Mapping & Surveying: Monitoring the Active Replenishment of Subsiding Habitat Project (MARSH) - Insect Survey
A seasonal insect survey is being conducted in four plant communities within the Lee and Hill Marshes. The communities being sampled include Arrow Arum (Peltrandra virginica), Big Cordgrass (Spartina cynosuroides), Reed Grass (Phragmites australis), and Wildrice (Zizania aquatica) . To collect the insects, a tent shaped net is erected with three black light collecting buckets surrounding it in a triangular outline. The lights are left on for a period of 24 hours. The insects trapped in the buckets are combined with those on the net to be treated as a sample of the insect population that lives in that particular plant community.
The fall season study was conducted during October 2001. The results of this study showed that the Arrow Arum plant community not only had the highest insect population but also was the most diverse. Nearly every order of land dwelling insects was represented by at least one species. These representatives live in this community because it is the closest to the water's edge and it is a collecting point for decaying marsh plants, the preferred habitat for detritus consuming insects.
True Bugs are those that feed by piercing their food, either plants or other insects, liquefying it and then sucking it up. Representatives of this type of insect present in the Arrow Arum plant community included the meadow plant bug, ambush bug, aphids, and leafhoppers. Beetles, insects whose front wings are merely hard coverings for the membranous back wings used for flight, were also abundant in the Arrow Arum plant community. Groups of beetles present included rove beetles, ground beetles and leaf beetles. As expected, True Flies were also abundant in the Arrow Arum community. Representative species of this insect group, which are identified by their lack of hind wings, included house flies, mosquitoes, midges, crane flies, and gnats. Flying ants, Caddisflys and Moths were also present in the Arrow Arum plant community.
The Big Cordgrass plant community had much fewer total insects with moths being the most abundant. Only a few leafhoppers, one ground beetle and a few flies were collected. Additionally, two meadow grasshoppers were collected in the Cordgrass community.
The Reed Grass community yields yet fewer total insects with mosquitoes and flies being the most abundant.
The Wildrice community, similar in elevation to the Arrow Arum community, similarly exhibited a larger variety of insects with the leafhoppers and gnats being the most prevalent. Mosquitoes were also plentiful. One additional bug, a backswimmer, was collected at this site.
It has been estimated that half of all animal species alive today are beetles (Coleoptera); using a conservative estimate of the number of animal species, there would be at least three million beetle species on the Earth. Coleoptera means "sheathed wing;" beetles have two pairs of wings, but the first pair has been enlarged and thickened into a pair of hard sheaths, or elytra, that cover the delicate hind wings. Because the elytra are fairly hard structures, beetles have a better fossil record than many other insect groups. Groups of beetles present in the marshes included rove beetles, ground beetles and leaf beetles.
The Diptera are commonly known as (true) flies and include many familiar insects such as mosquitoes, black flies, midges, fruit flies, blow flies and house flies. The major morphological feature which distinguishes flies from other insects is their reduced hind wings. Adult flies have only one pair of functional wings, hence their scientific name-- Diptera (di - two, pteron - wing).
Other less common insects groups collected in the marshes included Lepidoptera (Butterflies, Moths), and Hymenoptera (Flying ants, Wasps, Bees). Adult insects of the Order Lepidoptera can be characterized by the presence of scales on the wings and other external parts of the insect. The name of the order reflects this, with 'lepido' meaning scaly, and 'ptera' referring to wings. Most lepidopteran larvae are herbivores; some species eat foliage, some burrow into stems or roots, and some are leaf-miners. Two pairs of membranous wings, clubbed antennae and chewing mouthparts characterize members of the Order Hymenoptera. The name Hymenoptera is derived from the Greek words "hymen" meaning membrane and "ptera" meaning wings. Hymenoptera are valuable to both man and the environment. Bees, especially, are well known for pollinating agricultural crops and other plants. Even the relatively few kinds of wasps that are apt to sting man when their nests are disturbed are usually predaceous on plant-feeding insects and are decidedly beneficial.
Importance of insect community to birds
Insect communities are a critical prey resource for a variety of birds and fish that utilize the marshes. Lee and Hill marshes support key prey insect assemblages for the predominant bird species observed. During the summer surveys, tree swallows, red-winged blackbirds and marsh wrens were the most detected bird species, while in the winter herring gulls, ring-billed gulls, green-winged teal, Canada geese, dunlin and red-winged blackbirds predominated. Large flocks of tree swallows were observed foraging over Peltandra mix patches that coincided with large hatches of midges (Chironomidae) during the same time period.
Another example, the marsh wren, feeds almost entirely on insects and their larvae, which it obtains on the marsh vegetation or on the floor of the marsh. Much of the food of the marsh wren is obtained near or from the surface of the water and it is not unusual to observe the bird as he sights a juicy morsel fly into the air and capture it in the manner of a flycatcher. Coleoptera (Beetles) and Diptera (True flies) assume the highest rank of prey obtained by the marsh wren, which were also found in the highest abundance in Lee and Hill marshes.
Changing insect communities
In all vegetation types, the highest relative abundance of insects occurred in the flood year 2003, particularly during June 2003. Many insects live in the water during their larval stages or as nymphs. Perhaps, the large influxes of freshwater due to high precipitation (and low salinity) encouraged large hatches of these aquatic immature stages.
Insect assemblage differences among vegetation types were apparent. Overall, the lowest abundance of insects occurred in Big Cordgrass (Spartina cynosuroides) communities, with the highest in Wild Rice (Zizania aquatica). In all vegetation types, Diptera, Coleoptera and Homoptera were in the majority. Diptera dominated communities until September 2003 where it experienced sharp declines that coincided with increases in Homoptera. Homoptera are herbivorous, and their increase may be due to an improvement in the vegetation quality that is consistent with lower salinity. Or there could be other factors in their lifecycle that impact their numbers. The highest diversity of insects was observed inReed Grass (Phragmites australis) communities, followed by Wild Rice (Zizania aquatica), Arrow Arum (Peltrandra virginica), and Big Cordgrass (Spartina cynosuroides). Preferences by particular insect groups for vegetation types were hypothesized based on relative abundance among sites, for example Coleoptera and Thysanoptera preferred Wild Rice communities. Further analyses on the influence of marsh vegetation community types on insects may elicit patterns of use that could be linked to higher trophic levels, such as fish and birds.