Malathion Influences Competition Between Aedes albopictus and Aedes japonicus

Abstract

Competitive interactions may facilitate or repel invaders into new communities, and these interactions may depend on other environmental conditions such as the presence of pesticides. Malathion is widely used in controlling agricultural pests and mosquitoes worldwide. Small amounts of malathion, previously considered inconsequential, may in fact increase in lethality when combined with biotic stressors in aquatic systems. We tested whether low concentrations of malathion (0.11 ppm) that are often detected in aquatic systems, affect competition between two invasive mosquito species Aedes albopictus (Skuse) and Aedes japonicus Theobald. There were no survivors of Ae. japonicus larvae in malathion. There was a significant negative effect of Ae. japonicus density on Ae. albopictus survival, but this effect was absent in the presence of malathion. There was also a moderate negative effect of Ae. japonicus density on Ae. albopictus female size, but this effect was absent in the presence of malathion. These findings indicate that pesticide-mediated alterations in competition and species-specific differences in susceptibility to pesticides could play a role in enhancing invasive potential of Ae. albopictus.

Interspecific Larval Competition Between Invasive Aedes japonicus and Native Aedes triseriatus (Diptera: Culicidae) and Adult Longevity

“…japonicus (Armistead et al 2008a). Similar results have been observed for other geographic populations of these two species (Kesavaraju et al 2010). Thus, these latter experiments suggested a strong competitive asymmetry among these two invasive species and suggest that competitive exclusion of Ae.…”

Pesticide-Induced Release From Competition Among Competing <I>Aedes aegypti</I> and <I>Aedes albopictus</I> (Diptera: Culicidae)

“…Substantially shorter development times to adulthood in malathion than the control treatments provides additional evidence for hypothesized release from interspeciÞc competition. These observations are consistent with studies showing condition-speciÞc interspeciÞc competition where the presence of malathion may diminish (Kesavaraju et al 2011) or accentuate (Kesavaraju et al 2010) competitive asymmetry between Ae. albopictus and other mosquitoes.…”

“…albopictus was more tolerant to malathion than Ae. japonicus, enhancing the advantage of the former species in the presence of malathion (Kesavaraju et al 2010).…”

“…The controls received 1 ml of deionized water while the treatments received 1 ml of a known concentration of malathion (Ortho-Malathion Plus, The Scotts Company, Marysville, OH) for Þnal concentrations of 0, 0.003, 0.007, 0.014, 0.028, and 0.056 mg/liter (6 treatments ϫ 3 replicates). We used similar methods as described by Kesavaraju et al (2010) to manipulate malathion concentrations. The experimental design allowed us to measure the susceptibility of mosquitoes to different doses of malathion in the presence of allochthonous resources.…”

“…In contrast, relatively few controlled studies have investigated the role of pesticides in mediating interspeciÞc competition (Kesavaraju et al 2010(Kesavaraju et al , 2011Jones et al 2011). When species have asymmetrical competitive abilities, the presence of pesticides may 1) further accentuate competitive asymmetry if the superior competitor is also least sensitive to pesticides, 2) reduce or eliminate competitive asymmetry if the superior competitor is most sensitive to pesticides, or 3) reverse the outcome of interspeciÞc competition when the presence of pesticides reverses the role each competitor has so that the superior competitor becomes the inferior competitor and vice versa.…”