Life history strategies of the spider mite, Tetranychus ludeni Zacher, in response to environmental conditions : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Entomology at Massey University, Manawatu, New Zealand
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Date
2022
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Massey University
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Abstract
Tetranychus ludeni Zacher (Acari: Tetranychidae) is an invasive pest of many horticultural crops and now occurs in all continents except Antarctic. Its invasive nature and pest status have stimulated the need for understanding the plasticity of its life history strategies under different environmental conditions. So far, little is known about effects of environmental factors on the life history traits in T. ludeni. In this thesis, I investigated its life history strategies in response to temperature, food deprivation, and predator threat. I show that life history traits of T. ludeni were highly flexible and adaptive to dynamic thermal environment. Higher temperature accelerated development but reduced adult body size and longevity. Increasing temperature elevated the intrinsic rate of increase (rm) but shortened generation time (T) and the time to double the population size (Dt). The net population growth rate (R0) was higher at 20 and 25ºC compared to lower and higher temperatures. Thermotolerance in T. ludeni was stage-dependent with eggs being the most vulnerable and adults the most tolerant. No eggs hatched after exposed to 45°C for ≥ 15 hours, 48°C for ≥ 12 hours, or 51°C for three hours; no adults survived 51°C or 54°C for ≥12 hours or 57°C for ≥ six hours, and heat tolerance of other life stages fell in between. Intermittent fasting (IF) had sex-specific and mating status-specific effects on the lifespan of T. ludeni. It extended the lifespan of females regardless of mating status but shortened that of mated males and had no effect on virgin males. IF reduced fecundity and egg size and extended offspring developmental time. My study indicates that predator-induced fears significantly lowered the fitness of T. ludeni. Cues from predators and injured prey shortened the longevity by 23–25% and oviposition period by 35–40% and reduced the fecundity by 31–37% in T. ludeni females. These cues significantly reduced intrinsic rate of increase (rm) and net population growth rate (R0), and extended time to double the population size (Dt). Findings from this study contribute to our understanding of the effects of environmental stressors on life history traits in T. ludeni, providing knowledge for pest risk analysis and development of pest management programs.
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Tetranychus, Effect of temperature on, Food, Predators of