Reproducing during Heat Waves: Influence of Juvenile and Adult Environment on Fecundity of a Pest Mite and Its Predator

Abstract

The thermal history of arthropod predators and their prey may affect their reproductive performance during heat waves. Thus, a matching juvenile and adult environment should be beneficial as it enables the individuals to acclimate to extreme conditions. Prey fecundity, however, is also affected by a second stressor, namely predation risk. Here, we assessed the impact of extreme and mild heat waves on the reproductive output of acclimated (juvenile and adult heat wave conditions are matching) and non-acclimated females of the biocontrol agent Phytoseiulus persimilis, a predatory mite, and its herbivorous prey, the two-spotted spider mite Tetranychus urticae, on bean leaves. Their escape and oviposition rates and egg sizes were recorded over 10 days. Additionally, ovipositing prey females were exposed to predator cues and heat waves. Acclimation changed the escape rates and egg sizes of both species, whereas fecundity was only influenced by the adult thermal environment via increased egg numbers under extreme heat waves. Acclimation reduced predator and prey escape rates, which were higher for the predator. Pooled over acclimation, both species deposited more but smaller eggs under extreme heat waves. Acclimation dampened this effect in prey eggs, whereas acclimation resulted in smaller female eggs of the predator. Prey deposited larger male and female eggs. Predator cues reduced prey oviposition, but the effect was small compared to the large increase gained under extreme heat waves. We argue that the success of predators in controlling spider mites during heat waves mainly depends on the fates of escaping predators. A permanent absence of predators may result in the numerical dominance of prey.

Parental exposure to heat waves improves offspring reproductive investment in Tetranychus urticae (Acari: Tetranychidae), but not in its predator, Phytoseiulus persimilis (Acari: Phytoseiidae)

“…Consequently, it was assumed that their average age during the first day of an experiment was 3.5 days and 12.5 days during the last day. The predation rate at age t (denoted P ( t )) was modeled by means of a generic non‐linear model (see Tscholl et al., 2023) given as$$$$ y(t)=a{t}^b{e}^{ct+d{t}^2} $$$$where y ( t ) denotes a given trait value at age t (e.g. y ( t ) = P ( t )).…”

“…Second, based on life history theory, heat stress may directly induce flexible shifts in egg number and/or egg size in reproducing females in order to maximize their own lifetime reproductive output (Roff, 1992; Stearns, 1992). Commonly, more of the finite energy for reproduction is allocated to the number of eggs, but not their size, when females are exposed to heat stress [e.g., geckos (Starostová et al., 2012), mites (Tscholl et al., 2023)]. A potential cause could be that high temperatures result in faster juvenile growth and earlier adulthood, thereby increasing juvenile survival and population growth.…”

“…The predator is specialized to feed on spider mites and is used as a very successful natural enemy in several crop systems, both in the field and in greenhouses, to control T. urticae (Mcmurtry & Croft, 1997 ). Both mite species are characterized as income breeders with fast juvenile development (4–10 days), small adult body sizes (300–500 μm body length), sexual size dimorphism (smaller males), finite growth (Crooker, 1985 ; Sabelis, 1985b ), and high reproductive output (up to 80 eggs/female predator and 160 eggs/female prey) under optimal conditions (Lü et al., 2019 ; Tscholl et al., 2022 , 2023 ; Walzer et al., 2022 ; Wrensch & Young, 1975 ). A single mating is sufficient for life‐time reproduction of both species (Lü et al., 2019 ; Walzer & Schausberger, 2014 ), which can last up to 30 days (Li & Zhang, 2018 ; Walzer & Schausberger, 2014 ).…”

“…A single mating is sufficient for life‐time reproduction of both species (Lü et al., 2019 ; Walzer & Schausberger, 2014 ), which can last up to 30 days (Li & Zhang, 2018 ; Walzer & Schausberger, 2014 ). Female offspring are numerically dominant under optimal conditions, but the sex‐ratio may shift to become more equal or even male‐biased under harsh conditions (Margolies & Wrensch, 1996 ; Tscholl et al., 2023 ; Walzer & Schausberger, 2014 , 2015 ). Both species inhabit mainly the top parts of plants, where they are exposed to fluctuating daily and seasonal environmental conditions (Walzer et al., 2022 ).…”

“…Exposed to mild (daily maximum temperature = 32°C) and extreme (daily maximum temperature = 38°C) heat wave conditions, both species increased their reproductive output at the cost of smaller eggs. Juvenile thermal acclimation extenuated this effect on egg sizes of prey, whereas the opposite was the case in female predator eggs (Tscholl et al., 2023 ). However, the potential effects of heat wave‐experienced parents on the reproductive output of their offspring under heat waves have not yet been evaluated for P. persimilis and T. urticae .…”