An easy method for effectively extending the natural incubation time for phasmids by hibernating eggs at low temperatures. This is especially helpful for species which feed on summer-green food plants only.
The story behind the LTD method
In temperate Europe it is possible to breed an astounding number of phasmid species on easily available plants. Even though the choice of food plants is here, especially in winter, quite limted. Luckily some good food plants are available throughout the year - like bramble (Rubus spp.). Nevertheless some phasmid species will only feed on some of Europe's summer green plants. And this makes it next to impossible for most breeders to breed such species, unless one has a greenhouse at hand. That's a pity, as some of these species are very nice and interesting.
In 2012 we got the amazingly beautiful Calvisia kneubuehleri "Dong Nai" from Vietnam, collected by Joachim Bresseel and Jérome Constant. The first generation we could easily breed on a summer green, unidentified willow species. So the first generation got adult by late summer 2012. As the incubation time for this species is with 7 - 9 weeks rather short, the next generation would have hatched by midwinter 2013. But by midwinter that willow species would not available, it is a summer-green plant. And the first Calvisia kneubuehleri "Dong Nai" generation did not accept any of the wintergreen plants available here in Switzerland. So what to do?.
We decided to put some eggs in the fridge, hoping that the low temperatures will induce a dormancy (= delayed development) or "suspended development" - which then would considerably prolong the total incubation time.
Freshly laid eggs (about 1 week after being laid) have been kept in a common fridge at high humidity (90+% RH) and around 8 - 10 °C. Eggs were in the fridge until mid April 2013, so for almost 4 months. After these 4 months incubation at low temperature, they have been incubated at normal room temperature. And yes - they did hatch after 6 - 8 weeks. Just in time, as by mid May their food plant (that willow species) became available again. That was a happy moment, and proof that eggs of tropical species can successfully be hibernated in a fridge. The total incubation time for these eggs of Calvisia kneubuehleri "Dong Nai" has successfully been expanded to around 6 months. Thus the normal incubation time has been tripled.
And of course we started to experiment with other species too, see results below.
In this connection we made another interesting observation, regarding the tolerance phasmid eggs can have against low temperatures. Once we kept eggs of Eurycnema versirubra (an old parthenogenetic stock from Malaysia) in a freezer for at least one week, at around -10 °C. Nevertheless some perfectly healthy nymphs hatched from these eggs, though only a few.
This incubation at low temperatures we have called the LTD-method. Where LTD stands for Low-Temperature-induced-Dormacy
How does the LTD method work ?
- Use freshly laid eggs, these seem to be more tolerant against the lower temperatures applied with the LTD method
- Put the eggs on dry cotton wool in a small, low container (e.g. plastic bottle cap). The eggs shall NOT directly lay on a humid substrate, otherwise they will get mouldy quickly
- Put that small container in a bigger clear plastic can with wet kitchen paper (or something similar) on the bottom
- Keep the kitchen paper at the bottom of the outer plastic can moist at all times, check regularly
- Close the outer plastic can with a lid, so that a highly humid atmosphere can build up inside
- Make some (pin) holes in the lid of the outer plastic can to avoid condensation. Condensation would facilitate mould growth
- Put the whole LTD unit in the fridge at around 10 °C (the outer compartiments in the fridge door are often places with such a temperature range)
- Make sure that the temperatures stay within a range of 9 - 11 °C, monitor the temperature with a cheap, small digital thermometer
- Incubate the eggs normally after the LTD-period
the eggs are placed in the black, small container which stands on top of the moist kitchen paper at the bottom of the bigger clear plastic container
Side view or such a unit
Top view of such a unit, with Achrioptera eggs
LTD unit variation
Here the eggs are suspended on a removable inset above a humid layer of vermiculite
- The vermiculite can be kept rather humid
- Make (pin) holes in the lid, so that there won't be any condensation within the LTD unit
- Eggs shall not get in direct contact with the humid vermiculite, otherwise they will get mouldy quickly
Side view of such an LTD unit
Top view of such an LTD unit - with Phyllium eggs
- A LTD temperature of around 9 - 11 °C yielded a good hatching ratio (50+ %) for all species tested so far
- If the LTD temperature is too low (around 4 - 5 °C), then the hatching ratio is next to nil
- Other LTD durations than the ones mentioned below are not (yet) tested. But most probably LTD duration can be extended to 3 - 4 months for many (if not all) species
|Species||LTD Temperature||LTD Duration||Prolongation||Hatching ratio|
|Acanthoxyla geisovii||9 - 11 °C||2 months||0.5 x||>50 %|
|Asceles sp. "Cat Tien"||9 - 11 °C||2.5 months||2 x||>50 %|
|Asceles sp. "Cat Tien"||9 - 11 °C||6 months||4 x||>50 %|
|Aschiphasma annulipes "Tapah"||9 - 11 °C||3 months||2.5 x||>50 %|
|Aschiphasma annulipes "Tapah"||4 - 5 °C||3 months||2.5 x||almost nil|
|Calvisia conicipennis "Mulu"||9 - 11 °C||3 months||3 x||>50 %|
|Calvisia sp. "Dong Nai"||4 - 5 °C||2 months||1.5 x||nil|
|Calvisia sp. "Dong Nai"||9 - 11 °C||4 months||3 x||>50 %|
|Calvisia sp. "Dong Nai"||9 - 11 °C||5 months||3 x||>50 %|
|Calvisia leopoldi sp. "Pakung Jae"||9 - 11 °C||3 months||1 x||>50 %|
|Calvisia leopoldi "Pakung Jae"||4 - 5 °C||3 months||1 x||nil|
|Dinophasma saginatum "Mulu"||9 - 11 °C||1.5 months||0.6 x||>50 %|
|Extatosoma tiaratum "Innisfail"||9 - 11 °C||4 months||1 x||>50 %|
|Eurycnema versirubra "Timor"||9 - 11 °C||4 months||0.75 x||>50 %|
|Eurycnema versirubra (partheno.)||-10 °C (freezer)||1 week||few hatchlings|
|Eurycnema osiris "Darwin"||9 - 11 °C||6 months||1 x||>50 %|
|Lobofemora scheirei "Cat Tien"||9 - 11 °C||2.5 months||3 x||>50 %|
|Lobofemora scheirei "Cat Tien"||9 - 11 °C||6 months||5.5 x||>50 %|
|Micadina sp. 1 "Ba Vi"||9 - 11 °C||3.5 months||1 x||>50 %|
|Necrosciinae sp. "Ba Vi, flat wings"||9 - 11 °C||3 months||1.5 x||>50 %|
|Paragongylopus sp. "Hoang Lien"||9 - 11 °C||2.5 months||1 x||>50 %|
- LTD temperature = temperature at which eggs have been hibernated in the fridge
- LTD duration = how long eggs been kept in the fridge
- Prolongation = how much the natural incubation time was prolonged by the LTD-method