DDT ban faulted for high mos­quito pop­u­la­tion

Study up­ends blam­ing warm­ing for in­creases

The Washington Times Daily - - FRONT PAGE - BY VALERIE RICHARD­SON

The U.S. mos­quito pop­u­la­tion is on the rise, but don’t blame cli­mate change. Blame the ban on the in­sec­ti­cide DDT.

A study pub­lished this week in Na­ture Com­mu­ni­ca­tions at­trib­uted the de­cay of DDT con­cen­tra­tions as well as ur­ban­iza­tion to an in­crease in mosquitoes over the past 50 years.

“Mos­quito pop­u­la­tions have in­creased as much as ten­fold, and mos­quito com­mu­ni­ties have be­come two- to four­fold richer over the last five decades,” the pa­per said. “These in­creases are cor­re­lated with the de­cay in resid­ual en­vi­ron­men­tal DDT con­cen­tra­tions and grow­ing hu­man pop­u­la­tions, but not with tem­per­a­ture.”

The anal­y­sis, con­ducted by re­searchers from Rut­gers, the Uni­ver­sity of Cal­i­for­nia, Davis and the Uni­ver­sity of Cal­i­for­nia, Santa Cruz, flies in the face of state­ments by en­vi­ron­men­tal groups link­ing warmer tem­per­a­tures to mos­quito-borne ail­ments like the West Nile and Zika viruses.

“Sur­pris­ingly, de­spite in­creases dur­ing the last

five decades, an­nual av­er­age tem­per­a­ture was non­signif­i­cant in most analy­ses for all three re­gions, and very weak in the sin­gle anal­y­sis in which it was sig­nif­i­cant, and tem­per­a­ture was never sig­nif­i­cant with­out DDT in the model,” said the study.

The re­search ex­am­ined mos­quito data go­ing back eight decades in Cal­i­for­nia, which saw a ten­fold mos­quito surge, and six decades in New Jersey and New York.

In 1972 the En­vi­ron­men­tal Pro­tec­tion Agency banned DDT amid alarm over its im­pact on mos­quito-eat­ing wildlife, par­tic­u­larly birds and rap­tors.

En­vi­ron­men­tal groups have for years warned that warmer tem­per­a­tures and in­creased rain­fall may be driv­ing mos­quito-borne dis­eases. “Cli­mate Change Bites: As tem­per­a­tures rise, mosquitoes and ticks thrive. And so do the dis­eases they carry,” said a Dec. 31 post by the Na­tional Re­sources De­fense Coun­cil.

“The links be­tween mosquitoes and tem­per­a­ture are sci­en­tif­i­cally clear, and it’s pos­si­ble that cli­mate change may now be play­ing a role in the spread of the Zika virus, a dis­ease sus­pected of caus­ing se­ri­ous birth de­fects,” said En­vi­ron­men­tal De­fense Fund cli­mate sci­en­tist Ilissa Ocko in a Feb. 18 post.

Cit­ing re­search by the Yale School of Pub­lic Health, EarthTalk re­ported that “the on­set of hu­man-in­duced global warm­ing is likely to in­crease the in­fec­tion rates of mos­quito-borne dis­eases like malaria, dengue fever and West Nile virus by cre­at­ing more mos­quito-friendly habi­tats.”

The July 2013 col­umn in E: The En­vi­ron­men­tal Mag­a­zine was head­lined, “Mos­quito-borne ill­nesses on the uptick — thanks to global warm­ing.”

In the lat­est study, how­ever, sci­en­tists said that pre­vi­ous re­search failed to take into ac­count the im­pact of DDT and land use.

“Although many stud­ies have found pos­i­tive cor­re­la­tions be­tween tem­per­a­ture and in­sect pop­u­la­tions, most have been lim­ited in tem­po­ral scope to the past five decades and nearly all of these stud­ies have ig­nored the in­flu­ence of land use or an­thro­pogenic chem­i­cal use,” said the pa­per.

The study also said that pop­u­la­tion growth had re­sulted in mosquitoes ex­pand­ing their habi­tat to ur­ban ar­eas.

“While our cor­rel­a­tive analy­ses sug­gested that DDT was the strong­est driver of mos­quito pop­u­la­tions over­all, other fac­tors, such as land use, that have changed mono­ton­i­cally over the last cen­tury, were also im­por­tant in ex­plain­ing pat­terns of change in mos­quito com­mu­ni­ties,” the pa­per said.

In­ter­na­tional de­bate over the use of DDT has raged for decades. In 2006 the World Health Or­ga­ni­za­tion (WHO) re­versed its 30-year phase-out of the in­sec­ti­cide by rec­om­mend­ing in­door spray­ing in African na­tions be­set by epi­demics of malaria, a po­ten­tially deadly mos­quito-borne dis­ease.

In 2015 WHO re­ported an es­ti­mated 214 mil­lion cases of malaria and 438,000 deaths, about 90 per­cent of those in sub-Sa­ha­ran Africa.

The Cen­ters for Dis­ease Con­trol and Pre­ven­tion re­ported 43,937 cases of West Nile virus from 1999 to 2015, with 1,911 deaths. This year, as of Dec. 6, 1,622 cases have been found in 47 states, re­sult­ing in 84 deaths.

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