Individual and Joint Actions of Selenate and Methylmercury on the Development and Survival of Insect Detritivore Megaselia scalaris (Diptera: Phoridae)

Abstract

Abstract. Despite the important roles played by insects in most ecosystems, surprisingly little is known about how anthropogenic pollutants or their mixtures interact to affect insect populations. The independent and joint actions of selenate and methylmercury on a ubiquitous insect detritivore, Megaselia scalaris (Loew), were determined in this study. Ovipositing females did not distinguish between untreated food sources and those contaminated with toxic concentrations of selenate, methylmercury, or both chemicals in combination. Even at the highest concentrations of pollutants, no negative effects were observed for the egg stage. However, larval survival was significantly decreased and development significantly prolonged by selenate and methylmercury individually at low or intermediate ecologically relevant treatment levels. Potentiation was strongly evident because mixtures containing concentrations as little as only 1% of the respective individual median lethal tolerances (LC 50 s) caused significantly more mortality and delayed larval development than would be expected from the responses selenate and methylmercury elicit individually. However, survival and pupal development was not affected at any rate tested. Female fecundity was significantly decreased by methylmercury but not by selenate or mixture treatments. The relative toxicity to M. scalaris of each of the individual and joint treatments was selenate (LC 50 = 260 lg/g) < methylmercury (LC 50 = 22 lg/g) < the mixture at approximately 5% of the LC 50 concentration of each of the components (12 lg/g selenate plus 1.0 lg/g methylmercury). The increased mortality and delayed larval development within sites contaminated by selenate, methylmercury, or combination of the two have substantial implications for the ecology, population dynamics, and sustainability of M. scalaris populations. If these results can be extrapolated to other arthropod detritivores, ecosystem food-web function may be substantially affected.As a class, insects dominate the world in which we live. More than 70% of all known species are insects, and

Selenium Toxicity to Honey Bee (Apis mellifera L.) Pollinators: Effects on Behaviors and Survival

“…Se deters feeding in certain insect [30], [43], [44] and mammalian [45], [46] herbivores, and may reduce feeding behaviors such as PER in honey bees. However, some insects cannot detect Se and will ingest it in laboratory feeding studies [47], [34]. In our study, the presence of selenate in sucrose did not reduce the responses of honey bees to stimulation of the antennae or proboscis.…”

“…In other insect plant-feeders, selenomethionine was as toxic as selenate in S. exigua [33], but more toxic than selenate in H. virescens [60]. In the detritivore Megaselia scalaris Loew (Diptera: Phoridae), selenomethionine was more toxic than selenate [47]. In insects fed various forms of Se, selenocompounds concentrated in the hindgut of the Se-tolerant Plutella xylostella L. (Lepidoptera: Plutellidae) [62], whereas Se concentrated in the Malpighian tubules of the Se-intolerant Tenebrio molitor L. (Coleoptera: Tenebrionidae) [63], suggesting these are the sites of sequestration and detoxification.…”

Heavy Metal Pollutants and Chemical Ecology: Exploring New Frontiers

“…Synergy occurs when chemicals interact in a way that increases their joint toxicity beyond that expected if their effects were additive. Jensen et al (2006) reported an example of synergy of methylmercury and selenate in a study of effects of these chemicals on an insect detritivore (the fly Megaselia scalaris). Mixtures containing as little as the LC5 (Lethal Concentration 5%) of both chemicals resulted in 100% larval mortality.…”

The impacts of metals and metalloids on insect behavior

“…In combination, effects may not simply be additive, but possibly potentiating or antagonistic. For example, the joint toxicity of mercury and Se to an insect detritivore, the phorid fly Megasilia scalaris Loew, was strongly potentiating, with just 5% of the LC 50 ’s of the two elements combined producing significantly increased developmental time and significantly greater mortality than the LC 50 of either element alone (Jensen et al., 2006). Where available, we have included the literature that provides information on the joint effects of metals on insect behaviors.…”