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Care Guide Series 1:

Beetles

Care Guide 1.5:

Extra tips for breeding flower beetles

Written by Mark Nelson

Introduction

With this care guide we hope to provide more detail on some of the rearing methods already discussed in our other care guide 'Flower Beetles Overview'. The focus here is to provide tips and techniques for producing and caring for larvae/beetles in larger quantities. 

Preparing breeding boxes

 

We regularly prepare breeding boxes so they are ready, should any adult pairs emerge. Then they can be moved straight out of the box where we house the cocoons, to the breeding box. This reduces stress on the beetles and also prevents the freshly hatched beetles from causing any damage or disruption to the nearby cocoons that have not yet hatched.

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Picture 1: Step 1 - Compressed soil

Picture 2: Step 2 - Add decayed leaves

Picture 3: Step 3 - Add decayed logs

Breeding box set up

Step 1: Compress around 2 inches of soil into the bottom of the rearing box. This is something we do not do for all species, but find with some of the larger flower beetles it really helps to encourage egg laying in the females. We usually find that most of the eggs are deposited on or inside this compressed layer. 

Step 2: Add some dry decayed oak/beech leaves and mix it up thoroughly. This should break up the dry leaves crumbling them into fine pieces. 

Step 3: Add some decayed oak/beech logs. They should be soft and rotten enough that they can be easily mulched up by hand and are still nice and white inside. 

Note: For MTU we use a mix of around 80% decayed leaves to 20% decayed wood.

Step 4: Mix the wood and leaf until all you are left with is a fine substrate. A few larger chunks here and there are not a problem, as long as the substrate is more fine than course.

 

Step 5: Add water if necessary. The substrate should clump together and hold its shope when squeezed in your hand, but should not be dripping wet. If it is too dry then add 250 ml water, mix thoroughly and check again. If the substrate is too wet then add more leaf/soil/wood. Mix well and check again. Repeat the process until you have achieved the desired consistency.

Picture 4: Step 4 - Mix substrate

Picture 5: Step 5 - Add moisture 

Stocking densities

The amount of beetles/larvae that can be housed in relation to the size of the rearing container varies a lot from one species to another. There is no perfect formula for calculating exactly what size container to use for any given species. However, there are a few things that can be taken into consideration;

  • Are the males aggressive and how much damage are they capable of doing to one another?

  • How many eggs is each female capable of laying? 

  • How fast is the larval development?

  • The size of the species? Are they likely to damage previously laid eggs when burying?

  • Do they have any special requirements?

    • For example, Dicronocephalus wallichii requires sphagnum moss and dried leaves to create small 'parcels' which it lays its eggs inside. 

  • Are larvae cannibalistic and if so, how quickly will they begin to eat one another if hatching in the same container?

    • For example, Mecynorrhina harrisi is a very cannibalistic species that will begin eating each other in the first instar. Therefore, I would recommend moving adults to a new breeding box every 4 weeks, and that at the same time, you remove the eggs from the substrate and set them up in seperate containers. 

Let's take the Giant African Flower Beetle or Mecynorrhina torquatus ugandensis (MTU) as an example. This should give you an idea of the thought process we go through when approaching a new species. 

  • Males can become aggressive to one another, but with enough space and a ratio of at least 2 females to every male they will usually cohabit without any issues.

  • Each female is capable of laying between 40 and 50 eggs.

  • The eggs will hatch within 3 weeks or so and the larvae will begin to grow relatively quickly reaching the second instar between 4-6 weeks later. 

  • They are a relatively large species with males reaching 80-90mm and females 50-60mm.

  • MTU do not have any particular 'special requirements'.

  • Larvae of similar sizes will live together with little trouble provided the correct care is given. Larvae of differing instars will cannibalise smaller individuals, especially if insufficient care is provided.

Given this information this is how we house our MTU.

Although some fighting between males is good for competition and helps sexual selection, a higher ratio of females to males is always better to prevent the males from injuring one another. They also need plenty of space so the weaker males are able to get away from the stronger ones to avoid unnecessary losses.

  • In a 35L RUB we house up to 1 male and 2 females

  • In a 65L RUB we house up to 2 males and 4 females

  • In a 120L RUB we house up to 4 males and 8 females  

    • This equates  to 1 male: 2 females for every 30-35L of substrate

Every 2 months or so, I move the adults to a new breeding box. This is for two reasons. Firstly, with them being a large species this reduces the chance of them digging up and destroying their own eggs. Secondly, this allows two months between the first and last egg being laid, which helps to reduce the difference in size between the individuals in that box. This in turn reduces the chance of any cannibalism. In a 35L breeding box I house up to 50 larvae in their 1st instars. Once they reach their second instar, I would divide them up between two 35L breeding boxes (up to 25 larvae per box). I have had great success in rearing 25 larvae in a 35L container, from 2nd instar to pupation without any cannibalism. However, care must be taken to regularly check the larvae and change the substrate (every 4-5 weeks).

Checking for eggs/larvae

We leave our adult beetles to it and disturb as little as possible. Food is changed when necessary but if the adults are sitting on the fruit, we leave those pieces until the subsequent food change. In cannibalistic species we check for eggs and remove them to prevent them from hatching in the breeding box and eating one another. The eggs are set up in separate containers full of substrate to allow them to feed happily without disturbing each other. When checking for eggs you must take extreme care as the eggs are so fragile that they will break if handled roughly. Some breeders use a brush or other implement to help go through the substrate, but I much prefer to do this by hand. I find that I am far less dextrous with a piece of equipment and it tends to cause more harm than good. 

Picture 6: Mecynorrhina harrisi egg set up to avoid cannibalism - egg was covered with substrate after photo

If the species is 'communal', then we only begin checking for eggs/larvae around a month after the last female dies. The reason for this is that firstly, it allows the eggs which were laid last plenty of time to hatch before you disturb the substrate. Secondly, If you disturb the substrate too early you increase the chance that you damage any smaller larvae or eggs. Which, for a species that is not cannibalistic, it isn't worth it in my opinion. Instead, you might as well just wait a while longer, by which point the larvae will be larger 1st instars or even 2nd instars, making them much easier to find. They are also much more robust by this point. You can now gently sift through all substrate, moving any larvae you find to a separate container, to be counted, once you are satisfied you have found them all. Then when you do subsequent substrate changes you will know how many larvae to look for, and this will tell you if you have had any losses.

Substrate and Larvae checks

Hopefully, you will discover that your breeding project has been a success by finding a batch of eggs/larvae. In order to see them through to the next generation they will require regular checks and substrate changes (every 4-5 weeks). Once the substrate is ready for a change, carefully sift through and find all the larvae. If all larvae are accounted for then remove half the substrate and top it up with more decayed leaf/wood mulch and mix it all together. Add water if necessary, as described in the 'breeding box set up' above. Then the larvae can be returned to the substrate. The substrate that was removed can then be discarded, or alternatively it makes great compost for plants, rather than wasting it! If all larvae are not accounted for then double check the substrate as you may have just missed them. If after double/triple checking (never can be too careful), then you can assume that there have been some losses.  

 

Note: I often keep bags/bins of substrate for several months just to check them a 4th/5th/6th time which is very over the top. But you would be amazed how many times I have come across a grub in substrate that has been checked 5-6 times already. The sneaky little devils!

 

Losses can be difficult to explain. Some losses are to be expected, so the odd one or two might not be anything to worry about. If you are carrying out a substrate check and have one or two larvae missing , this may be nothing to worry about. However, if you are experiencing losses every time you check the substrate, then this is an indication that something is not right. There could be a number of potential issues;

  •  It may be that the substrate is not being changed frequently enough, which can lead to cannibalism.

    • If the substrate is becoming full of frass (poo), then this can be a sign that the substrate needs a change. 

  •  It could be that the substrate is being checked too often, causing stress. 

    •  This is more likely to result in dead larvae, rather than missing larvae. If you are finding larvae that are intact, but dead for no other apparent reason, then it could be a sign you need to reduce the amount of substrate checks. You should be checking at intervals of 4-5 weeks.

  • The substrate could be too wet/too dry. Squeeze the substrate in your hand as described above (making sure there are no larvae in there!). The substrate should be wet enough that it clumps together without falling apart, but not so wet that any moisture drips out. 

  • It could also be the temperatures. Cold temperatures are not such an issue, so long as they are no lower than 18 degrees C. Hot temperatures, especially if it is reaching 30 degrees C or higher for prolonged periods of time, will be fatal to your larvae and they will need to be moved somewhere cooler. Temperature fluctuations will affect larvae in smaller containers much more than larvae in large bodies of substrate which is why, we keep ours communally wherever it is suitable to do so. 

Remember that it could also be a combination of these factors. If so, fixing one may not solve the entire problem. Therefore, always check through everything to ensure that all the correct requirements are being met.

 

I hope this guide is useful to you. I stand by that what works for one keeper does not always work for another. I know a number of other breeders who all keep the same species using very different techniques, yet each breeder has similar levels of success, despite their different methods. Do lots of research and find what works best for you. 

Thank you for reading! If you have any questions please feel free to send us a message via our contact us page!

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