Host population density and presence of predators as key factors influencing the number of gregarious parasitoid Anaphes flavipes offspring

Entomologia Exp Applicata

Skuhrovec

et al. 2019

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The parasitoid Anaphes flavipes (Foerster) (Hymenoptera: Mymaridae) is a gregarious egg parasitoid which is widely used in biological control against important crop pest beetles of the genus Oulema (Coleoptera: Chrysomelidae). Here, we present the first experimental examination of the influence of adult feeding and timing of host exposure on the longevity and fertility of this parasitoid. We confirmed a positive effect of adult feeding on longevity of both sexes. Fed parasitoids lived 3× longer than unfed ones. On the other hand, adult feeding and feeding time had no effect on female fertility. The number of hatched offspring was not increased by adult feeding, which suggests that the parasitoid emerges with already mature ovaries (proovigenic type). However, the fertility of fed females was strongly influenced by the timing of host egg exposure. By providing distinct groups of parasitoids with host eggs at different times, we were able to show lower fertility of fed females that had been offered host eggs more than 24 h after hatching. Our results thus show that the parasitoid's fertility is determined by her age at the time of parasitization rather than by feeding.

“…obs.). Moreover, the identity of the host species does not affect the size (Samková et al, ) or number of the offspring developing in one host egg (Samková et al, ).…”

Section: Methodsmentioning

confidence: 99%

Effect of adult feeding and timing of host exposure on the fertility and longevity of the parasitoid Anaphes flavipes

Entomologia Exp Applicata

Skuhrovec

et al. 2019

Self Cite

“…We are aware that although the presented two-generation approach may provide a more accurate view of the population dynamics of gregarious parasitoids, determining fertility from parasitoid body size requires extensive measurements. As an alternative, we propose obtaining knowledge of factors such as host availability 11,12 and characteristics 13 or the presence of a predator of the host 11 with which the parasitoid female “consciously” changes the clutch size and, thus, the body sizes of the offspring and their future fertility values. With knowledge of these factors in a specific environment, we can expect a decrease or increase in parasitoid clutch size and determine their population dynamics using a two-generation approach.…”

Section: Main Textmentioning

confidence: 99%

A novel two-generation approach for understanding the population dynamics of gregarious parasitoids

Raška

et al. 2021

Preprint

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The population density of animals is generally measured as the number of individuals. Here, by using gregarious parasitoids as models, we show that this traditional approach omits one important parameter: the clutch size - body size - fertility correlation. Using this correlation, female gregarious parasitoids deliberately adjust the number of offspring laid in a host, determining not only the number of offspring but also the body sizes and reproductive potentials of those offspring. We propose a new two-generation approach for determining the population density of gregarious parasitoids. Using this new approach, which includes the clutch size - body size - fertility correlation, we show that the same fertility in the F1 generation can cause distinctly different fertility values in the F2 generation, and that, even with the same number of hosts, lower fertility in the F1 generation can cause higher fertility in the F2 generation. Our two-generation approach provides a new perspective for determining the individual fitness levels of gregarious parasitoids with new options for the modelling of parasitoid population dynamics.

“…The females can lay one to seven offspring at any sex ratio into a single host, resulting in 35 possible combinations in a clutch (Anderson & Paschke 1968). By changing clutch size, the females are able to respond to different external conditions (Samková et al 2019b) and we predict that they can also change the offspring sex ratio. Importantly, A. flavipes is a potential agent for biological control against major crop pests of the genera Lema and Oulema (Coleoptera: Chrysomelidae) from Europe and North America (Linnaeus, 1758) (Dysart et al 1973, Samková et al 2017, Skuhrovec et al 2018).…”

Section: Introductionmentioning

confidence: 95%

“…In this study, we measured the effect of clutch size on the sex ratio of offspring developing in one host to assess the above-mentioned assumption that larger clutch sizes should contain more male offspring (Yu et al 2003). Secondly, we examined the offspring sex ratio in individual females under the pressure of external factors that affect clutch size (different host population density and the presence of the host’s predator; Samková et al 2019b). Again, the tested assumption was whether the proportion of male offspring will increase with larger clutch size.…”

Section: Introductionmentioning

confidence: 99%

“…Again, the tested assumption was whether the proportion of male offspring will increase with larger clutch size. However, since we previously showed that these external factors help determine the body size and fertility of the F1 generation (Samková et al 2019b), we took this one step further and examined the effect of fertility on the sex ratio, discussing the results of our experiments from two generation approach, i.e. the perspective of both F1 and F2 generations.…”

Section: Introductionmentioning

confidence: 99%

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Female manipulation of offspring sex ratio in the gregarious parasitoidAnaphes flavipesfrom a new two-generation approach

Raška

et al. 2021

Preprint

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Both theoretical and empirical work suggests that offspring sex ratio has important consequences on fitness. Within insects, gregarious parasitoids with haplodiploid sex determination represent an ideal model for studying the decision-making process behind the assignment of offspring sex. To gain insight into the offspring sex ratio of gregarious parasitoids, we performed experiments on Anaphes flavipes, interpreting our results through a two-generation approach. We confirm the existence of a relationship between offspring sex ratio and clutch size: the proportion of males increases with larger clutch size. Based on this finding, we assumed that the proportion of males among one females offspring would also increase with external factors such as a low population density of the host or the presence of the hosts predator, which may pressure the mothers to lay a higher-sized clutch. Contrary to our initial expectations, we show that if it is the pressure of external factors that leads to an increase in clutch size, these larger clutches tend to be more female-biased and the overall offspring sex ratio of a particular female does not change. While in our previous work, we showed that higher clutch sizes reduce body sizes of the offspring and their future fertility, here we conclude that the differences in fertility affect the offspring sex ratio. Taken together, we highlight our two-generation approach which reveals that while the above external factors do not affect the sex ratio of A. flavipes in the F1 generation, they do have an effect in the F2 generation.