Wasp Wednesday Week 10: Antistrophus Gall Wasps

This week is all about the gall wasp genus Antistrophus, my most recent research obsession. Read on to find out what makes this group especially exciting, and why their conservation is critical to endangered North American ecosystems!

 

This group is part of the family Cynipidae, a group of over 750 species that are known to occur worldwide. Cynipidae contains a number of subgroups called tribes that are categorized by host plant – Cynipini (oak gall wasps) is currently the most diverse based on the number of known species, but this group also received the greatest attention in research. The other 11 tribes are all equally interesting and worthy of study, especially Aulacideini, which contains many types of herb gall wasp and includes the genus Antistrophus.

Antistrophus currently consists of 10 species that all form galls on plants of the family Asteraceae, particularly Silphium, Chrysothamnus, Lygodesmia, and Microseris. The most noteworthy of these is the first one, Silphium: this genus includes a number of important plants that are specialists in North American prairies. Prairie ecosystems in North America are among the most threatened habitats – as much as 99% of their former geographic range has been cleared, primarily for use as agricultural land, meaning the conservation of the remaining habitat is a critical goal for conservation biologists.

When Antistrophus galls are found in prairies, they are often incredibly abundant, although they are often entirely unseen. Most species induce imperceptible galls within the stems of their host plants that can’t be detected from the outside – the only way to tell if the galls are even there is to cut a stem open and examine the internal tissue for signs of galling. In fact, only one known species will produce always-visible galls: Antistrophus silphii produces large, club-like galls at the tips of Silphium stems, which can grow to one or two inches across!

Because of their abundance and galling lifestyle, Antistrophus wasps play an especially important role in prairie systems as so-called “ecosystem engineers”, as they act as the foundation of an absolute ton of ecological interactions between many different organisms. The foremost of these would be parasitic wasps, especially those in the superfamily Chalcidoidea – these insects entirely rely on Antistrophus wasps to complete their own lifestyles, and need to lay their eggs in galls in order to reproduce. Many other animals also eat or otherwise interact with these galls, meaning that Antistrophus wasps drive a large amount of activity in prairie ecosystems. Evolutionarily, the presence of these wasps has greatly influenced the development of prairies, but we’re still uncovering how they’ve fostered the diversity and functionality of these systems. As a result, these wasps are crucial considerations within conservation programs concerning prairie systems where they occur!

We’re still learning to understand the importance of these wasps in their native ecosystems, but the emerging picture appears to be that these insects will remain an important study topic for decades to come! Silphium, the same host plant that makes Antistrophus an important prairie insect, is currently being domesticated for use in biofuels, which brings even more relevance to these gall wasps. We’re also uncovering possible undescribed species within the genus! Overall, examining this crucial group of gall wasps will undoubtedly yield many valuable insights into prairie conservation, biotechnology, and systematics!

View This Taxon On: BugGuide | iNaturalist

The photos of Antistrophus silphii and Antistrophus jeanae have been graciously provided by Frost Museum research associate and Hines Lab postdoctoral scholar Antoine Guiguet – you can see more of his work, including more photos of gall wasps, on his website!