An intergenerational approach to parasitoid fitness determined using clutch size.

Parasitoids, as important natural enemies, occur in high numbers and help maintain balance in natural ecosystems. Their fitness is traditionally studied as fertility based on the number of offspring in the F1 generation. Here, using gregarious parasitoids as models, we show that this traditional approach omits one important parameter: the clutch size-body size-fertility correlation among offspring. As a result of this correlation, when females adjust the number of offspring laid in a host, they determine not only the number of offspring produced but also the body size and reproductive potential of those offspring. Although parasitoid fertility has been determined several times from clutch size, here we use Anaphes flavipes to demonstrate the use of this relationship in an upgraded intergenerational approach to parasitoid fitness. We show that with a range of hosts simultaneously utilized by female parasitoids, identical fertility in the F1 generation can lead to distinctly different fertility values in the F2 generation. Even with the same number of hosts, lower fertility in the F1 generation can generate higher fertility in the F2 generation. Our approach provides an intergenerational perspective for determining individual fitness of gregarious parasitoids and new possibilities for the modelling of parasitoid population density.

Effect of host switching simulation on the fitness of the gregarious parasitoid Anaphes flavipes from a novel two-generation approach.

Herbivorous insects can escape the strong pressure of parasitoids by switching to feeding on new host plants. Parasitoids can adapt to this change but at the cost of changing their preferences and performance. For gregarious parasitoids, fitness changes are not always observable in the F1 generation but only in the F2 generation. Here, with the model species and gregarious parasitoid Anaphes flavipes, we examined fitness changes in the F1 generation under pressure from the simulation of host switching, and by a new two-generation approach, we determined the impact of these changes on fitness in the F2 generation. We showed that the parasitoid preference for host plants depends on hatched or oviposited learning in relation to the possibility of parasitoid decisions between different host plants. Interestingly, we showed that after simulation of parasitoids following host switching, in the new environment of a fictitious host plant, parasitoids reduced the fictitious host. At the same time, parasitoids also reduced fertility because in fictitious hosts, they are not able to complete larval development. However, from a two-generation approach, the distribution of parasitoid offspring into both native and fictitious hosts caused lower parasitoid clutch size in native hosts and higher individual offspring fertility in the F2 generation.

Host Specificity of the Parasitic Wasp Anaphes flavipes (Hymenoptera: Mymaridae) and a New Defence in Its Hosts (Coleoptera: Chrysomelidae: Oulema spp.).

The parasitic wasp Anaphes flavipes (Förster, 1841) (Hymenoptera: Mymaridae) is an important egg parasitoid of cereal leaf beetles. Some species of cereal leaf beetle co-occur in the same localities, but the host specificity of the wasp to these crop pests has not yet been examined in detail. A lack of knowledge of host specificity can have a negative effect on the use of this wasps in biological control programs addressed to specific pest species or genus. In this study, laboratory experiments were conducted to assess the host specificity of A. flavipes for three species of cereal leaf beetles (Oulema duftschmidi Redtenbacher, 1874, Oulema gallaeciana Heyden, 1879 and Oulema melanopus Linnaeus, 1758) in central Europe. For the first time, a new host defence against egg parasitoids occurring in O. gallaeciana from localities in the Czech Republic, a strong dark sticky layer on the egg surface, was found and described. The host specificity of A. flavipes was studied in the locality with the presence of this defence on O. gallaeciana eggs (the dark sticky layer) (Czech Republic) and in a control locality (Germany), where no such host defence was observed. Contrary to the idea that a host defence mechanism can change the host specificity of parasitoids, the wasps from these two localities did not display any differences in that. Respectively, even though it has been observed that eggs with sticky dark layer can prevent parasitization, the overall rate of parasitization of the three species of cereal beetles has not been affected. However, in our view, new host defence can influence the effects of biological control, as eggs of all Oulema spp. in the locality are protected against parasitization from the wasps stuck on the sticky layer of the host eggs of O. gallaeciana.

Illustrated key to European genera, subgenera and species groups of Mymaridae (Hymenoptera), with new records for the Czech Republic.

Illustrated keys to females and males of the European genera and subgenera of Mymaridae (Chalcidoidea) are presented, including twenty-four genera plus two subgenera in both of Erythmelus Enock and Polynema Haliday. The key to females also includes three subgenera recognized in Anagrus Haliday, two subgenera in Anaphes Haliday, and two species groups in Anagrus s.s.; males of these either cannot be distinguished or are difficult to key. The species of Mymaridae recorded from the Czech Republic are listed and distribution records are provided based on material in three collections. Seven genera (Anagrus, Caraphractus Walker, Dicopus Enock, Macrocamptoptera Girault, Omyomymar Schauff, Pseudocleruchus Donev Huber, Stethynium Enock) and 12 species are newly recorded for the country.

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

The number of parasitoids developed per host is one of the major factors that influences future adult body size and reproductive success. Here, we examined four external factors (host species, heritability, host population density, and presence of predators) that can affect the number of the gregarious parasitoid Anaphes flavipes (Förster, 1841) (Hymenoptera: Mymaridae) wasps developing in one host. The effect of host population density on the number of parasitoid offspring developed per host was confirmed, and for the first time, we also showed that the number of offspring per host is influenced by the presence of predators. Low host density and presence of predators increases the number of wasps developed in one host egg. However, a higher number of A. flavipes in one host reduces A. flavipes body size and hence its future individual fertility and fitness. Our results highlighted the importance of some external factors that distinctly affect the number of wasp offspring. Therefore, in this context, we suggest that in comparison to solitary parasitoids, the gregarious parasitoid A. flavipes can better respond to various external factors and can more flexibly change its population density.