[Training Update] What's in a Name?

Precise identification of offending arthropods (which includes insects, mites, ticks, spiders and scorpions) is extremely important in pest control and may have far-reaching economic or medical implications. For example, some wood-infesting beetles do not re-infest boards they emerge from and thus are not a problem. Others do, however, and must be dealt with aggressively to prevent major structural damage. Also, a person bitten by a nonpoisonous spider does not need the expensive and intense treatments that a person bitten by a poisonous spider needs. Obviously, accurate identification is crucial from the outset.

Entomologists use their own jargon and terminology and this sometimes makes life difficult for pest control personnel. However, this terminology can be deciphered once the reader understands the basis for arthropod naming. Generally, arthropods are grouped into classes, orders, families, genera and species according to shared common morphological structures. Specimens with eight legs and two body regions are placed in one category, specimens with six legs and three body regions are placed in another, etc. Making things easier, many times the names assigned to these categories are descriptive of the arthropods in that category. For example, insects with two wings are placed in the order Diptera, meaning two wings (see box below for other insect orders). Further, specimens may be placed in a "family" based upon certain traits. For example, mosquitoes are flies (two wings) with a long, blood-sucking proboscis and scales on their wings.

The species name of an organism consists of two words — genus and species. For example, humans are in the species Homo sapiens. Often, there are many species in the same genus, meaning they are all closely related. For example, there are several cockroaches in the Periplaneta genus. Accordingly, two roaches in the genus Periplaneta would be more similar than, say, one roach in Periplaneta and the other in Blatta. Keep in mind that all organisms are classified into groups with common morphological characters.

Also, species names may describe the arthropod — Buggus erythrocephala would mean having a red head, the term melanogaster would mean dark or black belly, the name Calliphora vomitoria or C. cadaverina for a blow fly would give the reader some idea of what kind of things these flies are attracted to or breed in. However, not all names given to arthropods are descriptive of the organism; some memorialize a bug specialist.

Buggus parkeri, bacoti, kochi, blakei, walkeri or goddardi (sorry, I had to include myself) would be named after Drs. Parker, Bacot, Koch, Blake, Walker or Goddard, respectively. The first person to describe a new species (and publish the name) becomes the author of that scientific name and that person’s name is often cited with the arthropod, e.g., Phlebotomus diabolicus Hall. If subsequently the species is moved to another genus through some kind of taxonomic revision, the author’s name is retained but in parenthesis — Lutzomyia diabolica (Hall). If two species are subsequently determined to be the same species (things like this happen all the time), the oldest described species — first published one — becomes the official name. The other name is then considered a synonym and goes away. Governing all this is the standard code of rules of nomenclature that has been laid down by the International Commission on Zoological Nomenclature.

MORPHOLOGICAL CHARACTERISTICS. There is tremendous variety among the arthropods, but identification of the major groups is not difficult if one is familiar with their general morphology. In fact, it is rarely necessary to use a microscope to separate the classes of Arthropoda (insects, spiders, scorpions, etc.). Table 1, above, presents a summary of the key characteristics of these classes.

On the other hand, more specific identification of specimens beyond the "class" can be difficult without aid of proper literature and, perhaps, special training. Identification to the species level often must be done by specialists who conduct taxonomic research with that particular group. For outside help with identifications, try a local university entomology department (usually at land grant universities), a military base (the U.S. Army and Navy employ more than 100 professional entomologists) or the entomology department of the Smithsonian Institution.

Insects. Like all arthropods, insects possess a segmented body and jointed appendages. Beyond that, however, there is tremendous variation: long legs, short legs; four wings, two wings, no wings; biting mouthparts, sucking mouthparts; soft bodies, hard bodies; etc. Compounding identification problems, immature forms of most insects look nothing like adults. Despite the diversity, adults can at once be recognized as insects by having six legs and three body regions or tagmata: head, thorax (bearing legs and wings if present) and abdomen (see figure 1 on page 62). No other arthropods have wings. However, some insect groups never may have had wings or have lost them through adaptation. In particular, several medically important species are wingless (lice, fleas).

Identification of immature insects presents entirely different problems. In those insects that have simple metamorphosis (grasshoppers, lice, true bugs), the imma-tures (called nymphs) look like the adults, get larger at each molt and develop wings (if present) during later molts. Identifying nymphs as insects and placing them in their proper orders is generally not a problem. However, in those groups with complete metamorphosis (beetles, flies, bees and wasps, moths and butterflies, fleas, etc.), the immature stage or larva looks nothing like the adult.

Often, the larva is worm-like and may be in water, as is the case with mosquitoes (see figure 2 above left). The three body regions are never as distinct as they are in adults, but generally the six walking legs are evident, although they are often extremely short. Fly larvae (maggots) lack walking legs and, although some (such as mosquitoes) have three body regions, others (such as house flies, blow flies, etc.) have no differentiated areas. Caterpillars and similar larvae often appear to have legs on some abdominal segments. Close examination of these abdominal "legs" (prolegs) reveals that they are unsegmented fleshy projections, with or without a series of small hooks (crochets) on the plantar surface and structurally quite unlike the six segmented walking legs on the first three body segments behind the head.

Spiders. Spiders have two body regions and eight legs (see figure 3 on page 64). The two body regions — an anterior cephalothorax and posterior abdomen — are connected by a waist-like pedicel. The former bears head and thorax structures, including eight walking legs, generally eight simple eyes on the anterior dorsal surface and mouthparts. The mouthparts, called chelicerae, are generally fang-like and are used to inject poison into prey, all spiders being predaceous. Located between the chelicerae and the first pair of walking legs are a pair of short leg-like structures called pedipalpi that are used to hold and manipulate prey. Pedipalpi may be modified into copulatory organs in males. The abdomen is usually unsegmented and bears spinnerets for web production at the posterior end. Immatures look the same as adults, except smaller.

Harvestmen or daddy longlegs (order Opiliones), have many characteristics in common with true spiders; however, they differ in that the abdomen is segmented and is broadly joined to the cephalothorax (not petiolate). Most species have extremely long, slender legs.

Mites and Ticks. These small arachnids characteristically have only one apparent body region and eight legs. The single body region (cephalothorax and abdomen fused) gives them an overall globose or disk-shaped appearance in most instances. This general appearance quickly separates the Acari from other arthropods. The body may be segmented or unsegmented with the eight walking legs present in adults. Larvae, the stage just out of eggs, have only six (rarely, fewer) legs, but their single body region readily separates them from insects. They attain their fourth pair of legs at the first molt and hereafter are called nymphs until they become adults.

As in spiders, immature ticks and mites are generally similar in appearance to adults. In general, ticks are considerably larger than mites. Adult ticks are generally pea-sized; mites are about the size of a grain of sand (often even smaller).

Scorpions. Scorpions have eight legs and an anterior broad, flat area with a posterior "tail" with a terminal sting (see figure 4 above). Although these outward divisions do not correspond with actual lines of tagmatization, they do provide an appearance sufficient to distinguish these arthropods from most others. Like spiders, the mouthparts are chelicerae and the first elongate appendages are pedipalpi. The pedipalpi are modified into pincers and are used in prey capture and manipulation. Immatures are similar to adults in general body form.

Centipedes and Millipedes. Centipedes and millipedes bear little resemblance to the other arthropods previously discussed. They have hardened, elongated "worm-like" bodies with distinct heads and many pairs of walking legs (see figure 5 above). Centipedes — often commonly called "hundred leggers" — are swift-moving predatory organisms with one pair of long legs on each body segment behind the head. Millipedes ("thousand leggers"), on the other hand, are slow-moving omnivores or scavengers that have two pairs of short legs on each body segment (after the first three segments which only have one pair each). Immatures are similar to the adults.

OTHER HELP. Several reference books about arthropod identification are available. Color is sometimes used to help in identification, but it is not always the best character.

For example, flies in the family Calliphoridae are typically shiny green, blue or copper, but there are shiny green flies in other families that are not blow flies. So, sometimes color will get you in trouble. It’s better to make identifications by examining fixed morphologic characters on the specimen. For example, beetles with the pronotum (a portion of top of thorax) clearly narrower than the head are blister beetles, family Meloidae (see an example in figure 1 on page 62). In some reference books, identification of a particular bug to place it in its correct class order, family, genus or species is achieved by finding the answers to a paired series of questions set out in the form of keys.

Most keys are dichotomous, giving the reader two choices in each couplet and the reader is then referred to another couplet depending upon the answer. This flow chart of sorts continues until an identification is reached. Some keys have good pictures and illustrations to aid in the identification while others have nothing but written descriptions. For example, a key couplet might refer the reader to look at the wing of an insect and compare it to a line drawing of several variations of wings. (Visit www.pctonline.com and click on "Current Issue Online Extras" for a pictorial key to arachnids.)

CONCLUSIONS. Many arthropods do not present a major identification problem for pest control personnel. For example, just about any PCO or technician can tell a German cockroach from an American cockroach. However, identifying certain ants, wood-infesting beetles or stored product pests may be a nightmare. It helps to break the process down into smaller — more manageable — steps. A PCO familiar with basic morphologic characteristics of each group can quickly place the specimen into a major "class" or group. For example, one would know instantly that a "stinging bug" with four clear wings must be an insect (no other arthropods have wings) and cannot be a fly, beetle or butterfly/moth. Flies have two wings, beetles don’t sting and butterflies and moths have no stinging adult members.

Knowing how to "key out" a specimen is essential for those who are consistently asked to provide identifications. Proper documentation is important, especially since many cases involve lawsuits. Pest control personnel are encouraged to take any opportunity available to increase their knowledge of entomology and particularly, identification — things like reading key textbooks or attending courses, symposia and other training events. Just as is the case with microbial agents, treatment or control recommendations for arthropods hinges on a correct identification.

The author is a medical entomologist for the Mississippi Department of Health, Jackson, Miss. He can be reached via e-mail at jgoddard@giemedia.com.

LEGAL ISSUES
In the last decade there has been a tremendous increase in litigation regarding insects, mites and ticks — especially cases from specimens found in motels, health-care facilities, expensive furniture and food products. There are lawsuits from people finding a bug in their candy bar or getting tick-borne illnesses such as Lyme disease and from people who received fire ant stings while visiting the city park. Due to this increase in litigation, proper documentation and record keeping are necessary since many insect samples become integral parts of lawsuits. In any cases of insects found in “sensitive” situations, pest control personnel should assume a lawsuit is forthcoming and act accordingly. It may be helpful to take the following steps:

1. Make a careful identification or submit the specimen to a specialist for that particular group of arthropod.

2. Document all aspects of the sample (who, what, when, where). If a food product is involved, include the lot number.

3. Use an ink pen and a bound logbook with consecutively numbered pages for all documentation. (It’s more difficult to argue that someone tampered with the data).

4. Retain the specimens in alcohol or in a freezer for at least one year.

5. Do not stray beyond your area of expertise. Don’t comment on the life cycle, ecology or health effects of a particular insect unless you are reasonably sure of the facts. Such speculation could come back to haunt you.