I've been experimenting with breeding locusts with the intention of selling them dried for human consumption. It has been a full time effort for over a year and I managed to do hundreds of experiments. While due to local law and bureaucracy I haven't been able to sell, I have been able to devise a simple system in which they grow from egg to adult without a single human intervention. I've mainly done this with Locusta Migratoria, but the same or slightly adjusted system should work for S. Gregaria as well.
The system requires 4 general areas to be maintained and to click together: Feed, Water, Containers, Environment. These are detailed below.
Use super-high quality hay from Annual Ryegrass.
Stuff enough of it in hexagonal wire mesh container.
What I've found is that contrary to popular knowledge, locusts can thrive on dry feed only and reproduce without any issues. This however has to be high quality and is rarely available on the market.
The system requires little or no leftovers from the feed. For this the grass has to be cut relatively early in order to avoid hard stalks and dried properly (indoors ideally) to avoid brown parts, which are ignored by the locusts.
The hay can't be just put loose into the container with locusts, it has to be compressed to save space and remain accessible for about 4 weeks. To this end I stuff it into hexagonal wire mesh container (this mesh is commonly used in gardens, against rabbits etc). Use mesh that has wide enough eyes for an adult locust to go though (2x1.5cm), they will feed both from the top and the sides.
Annual Ryegrass has a number of advantages over many other species (at least in the temperate zone):
Other species of plants work too, I settled on Annual Ryegrass as ideal for the above mentioned reasons. Some other examples that the locusts enjoy in dry form are Taraxacum officinale (dandelion), Dactylis glomerata (orchardgrass) or wheat grass. It is important to know that locusts have a different preference for the same plant in fresh and dry form, e.g. mine never ate fresh dandelion but loved it dried.
Before I settled on making my own hay I have tested many brands of hay and pellets. Pellets are generally ignored by locusts (even if made from ryegrass), only wheat bran pellets are eaten. In terms of hay, the only one I found gets eaten without leftovers is Graze on Grass by Northern Crop Driers (https://www.millbryhill.co.uk/equestrian-c4/graze-on-grass-p742/s1648). However it is chopped too fine to about 4cm pieces, which is too easy for the locusts to drag around the container and thus some part of it gets lost under faeces and never eaten. Another brand which came close quality-wise was Heukoenig (https://heukoenig.de/home/77-2-heuballen-ca-14kg-insgesamt-ca-28kg-1-schnitt-aus-dem-westerwald-4260016580903.html), however it does have some brown parts which are avoided by the locusts until they go really hungry (not ideal for fast growth). Generally available hay for rodents from supermarkets and hobby shops is a waste of time, too many leftovers or is outright ignored in some cases.
For water, provide a closed water container with poly-propylene knots sticking out.
When fed only dry feed, the locusts have to be given water. Instead of fresh leaves, carrots and other things commonly used, I've exploited the fact that locusts are actually able to drink pure water.
This has been the bane of my existence for a good amount of time - how to provide pure water without locust putting faeces or drowning in it. Anything that works as a wick will get devoured, including rock-wool. However, I've made one important discovery. Locusts can only devour it if the fibers are long enough! First you seal a polypropylene knot sticking out of a plastic container with hot glue gun. You give it to the locusts - they will munch on the wick until only a tiny fraction of it is sticking out (I'd say about 0.5 mm), then they are no longer able to eat it. But the ARE still able to drink from it!
The container has to be big enough to last for the whole cycle (or however long you want them to last without human intervention). My boxes supporting about 500 adult locusts in the end (more when nymphs) had grown very comfortably on a 2.3 l container, less is probably also fine. Also depending on how many locusts are in the box, there has to be enough "wick space" - so that many locusts can drink simultaneously if needed. My drinker has 3 x 3 cm spots. To allow locusts to comfortably crawl on the drinkers it is necessary to give them a rough surface - I again used the hot glue.
Use polypropylene boxes 60 x 40 x 42cm (Euro-box) with custom-made lids.
I use polypropylene boxes 60 x 40 x 42cm (Euro-box), https://www.tbaplast.cz/products/euro-container-closed-handles-60x40x42cm
For these I made custom lids with a 10 W LED 6500K light and a steel mesh. The edges are made from plastic profiles bought in a local hobby store: https://www.hornbach.cz/shop/PVC-L-profil-bily-40x10x2-mm-2-m/738272/artikl.html. These are glued together with hot glue gun in a way that they can slide on the box and have a stop, meaning on the long sides it is facing down, on one of the short sides it is facing up. Easier to understand from the photo below. As crawling and molting spots I use the all-too-common egg cartons. Luckily, these can be arranged perfectly in these box dimensions so they hold shape even when you move the box.
This has already been well documented elsewhere, but it is important to keep the environmental values optimal.
Beware that since this system uses no fresh food, the humidity is generally low, equally distributed and constant. You can actually kill locusts with too little humidity - in my experience, under 30% for longer periods is lethal. It is not too hard to go that low in winter time - I had to actually increase humidity by placing water containers next to the heat source throughout winter.
I do not clean the boxes until the end of the cycle. There is an accumulation of frass at the bottom of the box and a high humidity has to be avoided for this reason as well - what I've found is that above about 50% you start to get molds and die-offs.
The set of containers has to be in a room / box with these environmental constraints well regulated. I use a big custom-made styrofoam box (fits about 16 of the locust containers), with heating hooked to a thermostat, lights hooked to a time switch and a ventilator on full-time.
Use 10x10x10cm plastic box with wet substrate, let them lay eggs and place in a new prepared container.
For reproduction I use 10x10x10 cm plastic boxes (bought in Ikea) filled with a commercial substrate for plant replication (no fertiliser). A layer of fine silica sand on the top will avoid mold from frass or hay leftovers, and also keep moisture in for longer, but is not essential.
When the "mating season" begins (generally 1 week after fledging - when you see the males riding on females backs), put these in. Exchange for new one as needed, usually less than a week for a batch of eggs. There will be multiple batches, but each successive batch has less egg pods. In my experience, after 2nd or 3rd batch I do not bother.
Boxes with egg pods are placed in a now prepared container with egg trays, feed and water. The substrate needs to be kept moist - with the sand layer on top it is usually enough to water it once or twice after laying.
The whole cycle happens in the same boxes with the same setup.
One thing I haven't figured out is an efficient harvest - i.e. how to get the adults or sub-adults clean out of the box without much hassle. I have experimented with a bait approach (inserted a small box in the container, with light, fresh grass, a heat source), but only with partial success. Haven't spent too much time on this though.
As probably every locust breeder, I did experience several big die-offs, with dry feed, with fresh feed, with many different setups and at different stages. Lacking a lab and a skill to determine exactly, I believe these were caused by incorrect humidity (too high or too low). I recommend 40% as this seems to be the sweet-spot.
I do not feed wheat bran, as many other breeders do. While it might help them grow faster/bigger, it also makes them contain more fat (more on that here: https://www.ncbi.nlm.nih.gov/pubmed/21319208 ). As the end product in my mind was human nutrition, either whole or as a high-protein powder, more fat was not wanted. The article mentioned above and other sources lead me to believe that the system using only dry ryegrass should produce relatively low-fat locusts, however I haven't tested that.
The size of the drinker, feeder, egg box and proportion to egg trays can very likely be adjusted for more locusts per box.