The taste of brine and phloem: The feast for herbivores (June 16, 2014)

Salt marsh elder, Iva frutescens, is the most common broadleaf bush in the salt marshes. This plant tolerates salinity but not frequent flooding, and is thus found at the upper edges of the marsh or along mosquito ditches. As the only “real” non-grassy plant and a relatively succulent one at that, Iva is attended by a variety of herbivores and their predators unmatched anywhere else on the salt marsh. Early in the season before predators and parasitoids catch up with them, plant eaters = herbivores have the upper hand. 

Damage by the end of the season in August

Aphids are the most obvious due to the sheer numbers. Brown ambrosia aphid (Uroleucon ambrosiae) can reach astonishing numbers very quickly. The population doubles in less than 3 days under optimal conditions. Like other aphid species, most reproduction occurs without males, i.e. through parthenogenesis. Live offsprings or nymphs are born every day.

When conditions on the plant become too crowded winged aphids are produced that can disperse to new habitat.

Another common herbivorous sojourner is the chrysomelid leaf beetle, Ophraella notulata. Unlike the brown ambrosia aphid, this little beetle is Iva specialist rarely found on other plants. The larvae look very fuzzy and are often seen in the company of aphids.

Paroxya grasshoppers also consume Iva leaves and are hard to detect. They prefer to hide by hunkering down rather than jumping. The grasshopper coloration and small size allow almost perfect blending in among Iva branchlets.  

Research by Steven Pennings group (http://www.esajournals.org/doi/abs/10.1890/10-0760.1) determined that predators and competition (i.e. “top down”) exercise much more influence on the aphids and the beetles than the plant resource (i.e. “bottom up”).

Unidentified leaf beetle (Chrysomelidae)

As usual, the marsh is full of flies, little and large. Many fly larvae feed on detritus abound in the salt marshes (which is in fact, dominated by detritivores), or are predacious on other insects. This curious fly (Taeniaptera trivittata) belongs to the stilt-legged fly family and behaves very convincingly like an ant. I’ve seen this fly species on the marsh. Is it possible that the larvae can survive in the saline environment? Not much known about the adult habits, but this is a very cool fly to watch.

Yet unidentified crane fly, a common sight early in the season. Who are you, fly?