Ecdysteroid Responses of Estuarine Crustaceans Exposed Through Complete Larval Development to Juvenile Hormone Agonist Insecticides

Abstract

Fenoxycarb and pyriproxyfen are insecticides that gain their toxicity by specifically acting as insect juvenile hormone agonists (JHA), and so are endocrine disruptors by design and effectively prevent larvae from maturing into adults. Efforts to assess the environmental effects of JHAs on nontarget populations of invertebrates have resulted in the utilization of several established estuarine crustacean models. This work was conducted to test the hypothesis that the mortality, inhibition of development and decreased fecundity reported previously in these animals from JHA exposure coincides with abnormal circulating titers of ecdysteroids. Gravid female grass shrimp (Palaemonetes pugio) and mud crabs (Rhithropanopeus harrisii), species with different developmental plasticity and JHA tolerances, were collected and held at wet lab conditions (20 ppt salinity, 25°C) until larval release. Larvae were collected <12 hr after hatch and exposed to JHAs during a static renewal test through end of development with seawater or nominal concentrations of JHA previously shown to induce significant developmental delays and/or decreased body weights. Larvae were subsampled (10 larvae/sample, n = 2 to 8) at each developmental stage, lyophilized, and ecdysteroids extracted by homogenization in 80% methanol and elution from C18 Sep-Pak cartridges with 25%, 60% and 100% methanol to capture the polar, free, and apolar conjugates, respectively, and then quantified by ELISA. As was expected significant differences in successful completion of development (larval survival), developmental duration, and growth (dry weight) were observed. These physiological perturbations were linked with significantly altered ecdysteroid titers, supporting a newly emerging theory that juvenoids possibly act as anti-ecdysteroids through a novel molecular mechanism involving inhibition of ecdysteroid signaling.

Contributions of larval biology to crustacean research: a review

“…However, it is less understood if the same system, or a simplified version thereof, is functional also in crustacean larvae. In addition, juvenoid hormones seem to be involved in the control of larval moulting and development (Mu and Leblanc, 2004;McKenney, 2005;Tuberty and McKenney, 2005), and chemical triggers from the environment can also accelerate or delay the timing of metamorphosis, i.e. of larval moulting (see e.g., Castro, 1978; cf.…”

Ecdysteroid levels in Daphnia magna during a molt cycle: Determination by radioimmunoassay (RIA) and liquid chromatography–mass spectrometry (LC–MS)

“…Recent studies, however, suggest that methyl farnesoate is involved in the inhibition of ecdysteroid signaling, i.e. that it exhibits anti-ecdysteroid activity (Mu and LeBlanc, 2004a;Tuberty and McKenney, 2005). In insects, the ovary, the epidermis and the oenocytes are alternative sites for the synthesis of ecdysteroids (Delbecque et al, 1990).…”

“…methoprene, pyriproxyfen, fenoxycarb), have been the focus of current research (e.g. Mu and LeBlanc, 2004a;Tuberty and McKenney, 2005). A decrease in ecdysteroid levels provoked by environmental chemicals has been found to result in developmental abnormalities in Daphnia magna embryos, which suggests that ecdysteroids are indispensable for the embryogenesis of daphnids (Mu and LeBlanc, 2002).…”

Larval Biology of the CrabRhithropanopeus harrisii(Gould): A Synthesis

“…The intent of these studies was to identify concentration levels above which aquatic organisms would be adversely affected. The specific test chemicals are shown in Table 1 and include insect growth regulators Costlow, 1976, 1978;Payen and Costlow, 1977;Christensen et al, 1977aChristensen et al, , b, 1978Christensen et al, , 1984Clare et al, 1992;Celestial and McKenney, 1994;Nates-Sergio and McKenney, 2000;Cripe et al, 2003;Tuberty and McKenney, 2005;; the herbicide Alachlor (Takacs et al, 1988); the pesticides Methoxychlor (Bookhout et al, 1976), Kepone (Bookhout et al, 1980), and Mirex (Bookhout et al, 1972); components of drilling fluids (Bookhout et al, 1984a, b); polycylic aromatic hydrocarbons (Laughlin and Neff, 1979a; fuel oil (Laughlin et al, 1978); tributyltin/dibutylin compounds (Laughlin, 1983;Laughlin et al, 1983Laughlin et al, , 1984Laughlin and French, 1989c); copper (Sanders and Jenkins, 1984); cadmium (Rosenberg and Costlow, 1976); and mercury (McKenney and Costlow, 1982).…”