Changes in the mean, variance and developmental instability of morphological traits have often been used to detect environmental stress in insects. Studies have focused on linear measurements, whereas modern morphometric techniques allow the separation of shape and size effects. To examine stress effects on shape we assessed wings of Helicoverpa punctigera moths exposed to two stresses (pesticide, low temperature). The pyrethroid esfenvelerate applied in larval medium increased development time but did not affect viability, whereas low culture temperatures (7–18°C) influenced both fitness traits. Neither stress affected mean wing size, but both stresses had a marked influence on wing shape. Changes in shape were stress-specific and detectable despite moderate sample sizes. The variance in wing size was altered by low temperature stress but not pesticide exposure. Neither stress increased the asymmetry of wing shape or size; in fact cold stress decreased asymmetry for centroid size. However, measurement error of asymmetry could not be accurately assessed in these wings because scales of both wings could only be removed once. Shape changes therefore appear to be more sensitive to stress in this moth species than other morphological measures, and stress effects on variation among individuals appear to be different than those on asymmetry.
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