Lesson #4: Pupation
>> Pupae are the third and penultimate developmental stage of mealworm. Once the larvae pupate, the beetles hatch after about 10 days.
If the first mealworms start to pupate, sooner or later, you will find pupae that have dark spots on them. The darkening is caused by an enzyme at the site of the pupa’s injury, which some mealworm might have feasted on. An injured pupa, even if it continues to survive, has only a minimal chance of hatching into a healthy beetle (healthy pupa on the left in the picture, damaged on the right). This brings us to the most significant issue that we must deal with when cultivating the next generation of mealworms, which is cannibalism.
Mealworm – pupae
While this problem is unnoticeable during the rearing of individual mealworms, losses are substantial when rearing all other developmental stages. Mealworms and beetles both enjoy feasting on pupae and eggs, especially when they are exposed to hunger or a lack of fluids. Mixed breeding is, therefore, very inefficient, and we must attempt to separate the individual developmental stages from each other.
Pupation occurs in mealworm larvae under ideal conditions, approximately ten weeks after hatching. The exoskeleton of a larva that rested in a “C” position for a week cracks on its back, and within minutes, a complete pupa emerges from it. Once the shedding process is complete, the pupa does not take any food and without external stimulus will not move.
If you don’t have a very large breeding operation and, on the contrary, have enough time and patience, the intricate pupation process may not interest you much. All pupae just need to be regularly collected and set aside for hatching. Problem solved.
A more experienced breeder, however, will appreciate a less time-consuming procedure.
Pupation of Larvae
First, from the larvae designated for pupation, we sort out the small mealworms. We use a harvesting sieve (2.5 mm mesh) to ensure that only sufficiently grown mealworms undergo pupation. The small, active, and still hungry ones need to be kept out as they might nibble on the pupae. We leave the mealworms on a harvesting sieve for a few hours. They sort themselves out—the small ones crawl down, and the large ones stay on top. We return the small ones to the feeding area and transfer the large ones to a different box. From now on, we can refer to it as the ‘pupation box.’
In this box, it’s crucial to maintain an adequate supply of food and, most importantly, fluids. The pupation box should be regularly provided with a water source (fruit/vegetables, etc.). We partially close the box to limit air circulation and drying, ensuring that the mealworms do not suffocate. Finding the right balance here is challenging—determining how often and how much to moisten. We aim for optimal humidity, but we also want to avoid the substrate turning into sticky mud.
Separation of Pupae
There are two different approaches to how often to separate pupae.
If we have a larger breeding operation and enough space, we’re not so concerned about the efficiency of the process. Instead, we save on human labor, leaving the pupation box to its fate and waiting until the beetles start swarming. We then regularly harvest the beetles, for example, using an egg carton. Simply place it in the pupation box and regularly shake the beetles out into the parent system
However, if we want to achieve maximum efficiency at the cost of some extra work, we remove pupae from the pupation box regularly, ideally every 3-4 days. We can do this manually if there are only a few, or use a sieve for pupae (mesh 3.5 mm), allowing all the mealworms to fall through while the pupae remain.
Quick Separation of Pupae
To separate pupae from larvae, a regular vegetable tray comes in handy.
Mealworm – pupae
We keep pupae from each sorting separately. For this purpose, 5-6 plastic “hatching” boxes are sufficient. By the time we fill the last box, the first one will already be full of beetles, which we’ll move to the parent breeding box. An undeniable advantage of gradual pupae sorting is that we have precise information about the age of the beetles.
There is no need to take any special care of pupae, except perhaps ensuring they are not exposed to excessively high or low temperatures or humidity.
Hatching of Beetles
The hatching of a beetle from a pupa is its final molt in life. A mealworm can go through more than 20 of them in its lifetime. The developmental stage between two molts is called an instar. The last molt is undoubtedly the riskiest. Some pupae are somehow damaged (mechanically/developmentally), so not all of them can successfully hatch into healthy beetles.
If everything goes well, hatching occurs approximately a week to ten days after pupation. Similar to other stages, the newly hatched beetle is initially white, later coppery, and only gains its black color after a few days.
Each beetle is very vulnerable during its first days, does not seek food, and is not very active, so they won’t harm the pupae. By not having pupae from an extended time period in one hatching box, we cleverly avoid the need to separate beetles from pupae, which can be quite laborious and inefficient.
If you still find yourself needing to separate beetles from pupae, simply cover them with cardboard or paper. Large portion of the beetles will eventually crawl onto it. Then, gently shake the beetles from the paper into the parent system. It’s clear that not all beetles will behave exactly as we need them to, and even if we repeat the process several times a day, we will still need to manually sort out some of them.
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