Hexapoda 2 (insects)

The Apterygote (wingless) insects

These are the Diplura (bristletails), Collembola (springtails), Protura and Thysanura (silverfish).

The bristletails and silverfish both have two long cerci, and between this a caudal appendage. There are just under 10,000 described species of Apterygotes.

Class Pterygota (winged) insects

These insects have two pairs of wings; one pair on the mesothorax and another on the metathorax. Pterygotes have muscles which allow them to close their spiracles so greatly reducing water loss and enabling them to colonize drier habitats.

The Pterygotes can be further divided into two groups; those that undergo complete metamorphosis (holometabolous), and those that undergo gradual metamorphosis (hemimetabolous).

Cimex lectularius, bed bug

Hemimetabolous insects have young that resemble the adults, and the gradual development of wings is external . Such insects include, Cimex lectularius (the bed bug) above, which shows the gradual change to the adult form, also Odonata (dragonflies), Orthoptera (grasshoppers), Dermaptera (earwigs) and Hemiptera (aphids, cicadas).

A typical holometabolous insect the brown house moth, Hofmannophila pseudospretella shown on the below in the various stages of its life.

Hofmannophila speudospretella, brown house moth

Holometabolous insects have young (larva) that usually do not resemble the adult (see above), and often occupy a different niche. These insects form a pupa (see above) before emerging as the adult form.

About 88% of the described insects are holometabolous and include the four largest Orders that have diversified along with the diversification and radiation of the Angiosperms; they are the Diptera (flies), Coleoptera (beetles), Hymenoptera (wasps, ants, bees), and Lepidoptera (butterflies and moths).

Insects as vectors of diseases in humans

Disease Insect vector
Malaria Anopheles mosquito (Diptera)
Yellow fever Aedes aegypti Mosquito (Diptera)
Filariasis Culex mosquito (Diptera)
Typhoid House fly (Diptera)
Dengue Aedes mosquito (Diptera)
Sleeping sickness Tsetse fly (Diptera)
Plague Fleas (Siphonaptera)
Typhus fever Louse (Anoplura/Siphunculata)
Chagas Rhodnius (Hemiptera)

Insects as pollinators.

Importance of insects

Insect behaviour patterns.

Courtship. This usually involves males trying to attract females. The female behaviour is simply to accept or reject, e.g. during courtship the male scorpion fly presents the female with a dead insect which she eats during copulation.

Copulation. Copulation is the physical joining of the male and female culminating in the passing of sperm from the male to the female, e.g. bumblebees.

Egg-laying. Most species have very specific site requirements for egg-laying, so that the eggs are laid on, in or near the source of food for the larva or nymph, e.g. dung beetles.

Defence. Defence can be active, e.g. sting (bees, wasps, etc.), bite (beetles, etc.), chemicals (bombardier beetle); or passive e.g. hiding (cockroach), camouflage (stick insect).

Communication. Communication is the transfer of information between individuals - usually of the same species, e.g. honeybees communicating the location of a good food source.

Grooming. This is especially important in hairy insects, e.g. bumblebees. These and all others need to keep their antennae, eyes, wings, legs and mouthparts clean. Most have a brush or comb on their forelegs, e.g. bumblebees, that can be used to cleans antennae and legs.

Insect records

Fastest flight
Austrophlebia costalis
(Odonata: Aeshnidae), a dragonfly at 98 km/h
Hybomitra hinei wrighti (Diptera: Tabanidae), a fly at 145 km/h
Fastest wing beat
Forcipomyia sp. (Diptera:Ceratopogonidae), a midge, species not known can beat its wings 1046 times per second.
Fastest runner
Cicindela hudsoni, an Australian tiger beetle can run at 2.5 metres per second.
Least specific vertebrate blood sucker
Glossina palpalis
(Diptera: Glossinidae), tsetse fly. It can feed on any vertebrate.
Longest
Pharnacia serratipes
, a stick insect, at 55.5 cm (22 in).
Smallest adult
Dicopomorpha echmepterygis
(Hymenoptera: Mymaridae), a parasitic wasp. The length of the male is 139 µm.
Largest swarm
Schistocerca gregaria
, the desert locust. In 1954 a swarm covering 200 km sq invaded Kenya. The swarm was estimated to contain 10 billion individuals.
Largest eggs
Xylocopa auripennis, a carpenter bee lays eggs 16.5 mm long and 3.0 mm in diameter.
Heat tolerant
Cataglyphis bicolor
(Hymenoptera: Formicidae), a Saharan ant which can forage at body temperature above 50oC and surface temperature of up to 70oC.
Cold tolerant
Polypedilum vanderplanki
(Diptera), an African chironomid (midge) can survive submersion in liquid helium at -270oC.
Most spectacular mating
Apis mellifera
(Hymenoptera), the honey bee. The drone (male) dies after mating once. The queen bee files off with his phallus still in her vagina. The phallus having broken off after sperm exits explosively. The queen eventually ejects the phallus and goes on to mate again.
Longest regular migration
Danaus plexippus
(Lepidoptera: Danaidae), the monarch butterfly. Some migrate more than 4000 km from Southern Canada to Central Mexico. It now looks likely that the longest migration is by dragonflies who make a 14 000 - 18 000 km round trip from India to southern Africa stopping off at the Maldives and the Seychelles.
Longest adult life
Lasius niger, ant queen survived 28.75 years in captivity.
Pogonomyrmex owyheei, ant queen, 30 estimated in the wild.
Longest life cycle
Buprestis aurulenta larva, a wood boring beetle, emerged after 51 years
Shortest adult life
Dolania americana (Ephemeroptera), a mayfly, lives for less than five minutes after her final molt. During the five minutes she chooses a mate, mates, and lays her eggs.
Shortest generation time
Rhopalosiphum prunifolia
, an aphid, has the shortest generation time of 4.7 days at 25o C.
Most polyandrous (female with highest number of mates)
Apis dorsata
(Hymenoptera:Apidae) a queen bee mated 53 times, each with a different male.
Chrysochus cobaltinus (Coleoptera: Chrysomelidae), a blue milkweed butterfly female, had up to 60 matings, though some of these were multiple matings with the same male.
Loudest
Brevisana brevis (Homoptera: Cicadidae), a cicada, produces a calling song with a mean sound pressure level of 106.7 decibels at a distance of 50 cm.
Best "new" man
Male Nicrophorus orbicollis, a burying beetle, participate in all activities, remain with the brood throughout development, and can take over all parenting responsibilities if the female disappears.
The above insect records, taken from Walker, T.J., ed. 2001. University of Florida Book of Insect Records, 2001.
Fastest muscles
Termes panamensis
, (a termite) has the fastest muscles in the world. It needed film shot at 40,000 frames per second to calculate the speed at which T. panamensis snaps its jaws shut, and the result is 70.4 m s-1. Its jaw muscles are so big that they fill half the space inside its head, and they are triggered by seeing an intruder's face inside the nest.
Longest sexual intercourse
In many stick insect species males are never or hardly ever seen, however in other species the males can maintain intercourse for months at a time.

Flight data from some insects

Insect Speed m/s Wing beats/s
Scorpion fly 0.5 28
Field grasshopper 0.5  
Mosquito 0.9  
Damselfly 1.5 16
Stag beetle 1.5  
Ammophila wasp 1.5  
House fly 2.0 190
Common wasp 2.5  
Large white butterfly 2.5 12
Honey bee 2.5 250
Monarch butterfly 2.8  
Bumblebee 3.0-4.5 125-240
Cockchafer 3.0 46
Hoverfly 3.5 120
Horse fly 4.0 96
Desert locust 4.4  
Hummingbird hawk moth 5.0 85
Hornet 6.0 100
Dragonfly 7.0 38
Fruit fly (Drosophila)   300
Midge (Scottish)   >1000
German wasp, Vespula germanica   250
Swallowtail butterfly   5

4 main functions of a sense of smell in insects, plus examples

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