The Prevalence of Egg Parasitoids of Two Cobweb Spiders in a Tropical Urban Gradient

Parasitoidism strongly influences the structure of the spiders’ populations, and it can be affected by environmental factors such as those caused by anthropogenic actions. We studied the prevalence of parasitoids in egg sacs and the proportion of eggs parasitized in each egg sac of two synanthropic spider species, one native to the American continent (Parasteatoda tepidariorum) and another recently introduced to the Americas (Latrodectus geometricus). We conducted the study at two scales, along an urban gradient (from highly urbanized to rural sites) and in the vegetation surrounding each sampling site (microscale). We expected to find a larger prevalence of parasitoids in the most urbanized sites and around sampling sites with more vegetation. However, we saw more parasitized egg sacs at the intermediate urbanized site for both species, and the vegetation surrounding the sampling sites did not affect the number of parasitized egg sacs. Therefore, conditions in the site with intermediate urban development favored parasitoids. We also found more parasitized egg sacs in P. tepidariorum than in L. geometricus, which is likely a consequence of native parasites not being adapted to a new host. The proportion of eggs parasitized was similar for both species in all sites, which may be related to the behavior (e.g., searching behavior) and number of spider eggs a female parasitoid can parasitize.