Insect flight is much admired by people who want to build mechanical mimics. One way to build better mimics is to better understand insect flight. The blow fly flight is complex. The up and down motion of the wings is powered by muscles that deform the thorax. The motion of the wings is modified from a straight up and down motion by smaller steering muscles. Entomologists have attempted to understand the wing movements by careful study of the muscle attachments in the static wing. However, this approach does not adequately predict the flight dynamics. A group of scientists* developed a microtomography technique for visualizing the muscles in motion. They used a particle accelerator to record X-ray images of muscles at speeds capable of making 10 images per cycle. Of interest was measuring movements of the steering muscles in coordination with the wing hinge.
The power from the deformation of the thorax can be used to help power the steering muscles. Some of the steering muscles are attached to the wing joint by tendons that have the ability to deform or buckle to accommodate wing motion. The muscle deformation was totally unexpected, but is critical to understanding wing motion. A video of the findings (embedded below) is posted on YouTube. The steering muscles are shown in green and blue. The power muscles are yellow to red. New techniques enhance our understanding of insect flight.
*Walker SM, Schwyn DA, Mokso R, Wicklein M, Müller T, et al. 2014. In Vivo Time-Resolved Microtomography Reveals the Mechanics of the Blowfly Flight Motor. In Vivo Time-Resolved Microtomography Reveals the Mechanics of the Blowfly Flight Motor. PLoS Biol 12(3): e1001823.
Photo: John Clark, UMass
Insect populations that are treated repeatedly with insecticides can develop resistance. If some individuals in a population have the ability to withstand an insecticide, those individuals will survive and pass the genes for insecticide resistance to their progeny. The insecticide resistance genes spread through the population until an insecticide can no longer effectively control a population. Insecticide resistance is present in head lice. Some head lice strains are resistant to several commonly used insecticides and are difficult to kill. Resistant lice metabolize the insecticides more rapidly or have insecticide target sites that are altered. To kill resistant head lice, a pediculicide that acts on other targets is needed.
Dimeticone is a silicone oil approved for head lice treatment in Canada and is awaiting approval in the US. The oil coats the head lice and seeps into tracheal (respiratory) system of the lice through the spiracles, blocking the exchange of oxygen and carbon dioxide. The lice die from a lack of oxygen. The treatment is effective against lice populations that are resistant to pediculicides that are neurotoxic. The dimeticone does not penetrate the skin. An 8 hour treatment is long enough to kill the lice. The dimeticone can be washed from the hair with shampoo. Some eggs may survive the treatment, and it must be reapplied after the eggs have hatched. This is a promising option for lice control.
The Northeastern US has been plagued by the invasive, Brown Marmorated Stink Bug. The Southwest US has a different invasive stink bug, Bagrada hilaris
, the Bagrada Bug. This bug is a native of Southern Africa that has become a global traveler. It is now found in Europe, Asia and North America. First noted in Los Angelos County, California, in 2008 the Bagrada bug is now in Arizona and New Mexico. The bug will feed on and damage a variety of crops but causes the most damage to crops in the cabbage family. Feeding by the bug on the central shoot will cause stunting or braching of broccoli and cauliflower resulting in multiple smaller and unmarketable heads.
Bagrada bugs will probe a variety of fruits and vegetables. Feeding sites may produce a blemish or create a site for pathogen colonization. They have been reported to devastate home gardens, especially those that do not use pesticides or take other steps to remove the bugs. Immature Bagrada bugs are brightly colored. Naive gardeners who fail to look closely have mistaken them for lady beetles. Scientists are studying the biology of the pest to try to find ways to control or manage it.
World trade has benefits, but an increase is invasive pests is not one of them.
Harlequin bug eggs
Decorative eggs are associated with Easter. Bland white chicken eggs are dyed with beautiful colors and patterns, hidden, and hunted by children or rolled on the White House lawn
. Insects have laid decorative eggs for millions of years, but have never been associated with Easter. Insect eggs come in a rainbow of colors, from pale greens to bright reds. Insect eggs can change color as they develop such as Colorado potato beetle eggs that start as a bright yellow and turn bright orange as they develop. The Harlequin bug is noted for its black and white (mod) egg patterns.
Insects have been hunting eggs long before humans evolved. Egg parasitoids seek eggs of their host, not to put in a basket, but to inject the egg with an egg of their own (an early version of the “nesting egg”). This Easter, decorative chicken eggs will draw the most attention, but insects will also “celebrate” by producing decorative eggs and engaging in egg hunts.
Blankets impregnated with pyrethroids can repel walking arthropods
Most people are familiar with the insect repellent sprays or lotions that are applied to the skin to prevent bites from mosquitoes, ticks and other biting arthropods. Advances in technology have led to increasing use of fabrics impregnated with insect repellents. One successful application is the bed net, impregnated with pyrethroids, used to prevent mosquito bites in parts of Africa and other locations that have high rates of malaria. Pyrethroids have low toxicity to humans. The formulations in the nets limit the pyrethroid transfer to the user. Pyrethroid exposure from bed net use is less than an effective skin application. At low doses, pyrethroids affect the exposed sensory receptors of arthropods causing disorientation and reduction in ability to find a host and bite.
Pyrethroid impregnated fabrics are of increasing interest to American consumers who are concerned primarily with mosquitoes, tick bites and Lyme disease. Materials that may be impregnated with pyrethroids to repel insects include hats, headbands, wrist bands, hoodies and other clothing. Manufacturers are now advertising insect repellent blankets. The insect repellent on the blanket deters walking arthropods, such as ticks, mites, chiggers, ants and other arthropods. Blankets provide a protected area to sit on in the midst of infested areas. Keep in mind that exposure to biting arthropods will be greatest when moving through a large area and arthropods such as ticks may attach to you or your clothing before you spread your blanket.
Caterpillars are adpated to rapid growth, development and continuous feeding. In the presence of predators, engaging in feeding behavior may attract predator attention and therefore not be adaptive. A group of Australian scientists* studied
the behavior of gumleaf skeletonizer caterpillars, Uraba lugens
, before and after “attacks”. The researchers “attacked” caterpillars by pinching them on the head or the abdomen, two or six times. In their experiment, the numbers of caterpillars that did not feed during the 3 hours after attack increased for the disturbed caterpillars compared to undisturbed controls. Caterpillars that were “attacked” six times were less likely to feed during the next 3 hours than those only attacked twice. The authors concluded that the caterpillars “assess the risk” of predation from and delay feeding to avoid predators.
*Petah A. Low, Clare McArthur, Dieter F. Hochuli.2014 Dealing with your past: experience of failed predation suppresses caterpillar feeding behaviour. Animal Behaviour 90:337e343
Insect taxonomists seek to delimit, describe and identify species. The tools of molecular biology can be useful in cases where species cannot be readily identified based on morphological characters. Some insects are only known from collected adults and have never been clearly associtated with an immature. The sure way to associate adults and immatures is to rear the insects from eggs and describe the immature stages. For many insects, especially many aquatic insects, eggs are difficult to obtain and immatures are difficult to rear. Adult hymenopteran parasitoids may be captured in traps but the host unknown. This complicates the process of linking adults and immatures. Immatures of some species may have multiple forms or be nondescript. Scale insect immatures start life as mobile “crawlers” but settle onto plants and secrete a waxy covering. In some cases, including agricultural pests, the scale insects cannot be identified in the immature stage. Identification requires waiting until adults emerge and identifying the adults.
DNA markers are proving useful tools in many otherwise intractible cases. A species has the same chromosomes, genes and DNA sequences as an adult as it does as an immature. A DNA sequence that is diagnostic of an adult insect is diagnostic for all stages of immatures as well. DNA markers are useful for linking immatures and adults and can speed the process of identification.