Remember that Thai Basil bush that I wrote about earlier? The one that came with a free colony of aphids…?
It’s still hanging in there and by now it has even started to flower. There are probably 15 individual plants in the pot, so let’s hope that there is some cross-pollination going on. If I can save some seeds before the aphids kill the lot, maybe I can start a new generation of Thai Basils, and maintain a colony of the (still unidentified) aphids. That is, of course, if there are still any aphids left! Many are now of the winged form and are planning an Easter trip to another plant. Usually a high number of winged aphids is a sign that the colony doesn’t like the plant any longer, or that aphid densities have become too high. Time to move on. The winged ones are now all over my house and crawling all over my tropical aroids too. They seem to just walk around without probing. Certainly nothing is starting a colony. However, plant quality and colony density is not the only thing that is bothering the aphids. Other stressors are appearing too…
I had expected that the insect communities in my living room would be fairly low-diverse, but it seems that some new species always find their way in, ramping up the Simpson Index. Anything can happen in a attic apartment that is surrounded by budding trees, and has windows at canopy level.
So what’s bothering my aphids? Some look a bit strange!
A female parasitic wasp must have been attracted to the infested Thai Basil’s ‘cry for help’. Plants that are under herbivore attack often emit volatile compound blends that can be used as cues by natural enemies of the herbivores. I have never seen any parasitic wasp around the Basil bush, but of course that doesn’t mean a thing. They’re very tiny, and in flight are easily mistaken for a fungus gnat (and I have plenty of those too). But the signs are clear that she has been around. Today, I observed dozens of odd-looking aphids on my Thai Basil. They were completely white, and almost perfectly round. It’s a clear sign that something is eating these (dead) aphids from the inside. The larva of a parasitic wasp, also known as a parasitoid. Female parasitoids lay their eggs inside the young aphids, and can parasitize dozens of aphids per day. They are very prolific, given that they are so tiny. After a couple of days, the aphids turn strange, they mummify. Not long after, a freshly developed young parasitoid will chew a perfectly round exit hole and leave its aphid mummy behind.
Now it won’t be long before the lacewings and ladybugs have found their way into my home and onto the Thai Basil bush – another boost to my apartment’s diversity indices, but it may mean the end of the aphid colony. Cruel nature.