This depends on the viewpoint:

a) Parasitoids are a special type of predators whose larval stages live inside or outside a living host; the host dies after pupation/hatching of the parasitoid larvae.

b) From a food web perspective, every organism that consumes prey/food at multiple trophic levels can be considered an omnivore.

Thank you. Would you know any article that discuss omnivory based on host-parasitoid networks? I read that compartimentalization may be an important stability factor in host-parasitoid networks. However, I would not expect them to be specially compartimentalized if there is a high level of omnivory...but I might be mixing two different concepts.

It depends about which parasitoid group are we talking about. For example, aphid primary parasitoids are not omnivorous (feed only on aphids), but their secondary parasitoids often are (may feed on primary as well as on other secondary parasitoids).

Dear Valérie,

Good question. If we define omnivory as feeding on several trophic levels, and we assume trophic levels are (more or less) discrete entities, I would say that primary parasitoids (whether they are host generalist or specialists) are not onmivorous. Secondary (the same applies to tertiary and so on) parasitoids are always omnivorous if they are facultative (i.e., either they feed on uninfected or on infected by a parasitoid herbivore hosts), but obligate hyperparasitoids (those that only feed on already infected hosts) hyperparasitoids are not omnivorous.

Best,

Jose

Thank you for these interesting answers. What I get is that it depends in part to the level of specialization. I won't be as "categorical" as Jose for primary parasitoids (unless I am wrong with my understanding of primary parasitism). For example a parasitoid that attacks both bee and wasp species as a primary parasitoid will feed on two different trophic levels. It is therefore an omnivorous.

In fact the question came in my mind as I read this blog article that shows how omnivory increases as we go up the food chain:

http://assemblingnetwork.wordpress.com/2013/04/18/it-is-a-tangled-bank-up-there/#comment-185

I wondered if we could find such a relationships for host-parasitoid networks or if it would be even the contrary.

Best,

Valérie

I find the answer of Ramzi especially interesting. I had not think about that way, That's true that adult parasitoids consume nectar, whereas the larvae is rather "predatorous". Thus we have an additional consideration to do: threat each stage independently or not? Of course they are not truly independent, but the importance of nectar resources for parasitoids is seldom considered in host-parasitoid networks I think.

Dear Valérie - I tend to agree with Andreas: functionally, I don't consider them omnivores (even though they s.s. may feed on different trophic levels, i.e., on herbivores and predators (parasitoids). Although one can consider, e.g., a soil spider that feeds on detritivores and other spiders an omnivore, from my point of view the most important (functional!) aspect of omnivory is whether they feed on both producers and consumers. I would expect the more direct effects of intra-guild predation (in the above example) to overwhelm the more indirect effects of this "hidden omnivory"...?

However, this is certainly an interesting question that I would have to think about in some more detail...

Cheers,

martin:-)

Dear Valérie,

I am not sure why you wouldn't consider parasitoids that require floral resources as omnivorous? Predators also consume plant material of some kind are considered omnivorous. The real issue is if and how we can detect and measure these interactions. Currently in most parasitoid food webs we ignore this component of their life-cycle because it is difficult to quantify, not because it isn't important.

Links you might find useful:

http://www.bugwood.org/arthropod/day4/wratten.pdf

http://www.nature.com/scitable/knowledge/library/omnivorous-insects-evolution-and-ecology-in-natural-23864519

Cheers,

Sarina

Hi Sarina - if the parasitoids, beside feeding on their host and other parasitoids, also feed on vegetal tissue, it will -of course- be considered omnivorous (obviously I missed part of the basal information?). If, however, it is adult versus larval stages that feed on vegetal versus animal tissue, the answer will not be that simple (albeit interesting!)...

Many inverts shift food sources upon ontogenetic development - should we consider all of them omnivorous?

Hi Martin, it wouldn't be a bad idea. Then we could ask some really interesting questions about when and why they shift food sources, and what this means for growth and development? I am probably getting a bit off topic now though.....Cheers, Sarina.

Hi Sarina - off-topic questions are sometimes the most interesting ones;-)

It might, indeed, be a good idea, but this would then question in general the categorization of feeding types into these groups (which, in turn, might not be a bad idea after all...) - even if we don't follow this suggestion, asking "when" (upon maturation/pupation?) and "why" they shift would be most promising... (but this is really off-topic now - sorry, Valérie!)

Dear all,

Thank you very much! No problem with off-topics, it is really interesting and highlight the complexity of considering the place of parasitoids in the ecological communities. What I find really exciting is that through its different stages and host range, a single parasitoid can couple many different trophic levels. Instead of having energy flowing from one trophic level to the other (classical food chain), we have energy from several trophic levels flowing to a single parasitoid species. However, this is not restricted to parasitoids. For example, predatory wasps also need nectar as an adult and hunt prey for their larvae. Anyway, it is a real challenge to assess every possible interactions and processes that might influence the diversity and structure of an ecological community!

Best,

Valerie

Hi Valerie!

I would just like to add to the discussion here, although it is also off topic. Your question highlights the ambiguity of the definition of a parasitoid and I believe defining parasitoids as omnivores would help classify their type of exploitation in ecological communities. As you know, parasitoids are classified as a type of parasitism, however as it eventually kills its host, it could technically be understood as predation. If a parasitoid switched to vegetal tissue, would that species still be considered a predator? Perhaps not, but I think the term omnivorous would still be very applicable.