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Over the past couple of years I have been experimenting on the best technique for sterilising Yellow Admiral eggs. The main reason being my ongoing struggle with a disease that has been devastating my Yellow Admiral stock here in the UK. There is no doubt that the main problem is caused by very high densities of insects in a small confined area (10ft x 6ft x 7ft Greenhouse structure). The reasons for trying to maintain such high densities of insects is that Yellow Admirals are not native to the UK and therefore safety in numbers is a reasonable way of making sure I have plenty of time to pull the stock back should any generation fail to produce another. Over the years (15 to date) this has worked very well but recently I have encountered a disease known as wilt which has made the project very difficult to maintain with huge losses of larvae, mainly in the last instar but also at any of the earlier instars. I used to control the health of my stock by sterilising eggs in Formaldehyde solution but this is becoming more difficult to obtain due to it being very toxic if used without precautions, so I embarked on finding a suitable replacement.
I now use a common household cleaner/steriliser, Tradename, Domestos Extended germ kill. When I first tried this on my Yellow Admiral eggs I was convinced it would kill them even at dilute strengths or that at high dilution it would be rendered useless, however I was wrong and this product has proved to be an adequate replacement for formaldehyde.
One of the major differences of using this product instead of formaldehyde is that formaldehyde does not effect the glue like substance the female butterfly uses to stick the eggs to the leaf of the food-plant. Domestos solution dissolves this glue and therefore the eggs will drop to the bottom of the container used to sterilise the eggs in. I found this very frustrating to begin with but it has now been recognised as a significant advantage in achieving maximum hatch rate of the sterilised eggs.
I have found that Domestos is best used at a 10% solution to 90% water as any lower and it may not kill all the disease pathogens and any higher it can dissolve the egg shell and kill the developing larvae. It should also never be used on eggs laid within the previous 24 hours as the shells have not hardened off sufficiently. I normally soak the eggs for 15 minutes in this solution although I have on occasion left them for 20 minutes with few problems.
The major discovery/benefit from using this new sterilisation method is that I can now keep the eggs separate from the leaf they were laid on in a sterile plastic box completely dry and with no risk of mould destroying them before the larvae emerge. After the allotted time in the solution and after removing the leaves that the eggs were originally attached to, (still check as a few eggs still remain attached), I carefully drain away most of the solution by careful pouring, the eggs sink to the bottom so there is little chance if cautious of tipping them away as well. Then after filling this container up with the eggs still inside to full, with fresh water to dilute the domestos I get another sterile container, place a sheet of absorbent kitchen paper over this and after carefully draining the container with the eggs in to 1/4 full I pour the eggs onto the Kitchen paper and let the water drain through. When drained I carefully remove the paper with the eggs on it and place it on several other dry sheets of Kitchen paper to absorb more moisture and leave to dry for 20 minutes. When sufficiently dry I get the sterile plastic box I will store the eggs in and picking up the sheet with the eggs on, using an artists paint brush "carefully" using the tip of the brush sweep the eggs into the box. The eggs are quite hard and bounce like rubber when they hit the bottom of the container. Using this method the vast majority of the eggs will hatch and losses are minimal. One important thing to remember is that you must keep a lid on the box and check at least twice a day for emerging larvae which must be carefully moved using a paint brush to another container with the food-plants as they will starve quite quickly if forgotten. The plastic boxes I use for this sterilisation technique are 73mm x 73mm x 73mm Square stacking boxes as shown in this picture http://www.watdon.co.uk/the-naturalists/acatalog/Clear_plastic_boxes.html
http://www.domestos.co.uk/products/multiuse-bleach.php
If any of the monarch trust members get problems with diseased stock I hope this will help towards a quick and successful solution. I have never tried this on Monarch eggs so be very careful as this species eggs may not be as tough as the Admiral eggs. You may have to vary the experiment yourselves to get it just right for the species you are breeding.
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