Tag Archives: parasitoid

Melittobia staking out a mason bee house

I recently set up a mason bee house, and almost instantly attracted a parasitoid, a female Melittobia. She was so tiny that I first thought it was a thrips. But its behavior was odd and definitely not thripsy. The insect would linger near the holes that were being used by mason bees (Chelostoma philadelphi and Osmia sp.), approach, then scurry away, then repeat. On one occasion it peered down an unoccupied hole and paused for several seconds before walking away. It was covered in wood shavings, too, so I inferred that she’d been inside the holes on at least one occasion. All this activity screamed, “parasitoid”, of course, so I had to get some pictures: 

Female Melittobia sp. at a mason bee house.Female Melittobia sp. at a mason bee house.Female Melittobia sp. at a mason bee house. I’m not sure which species she is (there are 14 according to González et al. 2004), but I gather that all members of the genus can parasitize mason bees. Females spend up to 48 hours lurking around a hole (“assessing” per González article) and then puncture a developing larvae with her ovipositor, drink some of the hemolymph, and deposit eggs. There’s a pause in between the hemolymph-feeding and the egg-laying, presumably to allow some of the nutrients to be allocated to eggs. Females are not at all picky about host larvae. Recorded hosts for M. acasta include honeybees, bumblebees, leafcutting bees, and various wasps, flies, beetles, and butterflies (González et al. 2004).

Things get exciting when the wasps eclose, with the early-emerging male killing the slackers that are still developing. There are two types of females: brachytperous (reduced wings) and macroptyrous (regular wing size). I’m assuming the one(s) I viewed are the regular kind.

I’ll post more photographs if I can get them, but whatever is going on inside the holes is of course hidden. But I’m going to make a few glass-sided mason bee houses in the next few weeks so hopefully I can get some larval pics one of these years. This spotting is a reminder to use paper tube inserts whenever possible so that larvae can be examined at the end of the season for parasites. I’m rather interested in parasites but I’d like to encourage a healthy mason bee population when possible.

Much thanks to Ross Hill for identification, and of course to people behind BugGuide for facilitating such IDs. These observations are also logged into iNaturalist.

Tricrania sanguinipennis, a bee parasitoid

Found this striking, highly punctate beetle in my yard a few days ago and finally figured out what it is: Tricrania sanguinipennis, a blister beetle (Meloidae). Apparently a parasitoid of Colletes spp., ground-nesting bees that are often situated in dense aggregations. I have hundreds of digger bees in my front yard each year, so I’m guessing that some or all are Colletes, but I’m trying to confirm (casual guess is C. inaequalis, the unequal cellophane bee).

Colin Purrington Photography: Insects &emdash; Tricrania sanguinipennis

Per Parker and Böving 1924, female T. sanguinipennis deposit clumps of eggs near these aggregations and when larvae hatch they seek out adult bees and clamp onto body hairs with specialized mandibles. If the bee happens to be a female, larvae release their grip when she arrives at the brood cell, sometimes up to 2 1/2 feet underground. If the beetle larva has attached to a male bee it will move onto a female while the bees are mating. Once in the nesting chamber the larva will seek out the bee egg, eat it, then set up camp inside the cell (see fig 21, below) that holds the honey and pollen, which it will eat until maturity.

Below is Plate 3 from the Parker and Böving article. If you expand the image you can see that the bee has multiple larvae attached. I think I might need to capture a few of the bees this Spring to see whether I can find some of these hitchhikers. Am also trying to find the egg clumps, which can have thousands of eggs. That’s a lot of eggs for a beetle but the success rate of the larvae must be extremely small so they’ve presumably evolved large brood size to ensure that at least some find their way into a nest.

Tricrania sanguinipennis

Illustrations of Tricrania sanguinipennis larvae from Parker and Böving 1924.

Very cool beetle and just had to share the find. If you’d like to see more photographs, there are currently 27 sightings Tricrania sanguinipennis on iNaturalist. I highly recommend the Parker and Böving article for the biology details but mainly for how they figured out the details; it’s hard to figure these things out when the species spends its life underground. For more information on related beetles this page by Dr E. F. Legner (UC Riverside) is excellent.

Anthrax alert in Pennsylvania

Just in case you’re a fan of obscure diptera, I wanted to share some images of an insect I’d never seen before: Anthrax georgicus.

Colin Purrington Photography: Insects &emdash; Anthrax georgicus

I initially identified it as Ogcodocera analis, which looks exactly alike to the untrained eye (like mine) but isn’t found in Pennsylvania. Anthrax georgicus parasitizes tiger beetles, apparently. The females lay eggs near the entrances to tiger beetle burrows and then the larvae attach to the beetle larvae and suck hemolymph. If you live near a place with dense population of tiger beetles, keep your eyes peeled for this fly. Or read about them here, in a fantastic post by Matt Pelikan. I gather they lay eggs by dive bombing.

The next photograph shows what it did in response to my flash.

Colin Purrington Photography: Insects &emdash; Anthrax georgicus with wings spread

I searched around to see if all flies do this, but couldn’t find anything about light-induced wing spreading. I did find an article by Andrei Sourakov on the startle response of a long-legged fly, again caused by a flash — they exhibit a tumbling escape behavior (see paper for pics). In a separate paper, Sourakov discusses the startle response of skippers (Hesperiidae) — again, I highly recommend taking a look at the figures so you can see the insects during their escape tumbles. In hindsight, I should have played around with flash sync speed to see if I could measure how quickly it could spread its wings. The shutter speed I was using was 1/200 second.

Just in case I’m completely wrong about the ID (which I based on this page) and you’re an expert with a moment to spare, I put a better view of a wing at the bottom. The posterior margin of the alula looks convex. I don’t have a better view of the antennae, unfortunately, which I know would be helpful for Bombyllidae. As a side note, insects that are jet black but have shiny white parts are a complete pain to photograph.

Anthrax georgicus wing close-up