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KEY TO PRINCIPAL INSECT ORDERS

of Medical Importance

(Adults)

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By the 21st Century there have been over one_million insect species described, due to the efforts of many specialists in the 19th and 20th Centuries. Morphological differences have been the primary criteria for distinguishing species, but biological studies showing incompatibility and DNA evidence attests to the existence of exponentially more species than earlier believed. Because of their multitudes it is possible for natural selection to operate on more individuals than most other animal groups. The ability of insect populations to develop resistance to insecticides in just a few years after applications is evidence for a comparatively rapid evolution capability.

The Class Insecta is divided into two subclasses: Apterygota and Pterygota. The Apterygota include the wingless Thysanura, while all the other insects belong the Pterygota even if some of them are wingless through the process of evolution from more primitive ancestors [See: Insect Classification]. Four orders of greatest medical importance are Diptera, Hemiptera, Phthiraptera and Siphonaptera. The other orders of lesser importance include species that at times may carry pathogens or cause injury to humans and animals; they are Coleoptera, Hymenoptera, Lepidoptera and Orthoptera.

An all-inclusive key to Insecta may be found at <Insect Guide>. However, the following key includes only those orders that are of greatest medical importance to humans and animals.

1. Wings are absent _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2

Wings are present (Fig. 1, Fig. 2) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9

2. Non parasitic, free living species _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3

Ectoparasites and not free living _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5

3. The abdomen is constricted at its base. Cerci are absent (e.g. bees & wasps) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Hymenoptera

Abdomen is not constricted but rather broadly joined to the thorax. Cerci may be either present or absent _ _ _ _ _ _ _ _ _ 4

4. Mouthparts are of the biting kind. Insects are somewhat flattened and their bodies do not have scales (e.g., cockroaches) _ _ _

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Blattaria

Mouthparts have a proboscis that is coiled underneath the head. Most species have a body that is covered with scales or long

hairs (e.g., wingless moths)_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Lepidoptera

5. Mouthparts are adapted for piercing and sucking _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6

Mouthparts are used for biting (e.g., biting lice) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Mallophaga

6. The body is strongly compressed or flattened from side to side. Antennae are in grooves and visible from above. The legs are

adapted for jumping or running (e.g., fleas) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Siphonaptera

The body is not compressed but may be flattened from the top down. Antennae are not in grooves and either visible or not from

the dorsum _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7

7. The antennae are short and located in pits where they are not visible from the dorsum (e.g., louse flies) _ _ _ _ _ _ _ Diptera

Antennae are exposed and very visible _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 8

8. The tarsus has one claw that is adapted for clinging to hair (e.g., sucking lice) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Phthiraptera

The tarsus has two claws that are not adapted for clinging _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Hemiptera

9. A single pair of membranous wings is present. The hind wing pair are reduced to short halteres (e.g., mosquitoes &

stable flies) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _Diptera

Two pairs of wings are present _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10

10. The two wing pairs are different in texture and structure _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 11

The two wing pairs are similar in texture and structure _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13

11. Front wings are hard and horny without clear venation. The hind wings are thin and membranous. Mouthparts are for

chewing (e.g., beetles) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Coleoptera

The front wings are completely different from previous description _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 12

12. Front wings are like parchment with many veins. The hind wings are folded like a fan underneath the front wings.

Mouthparts are for chewing (e.g., grasshopper) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Orthoptera

The front wings are leathery at their base and membranous on the apical part (Fig. 3) Mouthparts are adapted for piercing

and sucking _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Hemiptera (Heteroptera)

13. The wings are partially covered with scales. Mouthparts are for sucking and when not feeding are coiled underneath the head

__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Lepidoptera

Wings are not covered with scales. Mouthparts are adapted for biting or sucking and never coiled underneath the head _ _ 14

14. The mouthparts are enclosed in a jointed beak that is adapted for piercing and sucking; they are also situated at the posterior

portion of the head in front of the first pair orf coxae _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _Hemiptera & Homoptera

Mouthparts are not enclosed in a jointed beak (e.g., bees & wasps)_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Hymenoptera

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Key References: <medvet.ref.htm> <Hexapoda>

Matheson, R. 1950. Medical Entomology. Comstock Publ. Co, Inc. 610 p.

Service, M. 2008. Medical Entomology For Students. Cambridge Univ. Press. 289 p

Legner, E. F. 1995. Biological control of Diptera of medical and veterinary importance. J. Vector Ecology 20(1): 59_120.

Legner, E. F. 2000. Biological control of aquatic Diptera. p. 847_870. Contributions to a Manual of Palaearctic Diptera,

Vol. 1, Science Herald, Budapest. 978 p.