Muscles And Locomotion

the recovery stroke is relatively slow. Accordingly, the retractor muscles are well developed 451

compared with the protractor muscles.

In the best swimmers other important structural changes can be seen, such as streamlining of the body and restriction of movement and/or change in position of the coxa. In adult Dytiscus, for example, which may reach speeds of 100 cm/sec when pursuing prey, the coxa is inserted more posteriorly than in terrestrial beetles and is fused to the thorax. Thus, the fulcrum for the rowing action is the dicondylic coxotrochanteral joint which operates like a hinge so that the leg moves only in one plane. Because of this arrangement, all of the muscle power can be used to effect motion in this plane (Ribera et al., 1997).

Several variations are found in the rhythms of leg movements. Where a single pair of legs is used in swimming, both legs retract together. When both the midlegs and hindlegs are used, both members of the same body segment usually move simultaneously, but are in opposite phase with the legs of the other segment; that is, when one pair is being retracted, the other pair is being protracted. In adult Haliplidae and Hydrophilidae and many larval beetles all three pairs of legs are used, in a manner comparable with the tripodal gait of terrestrial insects.

Steering in the horizontal plane (control of yawing) is achieved by varying the power exerted by the legs on each side. For vertical steering (movement up or down) the nonpropulsive legs become involved. These may be held out from the body in the manner of a rudder or may act as weakly beating oars. By varying the angle to the body at which the legs are placed the insect will either dive, surface, or move horizontally through the water. Most aquatic insects are quite stable in the rolling and pitching planes because of their dorsoventrally flattened body. (See Figure 14.14 for explanation of the terms yawing, pitching, and rolling.)

3.2.3. Swimming by Other Means

A variety of other methods for moving through water can be found in insects, including body curling and somersaulting found in many larval and pupal Diptera, body undulation (larval Ephemeroptera and Zygoptera), jet propulsion (larval Anisoptera), and flying (a few adult Lepidoptera and Hymenoptera) (Nachtigall, 1974).

Many midge and mosquito larvae rapidly coil the body sideways, first in one direction, then the other, to achieve a relatively inefficient form of locomotion. Chironomids, for example, lose 92% of the energy expended in the power stroke during recovery. Consequently, a 5.5-mm larva oscillating its body 10 times per second moves at only 1.7 mm/sec through the water. Mosquito larvae possess flattened groups of hairs (swimming fans) or solid "paddles" at the tip of the abdomen and are consequently more efficient and more active swimmers than chironomids.

Pupae of midges and mosquitoes somersault through the water, especially when attempting to escape predators. Interestingly, the surface-dwelling pupa of the mosquito Culex pipiens somersaults at a greater frequency (hence swims faster) than the bottom-dwelling pupa of the midge Chironomus plumosus, perhaps because there is greater predator pressure for a surface-dweller (Brackenbury, 2000).

Larvae of Zygoptera and some Ephemeroptera undulate the abdomen, which is equipped at its tip with three flattened lamellae (Zygoptera, Figure 6.11) or swimming fans (Ephemeroptera, Figure 6.4). Some ephemeropteran larvae supplement the action of the fans by rapidly folding their abdominal gills against the body.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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