expected, for dehydration without significant shrinkage and removal of fats. More often, for studies of external morphology, larvae are dissected without filling, cleaned with hot water or acetic acid, if necessary, soaked in glycerin or filled with Euparal, and examined under a binocular microscope (or preparations of fragments are prepared with electron sputtering). Naturally, in each case there are a lot of small subtleties.
There are also many ways to preserve the external form without the purpose of scientific research, but I don't know much here and I can't specify any optimal one. Look, there were articles, I think, Savitsky 50-ies, there is a description of the old techniques. I know that there are ways to dissect large larvae and fill them with paraffin and celloidin for sections, but I don't know the details. From modern methods that allow storage in the air - I have heard from friends that for large larvae, a good result after soaking, processing with boiling water and pre-fixing with a mixture of ethanol and formalin is obtained by carefully squeezing the contents of the larva through the anus, washing with a fixative, dehydration (I don't remember what) and filling with a transparent two-component silicone injection compound of catalytic curing, before restoring the shape, use a plastic syringe with a thin rod. You can also (I did it myself with similar objects) remove a very detailed working form from a fixed larva by applying a thin layer, and then pouring RTV rubber into a rigid split substrate. Then you can get a three-dimensional copy of the larva from injection-molded plastic or resin (methyl methacrylate, polyurethane, etc.), but you will have to paint it manually.

Vacuum drying.