CGP01 Gall-insect densities on selected plant species in watersheds with different fire frequencies


Long-term monitoring of gall-insect densities on Solidago canadensis, Vernonia baldwinii, and Ceanothus herbaceous. Gall abundances are censused in watersheds burned at one- to twenty- year intervals to asses the role of fire frequency and time since fire on gall-insect population dynamics. The data sets contain the following: Watershed fire frequency, number of growing seasons since last fire, plant species, number of galled stems, and number of censused stems. Censuses conducted for the 1989-1996 growing seasons except 1992 and 1994, next scheduled census is fall 1997.

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To estimate population densities of four common gall-forming insects in the Konza Prairie LTER watersheds. Gall insect populations are studied because they represent an important and diverse guild of consumers and their numbers can be assessed directly by surveying their host plants for the presence of stem galls.


Location of Sampling Stations: Sampling is done in watersheds 001A, 001B, 001C, 001D, 004A, 004B, 004C, 004D, 004F, 004H, 010A, 010B, 010C, SuA, SuB, 020A, 020B, 020C and 020D.

Frequency of Sampling: Once per year. Because a gall provides a stationary record of the presence of the insect that remains as long as the stem remains intact, sampling time is flexible and can be done anytime between August and November. If sampling is delayed onto the winter months, many of the stems may senesce and lodge resulting in increased sampling time and effort required.

Variable Measured: The frequencies of four different gall types on three host plants are measured (Fig. 11). The frequency of round galls of Eurosta solidaginis (Diptera: Tephritidae) and eliptical galls of Gnorimoshema gallaesolidaginus (Lepidoptera: Gelechiidae) are measured on populations of Solidago canadensis (Canada goldenrod: Asteraceae). Frequencies of stem galls of Periploca ceanothiella (Lepidoptera: Cosmopterigidae) are measured on Ceanothus herbaceous (Inland ceanothus or New Jersey Tea: Rhamnaceae). The frequency of galls of Eutreta sparsa are measured on Vernonia baldwinii (Inland ironweed: Asteraceae).

Methods: For goldenrod, a random walk is initiated in the lowland area of the watershed and the first 20 goldenrod clones encountered are sampled. Both gall types are censused by establishing a random transect across each clone and sampling 200 stems. The number of galls of each type per 100 stems is recorded. If the clone contains less than 100 stems, then the number of stems sampled and the number of each type of gall is recorded.

Ceanothus is common in bands along the upper rocky slopes of each watershed. Sampling consists of walking a random transect across the Ceanothus population and establishing a sampling point at every three paces. At each sampling point 100 continuous branches are sampled and the frequency of branches galled is recorded. This procedure is continued for 10 sampling points along the transect. Ironweed occurs primarily in the shallow soil uplands on Konza Prairie. Four random transects are walked through the upland area of the watershed. Along each transect, the first 50 stems encountered are censused and the number of ironweed basal galls (Eutreta sparsa) are recorded. Unlike the other stem galls, the ironweed gall occurs at the stem base and is not easily seen. Sampling is accomplished by sliding the forefinger and thumb down the stem to the base where root branching occurs to verify the swollen tissue at the base of the lowest stem node.

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