This observation has been registered in the iNaturalist database with the following accession 105647409.
Observed on August 9, 2014 at the Georgia State Botanical Garden in Athens, GA, USA. Here, you can see a number of cone-headed planthoppers (Acanalonia conica) feeding on a passion flower vine (Passiflora incarnata). The passion flower family (Passifloraceae) is well known for its sugar producing glands called extrafloral nectaries. These nectaries attract ants and here in this observation we see two species of ants (Formica palidefulva and a Crematogaster spp.) patrolling the passion flower.
This observation could be a first in reporting Passifloraceae among the host plant families for the cone-headed planthoppers.
In some plant-animal systems the function of the extrafloral nectaries can be hijacked by aphids tapping deep into the vasculature with specialized mouthparts. In these systems, ants do not defend the plant but instead protect and tend the aphids. This is advantageous for the aphids since ants are especially effective against ladybugs and wasps. Released from predatory pressures, aphids can suck large quantities of the plant juice. Therefore with this surplus, aphids can afford to provide energy rich sugary honeydew for ants. The sugar containing excretion must be rather viscous and hard to drop off from the butts of the aphids. However, the continual removal of honeydew by ants could be relieving the aphids increasing the throughput.
For most of the time, ants assume antiherbivory or antipredatory roles. However it is different this time: Despite the presence of extrafloral nectaries intermittently bribing ants for protection, the ants do not or cannot chase the planthoppers away. How can the planthoppers bypass the ants’ defense? Could the cone-headed planthoppers be drawing so much liquid, enough to reduce the volume secreted in the extrafloral nectaries? Perhaps with insufficient nectar bribe, the ants become less interested in the plant and become less aggressive. Another possibility is that cone-headed planthoppers have evolved a pair of articulately patterned leaf-like wings. The high-degree of mimicry in the wings could be successfully tricking the ants to recognize them as a part of the host plant. The significance of wings in the insect world transcends flight. The picture wing fly shares the same host plant with the green cone-headed planthoppers however patterns on their wing appear to mimic jumping spiders. Ants aggressively chase the picture wing flies away from the extrafloral nectaries.
There could be some energetic gain for the planthoppers. Since they possibly keep all the sugar in the nectar to themselves, their excreta must be less viscous and easier to discharge. Moreover, the sheer presence of ants may also deter planthopper enemies such as young praying mantises, ambush bugs, assassin bugs and spiders. Caterpillars of the epipyropid moth (Fulgoraecia exigua) are known to parasitize A. conica.
A parallel observation is from a tropical arboreal ant called the Bullet Ant (Paraponera clavata). Bullet ants have a powerful bite and can sting very painfully. The workers are so big that when they move from one leaf to another the leaves bend under their weight. The following video shows a worker patrolling on a piper plant at La Selva Biological Field Station in Costa Rica. Like the Malaysian Giant Forest Ant, the Bullet Ant workers are specialized on plant nectar. This foraging individual makes a few repeated stops to check out the water droplet hanging on the very tip of a petiole. Curiously, while patrolling she appears to ignore a planthopper feeding on the sap of the plant:
2 Comments