Even if you do have greenhouse it is sometimes necessary to have a female to deposit eggs on one plant. There are many techniques for doing this but this is the easiest and cheapest.
After a little research you will know which host plants to have potted in anticipation for this operation. If you have just stumbled into a gravid female there is still hope. If the host plants can be found somewhere else but can be cut, do so as you would with flowers. Place the stems into a soft drink bottle and proceed.
Netting is next and any type will do. Mosquito or 32x32 is cool if you have it. Cheese cloth will suffice if pressed for an alternative. As in the diagram below, place the netting over the host plant. It can then be secured with cord or elastic band to the side of the pot. If the fabric is bit stiff it will stand above the plant. If it just lays on the plant, a framework should be used. The easiest would be to untwine two coat hangers . Remove the hook part and bend the wire until it forms a U-shape. Ditto with the other one. Turn them upside down and place the "legs" into the soil that fills the pot until they are secure. The curved part of the upside-down U's should meet at right angles at the top above the plants. Shazam framework! Now place the netting over the whole frame and secure it around the pot.
If using a soft drink bottle and cut plants, execute the same operation. Place the cut plants into the bottle as if they were a bouquet of flowers. Secure the netting around the outside of the bottle.
When you are ready, place the female under the netting and onto the plant. Resecure the netting. Do not leave her in direct sunlight. She will be too concerned with escaping. Bright day light but not sun light is better. If after an hour or two eggs are not being laid, get a bag. A standard size paper shopping bag is best. Open the bag and place the opened end down over the entire plant and framework, The bag should stand upright by itself. This will take the butterfly's mind from escape to function mode; egg laying.
It is ideal to have several potted host plants ready for this purpose. In this manner once several eggs have been laid on one plant, the female can be moved to the next plant for deposit. The eggs will then be evenly distributed, allowing the caterpillars to be "free ranged" and not stressed out. Actually it will ease the pressure on larvae to become cannibalistic.
These are simplistic approaches to a necessary function to mass produce eggs.
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