Organisms have evolved over the millennia. Over this period, they have adopted different strategies for survival. Many of these strategies have been shaped by the conditions prevalent at that point in time. Also, the strategies are very varied. Species (both prey and predator) have responded to various pressures during the passage of time. Their interactions are dynamic and have led to various checks and balances that one sees in nature.
Recently, I got lucky to witness and document some such interactions involving aphids, hoverflies, ladybird beetles and wasps.
Aphids are small sap sucking insects and are a major reason for a gardener’s worry as they can cause the plants to dry out and die. These soft bodied insects are defenceless against their predators and often can be seen enlisting the services of ants for protection. To get the attention of ants, these aphids coat the leaves with a sweet liquid called honey dew, which is nothing but their excreta! Ants notice this and are attracted to the aphids. They congregate in large numbers and start tending the aphids for the honeydew and in return protect the aphids from the predators.
One morning on our balcony, I observed two hoverflies hovering over potted plants. After a couple of minutes, one of them settled on a drying plant and appeared to be laying eggs. I also observed a couple of wasps joining the hoverflies. A lot of ladybird beetles were going in and out too. After observing all these insects together, I wondered what they all were doing on a plant that was about to die. Upon taking a closer look, I noticed some tiny soft bodied creatures on the plant – aphids. At this point it all started making sense to me and I decided to observe the plant every day.
A crabroniid wasp used to frequent the plant many times in a day and would search for the perfect spot with a good number of aphids. It would bite an aphid, grab it and fly off with the aphid in its mouth. The wasp will eventually park the paralysed aphids in a nest and her brood will feed on the aphids when they are born.
After a couple of days, I noticed the larvae of ladybird beetles all over the plant. In the daytime some of them were observed moulting, while others were seen resting. A majority of them were active during the night, when they used to feed on the aphids.
The larvae of hoverflies also fed on the aphids at any given opportunity.
After the three days, the number of crabroniid wasps increased and the frequency of their visits increased too. Now, there was a new wasp that had entered the scene. I was curious to know what it was up to, as I saw it going under every single leaf as if it was looking for something. I shot a couple of photographs and realised that it was a cuckoo wasp, which was selectively laying eggs on some aphids!
The cuckoo wasp is a brood parasite, which sneaks into the host wasp’s nest and lays eggs. The cuckoo wasp’s brood is a kleptoparasite, which feeds on the food that the host wasp stores for its brood and at times, could also feed on the host wasp’s brood itself. Now the question I had was, why was this cuckoo wasp laying eggs on aphids, while it should be laying eggs in some other wasp’s nest?
I sent photographs and my observations to my friend Sanath Ramesh Manimoole, who was then pursuing his master’s degree in Entomology. He was baffled by this behaviour and he sought help from another expert, Dr Sankararaman. What we found out was that the host of this cuckoo wasp was the crabroniid wasp that was carrying the aphids to its nest. The aphids were being used as carriers and gave the cuckoo wasp a free pass to the crabroniid wasp’s nest.
Nature has its own ways to keep the abundance of different species in check to maintain a balance. Some of these acts may seem brutal, but one cannot help but be in awe at the natural control mechanisms that are in place. Nature will take its own course if we stay away and not interrupt. One needs to be patient and give biological controllers enough time to act instead of resorting to using toxic insecticides and breaking such a delicate chain of events.