Examination of the digestive tract or alimentary canal of insects such as boll weevils, Anthonomus grandis Boheman, (Cate and Skinner 1978, Benedict et al. 1991, Jones et al. 1992, Jones et al. 1993), hoverflies, Melanostoma spp. (Wratten et al. 1995), and lady beetles Chilocorus kuwanae (Silvestri), (Nalepa et al 1992) is an effective technique in determining foraging resources. This analyses consists of removing the digestive tract, then chemically dissolving it leaving only a pollen residue. This chemical process takes about 1-2 hours and uses relatively caustic chemicals.
Although this technique takes longer than exterior examination, there are several advantages to this technique. First, this technique uses equipment and chemicals found in most palynological laboratories. Second, by slightly modifying the technique, the pollen residue can be examined with the aid of light, scanning electron microscopy, or both.
The possibility of the Lepidopteran digestive tract containing pollen due to nectar feeding is currently being examined at APMRU. In preliminary studies, the crop of adult corn earworms (Helicoverpa zea) was examined for pollen. Pollen was found in the crops analyzed. In addition, foraging resources not previously reported were found in the crop analyses.
Pollen analyses of Lepidoptera (moths and butterflies) historically is conducted by examining the exterior of the insect. The entire insect body can be examined. However, usually only the head, proboscis, or eyes are examined. Scanning electron microscopy is usually used for examining the exterior of the insect.
Any insect, honeybees, boll weevils, moths and butterflies, etc., that forage on nectar or pollen can be examined for pollen. Insects become contaminated with pollen when the anthers (plants structures housing pollen) are disturbed. This dislocation can be from brushing against the anther or by wind from the insect's wings when hovering. Some species of flowers have a trigger mechanism that is tripped when the insect (bird or mammal) forages. This mechanism forces the anthers to move away from the flower and hit the insect (bird or mammal) foraging on the flower. Once again, the insect is contaminated with pollen. Pollen also can fall into a flower's nectar when the anthers are dislodged by the wind, insects, animals, etc. Once the nectar is contaminated with pollen, that pollen will be taken into the insect's digestive system or may "stick" to its proboscis when the insect is foraging. Occasionally several types pollen grains may occur in a flower's nectar. This may be due to anomophilous grains (wind pollinated) being blown into the nectar or cross-contamination by insects or other pollinators while foraging. Finding pollen on or in an insect depends not only on determining where pollen occurs on the insect but also on how the insect is prepared for pollen analyses. New techniques in entomopalynology (study of pollen on or in an insect) are being developed to enable better, quicker, and sometimes cheaper examination of insects for pollen. There are three main techniques for pollen analyses: exterior examination, internal examination, and a combination of internal and external examination. Each technique has its own advantages and disadvantages.
