Survey Methods - Collection / Trapping Procedures

Larval collecting methods considered, as mentioned in the preceding section, included random hand digging and extraction from turf roots as well as quantified sampling using a golf hole plug-cutter. However, when larval identification efforts were unsuccessful within the resources and timeframes of this project, larval sampling was discontinued. Subsequently, only strategies for collecting and trapping adult crane flies were tested and applied beginning in April and continuing until the observed end of adult flight in October.

Several adult collecting approaches were tested, including several forms of passive trapping techniques, active (attraction based) trapping, and ultimately hand or net collecting. Passive trap tests included both emergence and flight intercept (Malaise type) traps. Emergence trapping for many kinds of flying insects that develop on or in the ground can be done very economically using simple cardboard boxes, placed open side down (on the ground), with a clear jar or large vial screwed into the side. Adult insects emerging into the box are attracted to the light of the jar opening and fly or crawl into the jar, where they are easily seen and collected. However, there are numerous significant drawbacks to the technique. The traps are highly subject to tampering in public areas, and finding locations where the traps are protected and can be left in place for more than a few days is difficult. Primary problems (or concerns) include; boxes cause lawn discoloration and spindly growth, are an impediment to mowing and maintenance, are unattractive, and require frequent entry of survey staff onto property for servicing. Additionally, inherent physical problems with the approach include: rain and wind protection, spiders and other predators in the boxes destroy captive adult insects, some insects don't enter or stay in the collecting jar. This last element may be the most limiting factor for use of emergence-box traps for crane fly sampling, as adults are weakly attracted to light. Emergence-box traps were tested at several sites in May to investigate adult T. oleracea emergence from different habitats, but were largely ineffective and discontinued after 1 month.

An inexpensive flight intercept trap was tested, using intersecting white sheet panels and a plastic collector-funnel top similar to a Malaise trap. The collecting principal is based on the tendency of flying insects to fly upward when they encounter a solid barrier, and is an effective survey technique for many kinds of true flies if traps are placed in open "fly ways". The trap was tested in several locations, but failed to collect any adult crane flies.

Adult craneflies are attracted to artificial lights, and several techniques for trapping attracted adults were tested, including the modified light traps shown in figure 8. The hanging traps were constructed from intersecting 1/4" plexiglass panels, standard BioQuip® aluminum funnels inserted into plastic catch bins, and 160 watt, self-ballasted mercury vapor lights (also from BioQuip®). Catch bins were used with either baffles to contain trapped insects or dry ice wrapped in newspaper to paralyze trapped insects with concentrated carbon dioxide.

The modified plexiglass/funnel collector light traps, which work well for collecting moths and other nocturnal flying insects, proved to be very ineffective for trapping adult crane flies, even though adult crane fies were attracted to the vicinity of the lights from the surrounding area. To try to increase trap catch, the hole at the bottom of the funnel was enlarged from 1¼" (32 mm) diameter to 2½" (64 mm), and additional lights (without panels) and multiple adjacent traps were tried. None of these modifications noticably improved trap catch. Several water traps, consisting of a few inches of soapy water in various size and height containers (i.e. 10 gal aquaria, baking pans, etc.) were also placed below the light traps to try a different strategy to capture adults attracted to the area around the lights. These also collected very few specimens. Ultimately, the majority of adult craneflies collected around the light traps were captured by hand or aerial net.

Some hand and aerial net collections were done, both day and night (around various lights), but largely when opportunities presented themselves and were more or less random collections. Some time was dedicated specifically to visual search and hand net collecting, but within the timeframes and resources of this project, was generally too inefficient a technique to use extensively. The same was true for sweep net sampling, which was about as productive as visually spotting and hand netting adults, and much more labor intensive.

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