|Red Pedilia eating vein of P. megacoriacea leaf|
|Red Pedilia larvae turn pink-orange as does their frass.|
|3rd instar Ptocadica larva on leaf of P. lobata|
Larvae of the Red-white Ptocadica ("RWh") and the Red-brown-white Ptocadica (Ptocadica bifasciata a.k.a. "RBrWh") are similar to Red Pedilia, but with recognizable differences. These larvae have longer legs, and their body is somewhat more narrow, so that the head and legs are more visible from the side. The lobes of the dorsal surface (the "back" of the larva) are rounded rather than pointed, and are very stiff and "armored" looking. The legs are strong. These larvae are more difficult to pick up than Pedilia larvae.
I should note here that I am only 90% sure that these larvae belong to the genus Ptocadica. It is possible though unlikely that they are Monomacra violacea, the Blue flea beetle. For now, to keep things simple, I will assume that Ptocadica is correct. I hope to make a definitive identification in the near future using genetic "bar-coding."
|Tiny RWh Ptocadica larva feeding and growing on P. lobata|
|Red Pedilia larvae hooked to death on P. lobata|
I have found major differences in sensitivity to ant predation (unlike butterflies, beetles are not very vulnerable to ants) and presence of cyanide (beetles avoid cyanide in their diet, butterflies do not). These differences may be enough to prevent flea beetles and butterflies from competing face to face on the same host plant, at least most of the time. Heliconius are generally more successful on the subset of plants which have few predatory ants, including the smaller, more isolated plants that can be searched out by the super-mobile highly visual females. Flea beetles appear to be most successful on larger plants that can sustain "colonization" by less-mobile tiny-eyed beetles (are larger plants more likely to be colonized by ants?), also with reduced amounts of HCN-releasing chemicals.
The similarities have proven more difficult to figure out, but so far they are of the kind discussed above: specific adaptations to overcome specific plant defenses such as hooked trichomes, or, conceivably, special chemical defenses. More about this topic later...