If Malaria's the Problem, DDT's Not the Only Answer

In fact, pockets of resistance to DDT in some mosquito species in Africa are already well documented. There are strains of mosquitoes that can metabolize DDT into harmless byproducts and mosquitoes whose nervous systems are immune to DDT. There are even mosquitoes who avoid the toxic effects of DDT by resting between meals not on the interior walls of houses, where chemicals are sprayed, but on the exterior walls, where they don't encounter the chemical at all.

The truth is that DDT is neither superhero nor supervillain -- it's just a tool. And if entomologists have learned anything in the last half-century of dealing with the million-plus species of insects in the world, it's that there is no such thing as an all-purpose weapon when it comes to pest management. DDT may be useful in controlling malaria in some places in Africa, but it's essential to determine whether target populations are resistant; if they are, then no amount of DDT will be effective.

We have new means of determining whether populations are genetically prone to developing resistance. DDT advocates are right to suggest that DDT may be useful as a precision instrument under some circumstances, particularly considering that environmental contamination in Africa may be less of a problem than it has been in temperate ecosystems because the chemical can degrade faster due to higher temperatures, moisture levels and microbial activity. Moreover, resistance evolves due to random mutation, so there are, by chance, malaria-carrying mosquito species in Africa that remain susceptible to DDT despite more than two decades of exposure to the chemical.

But environmentalists are right to worry that the unwise use of DDT, particularly where it is likely to be ineffective, may cause environmental harm without any benefit. In 2000, I chaired a National Research Council committee that published a study titled "The Future Role of Pesticides in U.S. Agriculture." Our principal recommendation is germane to discussions of malaria management: "There is no justification for completely abandoning chemicals per se as components in the defensive toolbox used for managing pests. The committee recommends maintaining a diversity of tools for maximizing flexibility, precision, and stability of pest management."

Overselling a chemical's capacity to solve a problem can do irretrievable harm not only by raising false hopes but by delaying the use of more effective long-term methods. So let's drop the hyperbole and overblown rhetoric -- it's not what Africa needs. What's needed is a recognition of the problem's complexity and a willingness to use every available weapon to fight disease in an informed and rational way.

Author's e-mail: maybe@uiuc.edu

May Berenbaum is head of the department of entomology at the University of Illinois, Urbana-Champaign.