P&PDL Picture of the Week for
December 5, 2005

“Nit Picking”

Timothy J. Gibb, Insect Diagnostician, Department of Entomology, Purdue University

The following picture of the week shows the development of head lice on the shafts of human hair.  Many questions arise every year concerning head lice and children. Typically, the presence of head lice elicits a frenzy of spraying, cleaning, laundering and other activities by parent teachers and school staff. I am much more concerned about the negative health effects of indiscriminate pesticide spraying in busses, homes or classrooms than I am about head lice.  The fact that head lice cannot survive off a host for more than a few hours, casts huge doubts about the effectiveness of bus sprays.  I would not recommend them at all.

There is a lot of talk about insecticide resistance in head lice, however, there is much less documented evidence.  I personally think it is over rated.  Head lice are difficult to control and easy to spread, thus reinfestation is usually what accounts for people’s perception of resistance.

Permethrin, pyrethrin, malathion and Lindane are all chemicals that can be used.  Chances of any insect becoming resistant to all of these products at once is just about zero.  Rotating pesticides is the best way to ensure that resistance does not occur.

Using mechanical measures (combs and thorough inspections) in conjunction with chemical treatments is really the best solution.  Washing personal items (combs, hats etc) also may help to some degree. 

Other products (like Debug) are based on little scientific information.  The thought is that the enzymes render the hair much more difficult for a louse to lay its eggs on or for the nits to stick to the hair shafts (dissolves the glue material nit needs to stick).

Again, the scientific testing in most of these products is not complete enough to say whether they will or will not work.

Click image to enlarge

head lice

head lice

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service