Factors shaping life history traits of two proovigenic parasitoids

Abstract

What shapes the relative investment in reproduction versus survival of organisms is among the key questions in life history. Proovigenic insects mature all their eggs prior to emergence and are short lived, providing a unique opportunity to quantify their lifetime investments in the different functions. We investigated the initial eggloads and longevity of 2 proovigenic parasitoid wasps: Anagrus erythroneurae and Anagrus daanei, (Hymenoptera: Mymaridae) that develop within leafhopper eggs in both agricultural vineyards and natural riparian habitats in Northern California. We collected Vitis spp. leaves containing developing parasitoids from 3 natural sites (Knight Landing, American River and Putah Creek) and 3 agricultural vineyards (Solano Farm, Davis Campus and Village Homes). We recorded eggloads at parasitoid emergence and female parasitoid longevity with or without honey-feeding. Theory predicts that parasitoids from vineyards (where hosts are abundant) would have higher initial eggloads and lower longevity compared with parasitoids from riparian habitats (where hosts are scarce). Although host density and parasitoid eggloads were, indeed, higher in vineyards than in riparian habitats, parasitoid longevity did not follow the predicted pattern. Longevity without feeding differed among field sites, but it was not affected by habitat type (natural vs agricultural), whereas longevity with feeding was not significantly affected by any of the examined factors. Moreover, longevity was positively, rather than negatively, correlated with eggloads at the individual level, even after correcting for parasitoid body size. The combined results suggest a more complex allocation mechanism than initially predicted, and the possibility of variation in host quality that is independent of size.

Trait-based approaches to predicting biological control success: challenges and prospects

“…Moreover, the allocation of resources between fecundity and other traits may be highly dependent on environmental conditions (see also 'Variable environmental contexts' below). For example, in a simulation model of parasitoid life history evolution [28], the optimal allocation between egg load, egg size, and adult longevity, depended on host and food availability in the environment, in agreement with empirical data comparing parasitoid traits in natural versus agricultural environments [29,30]. Thus, traits that promote success under certain environmental conditions may not guarantee high performance in others.…”

The combined effect of host and food availability on optimized parasitoid life‐history traits based on a three‐dimensional trade‐off surface

“…Similarly, in L. boulardi , females from humid environments invested more in early reproduction, but died sooner than females from dry environments (Moiroux et al, 2010). In contrast, no clear evidence for such an opposite response was found in Anagrus parasitoids, as females originating from host‐rich environments, despite a higher investment in egg number at emergence, did not seem to consistently reduce investment in survival (Segoli, Sun, Nava, & Rosenheim, 2018), but instead produced smaller eggs (Segoli & Rosenheim, 2013b).…”

Temporal variability in host availability alters the outcome of competition between two parasitoid species

“…Likewise, proovigenic parasitoids constitute a much smaller proportion of parasitoids of Drosophila flies in natural ecosystems than synovigenic parasitoids (Fleury et al 2009). This could be because the high energy costs of maintaining mature eggs mean that proovigenic life histories come at the expense of shortened lifespans and reduced host efficiency when the temporal availability of host resources is highly unpredictable (Segoli et al 2018; Rosenheim et al 2008). The abundance of Drosophila flies in natural ecosystems is closely dependent on resources such as rotten fruits or mushroom that themselves have high temporal variability, further influencing the temporal availability of hosts for parasitoids.…”

“…Proovigenic parasitoids have eggs that are mature at or shortly after adult emergence and lay their eggs over a relatively short period, while synovigenic parasitoids have eggs that mature gradually during their longer lifespan (Jervis et al, 2001;Segoli & Rosenheim 2013a). Reproductive success of parasitoids may be limited by the availability of mature eggs for synovigenic parasitoids, and by the availability of suitable hosts for proovigenic parasitoids (Rosenheim 1996;Segoli et al, 2018). We predict that when small numbers of hosts are continuously exposed to parasitoids over an extended period, long-lived synovigenic parasitoids will be favoured, but when hosts occur at high density for short periods, proovigenic parasitoids with plentiful mature eggs will be better able to (which was not certified by peer review) is the author/funder.…”