LTD-Method                  (Low-Temperature-induced-Dormancy)
 

▷ an easy method for extending the natural incubation time for phasmids effectively by hibernating eggs at low temperatures. This is especially helpful for species which feed on summer-green food plants only

▷ dormancy means "delayed development"

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The story behind the LTD-method

Even in temperate Europe it is possible to breed an astounding number of phasmid species on easily available plants. And many of these plants are available throughout the year - like bramble (Rubus spp.). Nevertheless some phasmid species will only feed on summer green plants. And this makes it almost impossible for many breeders to breed such species, unless they have a greenhouse at hand. That's a pity, as some of these species are very interesting

In 2012 I got a new and amazingly beautiful Calvisia sp. "Dong Nai" from Vietnam, collected by Joachim Bresseel and Jérome Constant. The first first generation I could easily breed on a summergreen, (yet) unidentified willow species, and 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 substitute food plant (the unidentified willow) is not available, as it is a summer-green plant. And the first Calvisia sp. "Dong Nai" generation would not accept any of the wintergreen plants available here in Switzerland. So what to do ?

I decided to put some eggs in the fridge, hoping that the low temperatures will induce a dormancy or "suspended development" which 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+% rF) and around 8 - 10 °C. Eggs were in the fridge until mid April 2013, so for almost 4 months. After that 4 months LTD-period, 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 became availabel again.  That was a happy moment, and proof that eggs of tropical species can successfully be hibernated in a fridge. All in all the total incubation time for these eggs has successfully been expanded to around 6 months. Which means that the normal incubation time has been tripled

And of course I started to experiment with other species too, see results below

Another interesting obervation regarding the tolerance against low temperatures of phasmid eggs. Once I kept eggs of Eurycnema versirubra (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

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How does the LTD-method work ?

  • use freshly laid eggs, these yield a higer hatching ratio than older eggs
  • put the eggs on dry cotton wool in a small, low container (e.g. plastic bottle cap). The eggs shall NOT 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 regularely
  • 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 compartements 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
  • now I use a wine cooler (Rotel Wine Cooler 9021), as in such a cooler it is easier to regulate the temperatures. Other wine coolers should also serve that purpose well enough
  • if a wine cooler with a thermoelectric cooling (like Rotel Wine Cooler 9021) is being used, then the room temperatures should not raise above 28 - 29 °C. Otherwise the wine cooler can not cool down to 11 °C
  • incubate the eggs normally after the LTD-period

 

simple LTD-unit

side view

click here for pic

 

from above with Achrioptera eggs

click here for pic

 

variation of an LTD unit

  • 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 should NOT get in direct contact with the humid vermiculite, otherwise they will get mouldy quickly

     


with Phyllium eggs

 

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Results

 

  • 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 chosen too low (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
incubation time extended byhatching ratio
  Acanthoxyla gesovii9 - 11 °C2 months0.5 x50+ %
  Asceles sp. "Cat Tien"9 - 11 °C2.5 months2 x50+ %
  Asceles sp. "Cat Tien"9 - 11 °C6 months4 x50+ %
  Aschiphasma annulipes "Tapah"9 - 11 °C3 months2.5 x50+ % 
  Aschiphasma annulipes "Tapah"4 - 5 °C3 months2.5 xalmost nil
  Calvisia conicipennis "Mulu"9 - 11 °C3 months3 x50+ %
  Calvisia sp. "Dong Nai"4 - 5 °C2 months1.5 xnil
  Calvisia sp. "Dong Nai"9 - 11 °C4 months3 x50+ %
  Calvisia sp. "Dong Nai"9 - 11 °C5 months3 x50+ %
  Calvisia leopoldi "Pakung Jae"9 - 11 °C3 months1 x50+ %
  Calvisia leopoldi "Pakung Jae"4 - 5 °C3 months1 xnil
  Dinophasma saginatum "Mulu"9 - 11 °C1.5 months0.6 x50+ %
  Extatosoma tiaratum "Innisfail"9 - 11 °C4 months1 x50+ %
  Eurycnema versirubra "Timor"9 - 11 °C4 months0.75 x50+ %
  Eurycnema versirubra (partheno.)-10 °C (freezer)1 week few hatchlings
  Eurycnema osiris "Darwin"9 - 11 °C6 months1 x50+ %
  Lobofemora scheirei "Cat Tien"9 - 11 °C2.5 months3 x50+ %
  Lobofemora scheirei "Cat Tien"9 - 11 °C6 months5.5 x50+ %
  Micadina sp. 1 "Ba Vi"9 - 11 °C3.5 months1 x50+ %
  Necrosciinae sp. "Ba Vi, flat wings"9 - 11 °C3 months1.5 x50+ %
  Paragongylopus sp. "Hoang Lien"9 - 11 °C2.5 months1 x50+ %
     

 Explanations

  • 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