Mummified aphids - an aphid parasitoid at play

Acyrthosiphon pisum (pea aphid) - courtesy of Wikipedia

Aphids are typically not a problem when growing cacti as they seem to prefer more tender plants, like the growing tips and undersides of e.g. Capsicum plants (a.k.a. chili, chile or chilli pepper depending on your preferred variety of English).

Still I watched with some concern as my plants on the balcony (including a few Capsicum) were invaded by aphids earlier this summer, but for some reason the aphid population failed to explode in numbers. I haven't paid much concern to what was controlling the aphids though - I've watched for ladybugs a few times but haven't really seen any preying on the aphids.


The "mummified" remains of an aphid

Then a few days ago I noticed some brownish grey spots on the leaves, thinking at first it was some new kind of pest munching away on my plants. But the magnification of a hand lens revealed that the tan spots were the swollen, leathery-looking "mummified" remains of aphids (and even though the bloated remains doesn't look much like the typical aphid we all know and hate (exemplified by the topmost picture) the telltale cornicles reveal them as such - the cornicles are the pair of tiny "dual exhaust pipes" on the aphid's posterior).

Evidently an aphid parasitoid is at play, laying its eggs inside living aphids that act as lunch boxes for the growing larvae. Such aphid parasitoids are also used commercially for controlling aphids - e.g. Aphidius matricariae are released in many greenhouses.


Larva growing inside immobilized aphid

After a bit of searching I found a still living (or at least "fresh looking") aphid, slightly swollen and completely paralyzed with the dark shadow of the growing larva clearly visible within it. Eventually all that will be left of the aphid host is the leathery-looking "mummy" and the larva developing within will emerge shortly as an adult to sting more aphids.

It's brutal but I side with the aphid parasitoid :-)

Tricotyledon Echinocactus polycephalus seedling

Tricotyledon Echinocactus polycephalus seedling

As mentioned in the previous post I started a handful of Echinocactus polycephalus (SNL 91; Las Vegas, Nevada) from seed a few weeks ago. I didn't achieve impressive germination rates and many of the seedlings were killed off by mold while still enclosed in the humid atmosphere of the germination "tent" - and more have withered after I exposed the seedlings to the harsher environment outside of the plastic bag they germinated in. So for all practical purposes Echinocactus polycephalus (and E. horizonthalonius) live up to their reputation of being extremely difficult to grow from seed.


Echinocactus polycephalus seedling growing its first spines

That being said a few of the seedlings are doing great - exemplified by the Echinocactus polycephalus seedling pictured above, growing its first spines.


Tricotyledon Echinocactus polycephalus seedling - top view

Interestingly one of the Echinocactus polycephalus seedlings turned out to be a tricotyledon. Members of the Cactus family belong to the group of dicotyledons, i.e. their seedlings have two cotyledons or embryonic leaves. So evidently Echinocactus polycephalus is a dicot but for some reason this seedling decided to grow three seed leaves instead of the habitual two.

Polycotyledons could be considered freaks of nature or "mutant" plants but this seedling will probably grow up looking exactly like the other plants from the same batch. The last time I experienced a polycot seedling was some years ago when an Opuntia polyacantha var. hystricina seedling germinated with three seed leaves.


Tricotyledon Opuntia polyacantha var. hystricina seedling

Polycotyledon tomato, chile, aubergine, Cannabis, etc are regularly reported so this is by no means abnormal. It would be interesting to know though if this is affecting the plants in any way (as mentioned, the last time I experienced a tricot seedling the plant grew up to be indistinguishable from the "normal" plants). I'm also curious as to what is causing the extra seed leaves (the Opuntia seedling mentioned above was grown fresh from seed collected in the Grand Canyon; indicating to me that polycots are occurring naturally and are not (only) caused by "mutagens" in the environment).