A comparison of the effects of organophosphate insecticide exposure and temperature stress on fluctuating asymmetry and life history traits in Culex quinquefasciatus

doi:10.1016/S0045-6535(01)00140-0

Chemosphere

Volume 45, Issues 6–7, November 2001, Pages 713-720

https://doi.org/10.1016/S0045-6535(01)00140-0 Get rights and content

Abstract

Effects of exposure to a non-chemical (temperature) or chemical (organophosphate insecticide) stressor during larval development were compared in Culex quinquefasciatus mosquitoes. Stress was measured in two ways: using conventional life history traits (survival, development time and a measure of body size) and by calculating the degree of developmental instability from the departure from bilateral symmetry of wing characters (fluctuating asymmetry). Increasing insecticide dose, but not temperature, was observed to elevate wing fluctuating asymmetry in male but not female mosquitoes. Insecticide treatment reduced survival and was associated with a significant reduction in wing trait sizes in both females and males but did not significantly affect development time. Temperature was associated with a significant reduction in all life history traits in both sexes. Therefore wing fluctuating asymmetry in C. quinquefasciatus cannot be used as a general biomonitor of all stress, although it may have potential as a more specific monitor of chemical stress. It needs to be complimented with other measures such as life history and biochemical methods. The significant differences in response between sexes may impact on results of short-term larval exposures to insecticides.

Introduction

Environmental or genetic stress has been shown many times to cause an increase in the fluctuating asymmetry (FA) of bilaterally morphological traits (Parsons, 1990; Clarke and McKenzie, 1992; Markow, 1995). FA can be defined as the random non-directional deviation from perfect bilateral symmetry with a normal distribution around a mean of zero (Palmer and Strobeck, 1986; Møller and Swaddle, 1997). An increase in FA is interpreted as an indication of increased developmental instability or reduced developmental homeostasis (Clarke and McKenzie, 1992; Markow, 1995). Environmental stressors shown to increase FA include temperature extremes, larval density, chemical pollution and nutrition deficiency.

The present study was designed to look at the effects of a non-chemical (temperature) and chemical (insecticide) stress on the development of Culex quinquefasciatus mosquitoes (C. pipiens sp. complex) by using levels of FA and more conventional life history traits as indicators of environmental stress. Temperature is an important environmental determinant for ectothermic organisms since it affects all biological processes. Many organisms operate optimally within a very narrow temperature range and deviations from this could impose stress during development (Parsons, 1987, Parsons, 1989; Imasheva et al., 1997). At the molecular level, temperature stress directly affects biological molecules such as enzymes, which are crucial for the survival of the organism, whereas at the population level it may result in chronic effects within the genetic architecture of the population (Imasheva et al., 1997). Temperature per se is a general stressor, which impacts upon the whole developmental homeostasis of an ectothermic organism, mainly by affecting crucial biological pathways and systems pivotal to survival (Parsons, 1961). On the other hand, xenobiotic compounds are often more specific because they generally affect individual pathways within the organism (Parsons, 1990). Since these stressors have different modes of action on the organism, it is of interest to compare their effects on developmental homeostasis. Effects of exposure to these stressors on the development of the C. quinquefasciatus mosquitoes, with particular reference to phenotypic variation of life history characters such as survival of different life stages, development time, adult body size and developmental instability of fitness-related traits, were measured.

Section snippets

Insect strain

A standard insecticide susceptible laboratory strain of C. quinquefasciatus named SLab was used (Georghiou et al., 1966). The mosquitoes were reared in a constant temperature humidity room (CTH, temperature 25±0.2°C, RH 70±5%, 12:12 light to dark) using standard techniques.

Insecticide exposure

The insecticide was prepared by dissolving analytical grade temephos in ethanol. Three insecticide concentrations were prepared: 0.00011, 0.00025 and 0.00032 mg/l in 140 ml total volume of water by the addition of $100 μl$

Life history measurements

Elevated temperature significantly influenced development time measured as the mean number of days from hatching to adult eclosion (F_2,32=257,P<0.001) (Fig. 1(a)). Development time decreased as temperature increased. Exposure to temephos had no effect on development time (F_3,32=1.45,P=0.247) (Fig. 1(a)). Survival was influenced by both temperature (F_2,36=71.72,P<0.001) and insecticide dose (F_3,36=9.97,P<0.001), with highest survival at 25°C, and lowest survival at 37°C (Fig. 1(b)). No

Discussion

Insect wing lengths are routinely used in studies of developmental stability (Clarke and Ridsdill-Smith, 1990; Agnew and Koella, 1997; Crespi and Vanderkist, 1997; Hardersen and Wratten, 1998) and are thought to be adequately suited for such studies. The reason for their choice is the ease with which they can be measured and also they are usually measured with sufficient accuracy and are highly repeatable. Numerous studies correlated the level of wing FA with the degree of chemical stress due

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A comparison of the effects of organophosphate insecticide exposure and temperature stress on fluctuating asymmetry and life history traits in Culex quinquefasciatus

Abstract

Introduction

Section snippets

Insect strain

Insecticide exposure

Life history measurements

Discussion

Environ. Pollut.

Anim. Behav.

Chemosphere

Biol. J. Linn. Soc.

Anim. Behav.

Virulence parasite mode of transmission and host fluctuating asymmetry

Proc. Roy. Soc. Lond. B.

Effects of size and fluctuating asymmetry on field fitness of the parasitoid Trichogramma carverae (Hymenoptera: Trichogrammatidae)

J. Anim. Ecol.

Developmental instability analysis of Bkd-Infected spring chinook salmon Oncorhynchus tshawytscha prior to seawater exposure

Oikos

Thermally induced chronic developmental stress in coho salmon: integrating measures of mortality early growth and developmental instability