pondering question about pepsis wasp

[JohnDapiaoen]

I was watching videos of pepsis attacking different kinds of spiders on youtube and it occurred to me that all the spider victims looked to be adult females or close to being adult. will a wasp ignore a spider unless it's at a certain size or greater or even a male? From what I understand the point of parasitizing the arachnids in the first place is not to feed oneself but to feed the carnivorous offspring while the adults feed on nectar. So I'm thinking maybe attacking a smaller spider result in a starving wasp larva. I'm just curious about this and maybe someone here has some info they can share or thoughts?

-JohnD.

 

[Smokehound714]

True pepsis species only go for larger tarantulas. As they're generally huge wasps, they need their host to be large enough to sustain the larva.

However hemipepsis is a smaller species that will take smaller specimens, including wolf spiders.


The tribe pepsini is quite variable in size, with hemipepsis generally growing no larger than 20mm.

Perhaps the slow growth rate of aphonopelma triggered speciation within pepsini.. Sometimes, there will be no adult tarantulas available to the wasps..

 

[Le Wasp]

Interesting observation! A lot of parasitic wasps have an interesting ability of choosing the gender of their offspring, and will usually put their female offspring into larger hosts. The larger the host, the larger their offspring will be; and a small son isn't as bad as a small daughter. Especially if their daughters have to grow up to be able to fight with tarantulas! A dwarfed daughter wouldn't be able to produce many/any eggs and probably wouldn't be very good at overpowering a tarantula. --a small male could still produce plenty of sperm and deliver it decently well enough.

I would guess that tarantula hawks would put their male eggs into smaller tarantulas, but I'm not sure if they'd avoid male tarantulas altogether. Also, I'm not sure if Pepsis is a type of wasp that's able to control their offspring's sex. It's possible they can't choose, and thus should always try to get the biggest tarantulas, just in case they lay a female egg.

 

[Smokehound714]

As a solitary group, I doubt they have the advanced gender control that social species possess..

in fact, I believe males tend to make up the bulk of a pepsis' offspring, considering how common they can be.

I'll often see dozens of males playing king of the hill on ceanothus or eriogonum..

Then again, perhaps they do control the gender of each egg.. A bunch of females would probably extirpate their own species by stinging too many tarantulas.

 

[Le Wasp]

Actually, gender control is seen in plenty of non-social wasps. Producing their females only in the larger hosts is beneficial to most parasitoids.
I wonder if those groups of males congregating on flowers is some kind of mating lek. I don't think tarantula hawks are very well studied, but it sounds like there's plenty of interesting stuff to work with.