Stick insect reproduction - is it always asexual?

I am a proud owner of five Indian stick insects that I love dearly, and with this specific species, they are able to reproduce via parthenogenesis. I had assumed this was the standard for all stick insects, as, to me, it would make sense as an advantage. However, as a part of my 'The Science of Stick Insects' blog series, I wanted to discuss the advantages of asexual reproduction within stick insects, which is when I discovered that asexual reproduction is actually much less common than I thought, with only 10% of the approximately 3100 species being strictly asexual. Though this statistic makes it seem lower than it is, some species asexually reproduce in culture, especially when a female is isolated from a male, but even then, there is an extremely low hatch rate from the eggs that are produced.

one of my Indian stick
insects

For the species that I own, the Indian stick insect (Carausius morosus), they are asexual in culture and assumed to be sexual in the wild. This is only assumed due to how rare it is to find a male Indian stick insect, with roughly 1 in 10,000 being male. This is likely to be so low because without a male for sexual reproduction, the female cannot produce male nymphs, as their eggs are essentially entirely female. However, in my research, I discovered that stick insects can have andromorphic females, where they are much smaller and have other physical traits like those of a male, but are not true males. But this also means that they are, unfortunately, unable to reproduce at all.

I'll be honest when I say I'm somewhat glad to not have males, as, though they tend to be much smaller and thinner with longer antennae, they also have small wings. They, thankfully, have no function, but it would certainly make me uncomfortable in case I had a unique one which suddenly had the passion and ability to fly. I'm much happier with the females, despite them being much larger (10cm vs 7cm). They have much more of a colour variety (if you can say olive or brown is a colour variety) and have no wings, hence no chance of flying!

In terms of their asexual reproduction, I would say this is highly beneficial due to the basic reasons such as less energy, as they don't have to find another mate, and if they have a beneficial trait, they're able to pass it on essentially infinitely as they form clones. In my opinion, though, the greatest advantage is the rapid population growth since they don't have to wait for a mate. This is because eggs hatch in a range of two to six months, with only a small number of those actually hatching! Hence, being able to continually lay eggs without waiting for a mate is definitely one of the greatest advantages.

However, for every pro there is a con. Such as the identical clones, yes, it's super beneficial should they have a unique gene which makes them amazing compared to their fellow stick insects, but since they're all genetically identical, there's no variation. This means that a disease or environmental change could result in the species being wiped out. On the other hand, the environmental change could work in their favour, allowing them to thrive. Until they eventually overpopulate and have to compete with each other.

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On the other half of the spectrum, where a majority of the stick insects reproduce asexually, I'd like to focus on my favourite stick insect species: the giant prickly stick insect (Extatosoma tiaratum). This is a species is almost strictly sexual, except on occasion when no males are present. There is also a clear difference between the males and the females, with the males being much smaller and thinner, with long wings that allow them to search for females and flee from predators. Can you see why I have Indian stick insects rather than giant prickly stick insects? The females are much larger and much thicker - and, in my opinion, extremely beautiful - they can grow to about 20cm (compared to the males' 11cm). They also live much longer than males, they tend to live for about 18 months whereas the males live for under a year. You can somewhat see on the image, but the females also have wings; they are just too small for them to fly. If they were strictly asexual, I would love to own them, but I assume that they are within a species where they can reproduce asexually, but their offspring weaken every generation due to the lack of genetic variation.

Reproducing sexually obviously has its benefits. As mentioned before, genetic variation is a big pro when comparing the two methods. However, the obvious con is the energy and time spent trying to find a mate, especially considering the lifespan of males compared to females. I can imagine this isn't much of a problem in culture, but in the wild, I can imagine this is a big factor. There is also a problem within the giant prickly stick insect breeders in the UK, as they fear that inbreeding is weakening their stick insects, and so have started breeding with stick insects from abroad. It's nice to see people caring about their babies, but this is another reason why I couldn't have giant prickly stick insects.

Whilst they can also reproduce asexually, it isn't nearly as efficient. I believe that asexual reproduction is a last resort as, like I said before, this normally only occurs when there are no males present, but the time for eggs to hatch increases massively. When reproducing sexually, it takes approximately four months for eggs to hatch, but with parthenogenesis, it can take about nine months. This is an obvious massive difference, as it's about half of a female's lifespan and practically all of the male's.

one of my nymphs (old photo)

Now, if I had any control over how stick insects had evolved, I think the perfect way for them to be is to be mainly sexual reproducers. The genetic variation and reduced time required for eggs to hatch are the greatest pros; and if all species were to stay permanently fertilised (some species have 'sperm storage' and do not require constant mating like others), this would probably allow for the overpopulation of most stick insect species. But I believe that the way of most of these stick insects is the best, because even if constant mating is required, the asexual reproduction being the last resort is the best way to go about it, in my opinion.

Though in my eyes, even though my stick insects are all genetically identical, they are still unique to me, and I love them all equally.