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As the title states, I'm wondering if diapause is necessary for hatching M. differentialis.
In case I wasn't specific enough, I'm talking about cold-induced diapause that eggs go through during the colder months. I tried to edit my original post to reflect that but it appears that I don't have permission to edit my own posts.
Hi dean, - Slifer & King reported in "The inheritance of diapause in grasshopper eggs" (abstract link = https://academic.oup.com/jhered/article-abstract/52/1/39/819512) that Melanoplus differentialis sometime lay eggs which diapause & sometimes lay eggs that do not diapause. Whether this grasshopper's strain came from more northern regions or were from more southern regions also has some variability in frequency of finding non-diapausing eggs.
Since the above team's non-diapausing strain of M. differentialis was not kept up the team of Oma, Street & Henry in "Establishment of a nondiapause Melanoplus differentialis ... Colony" (abstract link = https://www.cambridge.org/core/journals/canadian-entomologist/article/establishment-of-a-nondiapause-melanoplus-differentialis-thomas-orthoptera-acrididae-colony/91DB9067E31B05A2A862FB3653CD9C21) worked out their own method.
The following may be of use for you since after 10 generations of selective egg choices they managed to create a non-diapausing colony that allowed them to rear 4 generation in 12 months; the time for 1 generation went down to 90 days from the usual diapausing strain of M. differentialis' 167 days (which requires 60-90 days at -10 Celsius of egg diapause stage).
The start for their method was to keep 5th instar M. differentialis in 10 hrs of light at 30 Celsius & then over 4 hours drop the temperature to 25 Celius for 14 hrs of dark. The egg pods were put in moist substrate (vermiculite) & only the eggs that hatched in 6-9 months (just 1 or 2 eggs/pod at 1st) were collected for selective breeding.
These particular hatchlings were then used to breed under similar conditions as above & their eggs used to breed generation after generation for a total of 5 generations from the 1st. After 5th generation only the eggs that hatched in less than 3 months were used for breeding the colony; under same light/temperature described above.
After the 8th generation only the eggs that hatched in less than 2 months were used for breeding the colony. After the 10th generation of selective breeding the females were laying egg pods about every 13-16 days with 87-108 eggs per pod; as mentioned above, completing a generation in only 90 days.
Thanks, this is exactly what I was looking for.
Hi dean, - If you are relying on wild population of M. differentialis & collect their egg pods then consider how Sifer & King in 1943 did things. Although maybe 80% of wild egg pods will have no non-diapause eggs whatsoever; you should be able to find about 1/2% in 100 wild egg pods do have non-diapause eggs (even more than just 1 or 2 sometimes).
To eventually get eggs that would hatch at 25 Celsius in about 38 days this is how they started. They initially kept the eggs for 1st 4 weeks at 25 Celsius (in moist sand) & then cooled them during a 2nd 4 week period at 5-10 Celsius.
After that cycle they returned the eggs back to 25 Celsius (moist sand) & monitored them in order to throw away any eggs that broke diapause. The remaining eggs were then cooled for a further 4 week period at 5-10 Celsius.
Subsequently the eggs were returned to 25 Celsius for another week. As before these were monitored in order to throw away any eggs that broke diapause.
Then remaining eggs were cooled for a further 4 week period at 5-10 Celsius. Following this they eggs were returned to 25 Celsius & monitored for eggs that broke diapause, which were thrown away.
At this stage the remaining eggs that had not yet broken diapause were let hatch. These then became the grasshoppers which became the breeding stock to selectively look for eggs that were non-diapause.
Thanks. I was planning on harvesting wild eggs and seeing if i got lucky with non-diapause requiring eggs but I didn't have any idea about their rate of occurrence.
1-2% in 100 doesn't sound too bad.
I'd actually harvested a lot of M. differentialis last year and allowed them to lay eggs in a tub with peat moss. I let them go through diapause over the winter and hatched them in the spring. They were coming along nicely but a raccoon got into their tub and they were all eaten and/or escaped.
Hi dean, - Allow me to write more clearly about % you might find. If you have a microscope to use you can identify eggs that are likely non-diapausers, after teasing them out of a pod.
Silfer & King did that and actually found 1 pod with 25 eggs in it that were non-diapause. But they considered it an outlier for estimating the % of eggs (not pods) that were non-diapausing among their 100 wild collected pods.
You may find it interesting to know that out of 100 pods they also found 1 pod with 7 non-diapause eggs in that pod, & another 1 pod with 6 non-diapause eggs. In 4 pods they they found 2 non-diapausing eggs. The most pods (5) with non-diapausing eggs had just 1 non-diapauser in a pod.
I've had eggs hatching within the last week. I collected adults for laying from late August until late October. That's almost five months for hatching. Eggs in the wild would be hatching in late spring.
The room I had them in during the winter did get a bit cold on occasion, sometimes down to around 45F/ 7C.
Does it sound like these eggs would have diapaused from that kind of temperature exposure or are these probably non-diapausing eggs that have hatched?
Hi dean - I would be inclined to say those are diapause eggs laid.
A female geting ready to lay eggs has environmental inputs. If it was cooler than normal & the days seemed shorter (less hours of light, more dark) she will lay diapausing eggs.
M. differentialis diapause eggs are laid late summer to fall. In the wild the length of diapause can be weeks to months duration. The age of the female involved is so is a factor.