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Introduction

Numerous insect species feed on nectar, other plant exudates, and pollen associated with flowers. As a result of this feeding activity, these insects become contaminated with pollen. Pollen can be dislodged from the insect body while foraging. When pollen falls off the insect body onto a new flower, pollen is transfer from one flower to another. This transfer of pollen is called pollination. Pollination is important because pollen contains genetic material which unites with the genetic material in the flower (syngamy). In flowering plants, this union of genetic material ultimately produces a fruit. Fruits in the botanical sense include: strawberries, apples, eggplant, corn, beans, grapefruit, pecans, etc. Producers of today's crops often depend on insects to pollinate their crop's flowers and increase fruit yields. Major insect pollinators include: honeybees, bumblebees, butterflies and moths. Insects visit flowers to obtain nectar or pollen. As they forage, they brush against the part of the flower (anther) that contains pollen. Pollen falls out of the anther and onto the insect's body. Some insects collect pollen (honeybees) and others actually eat pollen. Pollen from feeding activities can be found externally on an insect's body and/or internally in the digestive tract. Identification of this pollen is useful in the understanding of insect migration, and foraging resources (Mikkola 1971; Courtney et al. 1982; Bryant et al. 1991; Hendrix and Showers 1992; Gregg 1993; Gregg et al. 1993; Lingren et al. 1993, 1994, Berkhousen and Shapiro 1994, Loublier et al. 1994). There are several reasons pollen found in and/or on an insect is used for these studies. First, most pollen grains are very distinctive, easily recognizable, and identifiable to the family, genus, and often species rank. Thus, very specific information can be obtained about the plants that serve as adult host and foraging plants. Second, pollen is composed of sporopollenin. Sporopollenin is very durable and does not easily decay. Therefore, pollen remains as a durable natural marker on or in an insect. Third, from the identification of pollen, the geographical origin of the plant from which the pollen came can often be determined. This is especially important when there is temporal and geographical variation in the distribution of the identified plant. For example, pollen grains from citrus flowers (lemons, oranges, grapefruits, etc) were found on corn earworm adults captured in Oklahoma (map). Citrus trees are grown commercially in certain regions of the United States (South Texas, Louisiana, Florida, California, etc.). Citrus pollen found on these insect pests indicates that they traveled to Oklahoma from areas in which Citrus grew. This information is important because corn earworms are an economic pest that attacks corn and cotton. By knowing that these pests migrate from Citrus producing area steps can be taken to reduce their numbers before they infest corn. All pollen identification depends on a good pollen reference collection. This collection is paramount for proper identification of pollen grains. Without a reference pollen collection of vouchered specimens, pollen identification is at best impossible or at worse incorrect.

Historical Overview

Pollen has been used to determine geographic origins since first reported by Pfister in 1895 (Jones 1993) when he examined Swiss, French, and other European honeys and demonstrated the possibility of determining the geographical origin of honey from the pollen within it (Lieux 1969). Parker (1923) discovered that from the pollen found in the stomach contents of honeybees, the source of the nectar being foraged could be identified, and thus the geographical origin of the nectar. Pollen analysis of the digestive system 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) has shown to be an effective technique in determining foraging resources. Pollen analyses have shown to be an important research tool in the understanding of noctuid moths and other insects, their migration and foraging resources (Mikkola 1971; Courtney et al. 1982; Bryant et al. 1991; Hendrix and Showers 1992; Gregg 1993; Gregg et al. 1993; Lingren et al. 1993, 1994, Berkhousen and Shapiro 1994, Loublier et al. 1994).