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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Lousy times: Human head louse, Pediculus humanus capitis, and human body louse, Pediculus humanus humanus

 

Human body lice diverged from their head inhabiting kin when fabric and fur replaced bare skin as the predominant fashion.

 

First, as promised: Winners of the 2016 Bug of the Week Academy Awards

Last week was fun and games at the. Bug of the Week thanks the members of the Bug of the Week Academy for selecting this year’s winners.

In the category “GLAD THEY ARE TINY” the runaway winner was the lycosid wolf spider in ““Wolves on a summer’s night” for her stunning vampire-like performance as the exsanguinator of crickets.

In the category "YOU OUGHT TO BE IN PICTURES" a close race was won by dame Danaus plexippus in the role of a peripatetic vagabond who braves lethal predators, crazed New England drivers, and horrific weather on a three thousand mile journey to her winter home in Mexico in “Monarchs and Mojitos.”

In the category "MORE THAN I NEEDED TO KNOW" the tiny black fly pulled an upset for her sanguine performance in “There will be blood.”

Congratulations to this year’s stand-out winners!

Lousy times

Scores of lice eggs, a.k.a nits, can be found in clothing of those infested with body lice.

A few weeks ago we visited yellow fever mosquitoes and the Zika virus. This week we turn our attention to another blood sucker in the news. Human head lice have been making headlines in recent weeks owing to the discovery that infestations of these unpleasant buggers may be on the rise. As a child growing up in rural New Jersey, the first day back to elementary school was punctuated with a distressing trip to the school nurse for the annual head louse inspection. In my school the nurse was a formidable woman with very large hands, a deep voice, and the aroma of a hint of disinfectant.  She would plunge her finger tips into each child’s scalp in search of nits, the tiny white eggs of the head louse. Nits are deposited by the female head louse, who firmly glues the eggs to hairs with a proteinaceous glandular secretion. Eggs hatch into tiny nymphs with needle-like mouthparts that are inserted into the skin to imbibe protein rich blood coursing through capillaries below the surface. Nymphs shed their skin several times before developing into blood thirsty adults that breed within the hirsute forest. 

For boys in my household, detection of nits or head lice earned a marine-style haircut when Dad arrived home that evening. Girls were treated a tad better but had to endure several lindane shampoos to rid themselves of these ectoparasites. With modern advances in insecticide chemistry lindane was supplanted by natural and synthetic derivatives of the botanical insecticides known as pyrethrins. Pyrethrins and their chemical children, called synthetic pyrethroids, disrupt normal nerve function in insects.

So, why are head lice on the rise? In a recent study, scientists at the University of Massachusetts and their colleagues discovered that head lice carried genes for resistance to pyrethrins and permethrin-based insecticides in more than 99% of humans sampled. This sample was robust in that 115 subjects from 18 geographical locations in 12 U.S. states provided head lice for the study. Samples of head lice from several locations in Canada revealed high levels of insecticide resistance as well. One disturbing trend discovered in the study was the mutation conferring insecticide resistance had increased dramatically in the U.S. in samples of lice collected between 1999 and 2008. The widespread use of popular pyrethrins and pyrethroids appear to have selected for highly resistant “super lice” that are very difficult to control with these insecticides. Fortunately, alternative chemistries are available to combat these tiny vampires.

 

 

A busy digestive tract is a sure sign that this little louse enjoys nutritious Bug Guy blood.

Before we leave the topic of head lice, here is one more tidbit about head lice and their closest kin, body lice, that is pretty cool. Recent genetic studies revealed that the lineage leading to body lice diverged from their cousins the head lice some 80,000 to 170,000 years ago. As the name implies, head lice live on the head and perish quickly if they stray from this furry domain. Body lice occupy clothing and sneak onto human skin only to obtain their obligatory blood meals. Using the timing of this divergence as a metric, scientists believe that humans must have begun wearing clothing sometime around 80 to 170 thousand years ago. By donning clothes, a new niche was created and a new evolutionary trajectory for an ancient human pest was launched.

References

Two interesting articles “Knockdown Resistance Allele Frequencies in North American Head Louse (Anoplura: Pediculidae) Populations” by Kyong Sup Yoon, Domenic J. Previte, Hilliary E. Hodgdon, Bryan C. Poole, Deok Ho Kwon, Gamal E. Abo El-Ghar, Si Hyeock Lee, and J. Marshall Clark; and “Origin of Clothing Lice Indicates Early Clothing Use by Anatomically Modern Humans in Africa” by Melissa A. Toups, Andrew Kitchen, Jessica E. Light and David L. Reed, were used to prepare this episode.