Rose Gall Parasitoids

I am in the process of rearing out some rose gall wasp species to send to Stephanie Eskew at Colorado State University, she is working on the phylogeny and studying the gall communities of the genus Diplolepis. About a week or so ago, I took the D. ignota galls that I've collected this winter out of the fridge. Over the last day or two, adult wasps have started to emerge. Today was the first chance I had to start looking at them and preserving them in alcohol to send to Stephanie to further study them. So far, it looks like only parasitoids have emerged. In a few days I would guess that the gall inducer and hopefully some inquilines will begin to emerge. 

Diplolepis ignota gall on prairie rose (Rosa arkansana)

Gall communities are extremely complex, especially those of the gall wasps (Cynipoidea) which often have more complex gall structures and often occupy their galls for 1-2 years. In contrast, many of the gall midges (Cecidomyiidae) leave their gall after mere days or weeks, up to a year. For most gall wasps, the adult will lay an egg on the proper part of the host species. Once that larva hatches it will produce plant hormones and other chemicals that induce the growth of the gall. That larva will continue to feed on the gall tissue, eventually pupate, often go through winter diapause, and emerge as an adult. Providing ample time for other species to take advantage of the habitat provided by the gall.

A 2 year study out of Canada found 55-65% mortality of Diploloepis nodulosa galls caused by the inquiline Periclistus pirata. Another 17% mortality rate was caused by 6 different species of parasitoids. And add another 13% from other undescribed inquilines. This is typical for gall-associated communities, usually there are multiple species of parasites/inquilines found within the gall, not to mention all the other interactions that occur outside of the gall. In fact, the California oak gall wasp (Andricus quercuscalifornicus) has so many relationships with other organisms that it is considered a keystone species as well as an ecosystem engineer.

Typical gall wasp community, image from Plant Galls of the Western United States (Russo)

Some of these interactions are well studied, most are not. In many cases little is known about the gall inducers, let alone their associated communities, which brings us to Stephanie's work, and me rearing wasps to send to her. 

As I said, today I was only looking at wasps that emerged from D. ignota galls. I have a few other Diplolepis galls, and some modified by Periclistus that I am also rearing out. I'm sure plenty of interesting things will emerge from those as well, I'll be posting those updates soon. From what I could tell, there are quite a few species of parasitoids, all chalcid wasps (superfamily Chalcidoidea), an extremely diverse and understudied group with 20,000 some described and an estimated 500,000 species in total. That diversity is absolutely mind-blowing; for context the current total for described species of mollusks, arachnids, crustaceans, fishes, reptiles, birds, amphibians, mammals, and corals combined only totals 384,547. Just like the chalcid wasps that number is an underestimate, but it gives some perspective. From the wasps I reared, there seems to be a few species in the family Torymidae, a few Eurytomidae, and at least one species of Eupelmidae. Chalcid wasps are notoriously hard to identify to species (even sometimes genus), at least for amateurs like me. Some of these species are likely undescribed, hopefully Stephanie will be able to get a more precise identification. I assume that there will potentially be a few more species that will emerge in the coming week from these galls. 

The complex relationships and astounding biodiversity associated with these galls is absolutely amazing. There is so much variation in the color, size, abdomen/ovipositor shape, and overall appearance of these wasps. Many of the chalcid wasps are very beautiful with metallic colors. They are often pretty reflective; I've taken some pictures, but I'll have to get much better at my macrophotography to do these specimens justice, especially with staging and lighting. But, these photos have been good enough for a general identification so far. Below are just a handful of the pictures I have taken.

Chalcidoidea sp.

Eurytoma sp.

Eurytoma sp.


Torymus sp. 






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