by Erica Sarro, Ph.D. Candidate
Twitter: @erica_sarro

Each spring, as the snow begins to melt and warm weather approaches, young bumble bee queens emerge, one by one, from underground burrows. They’ve waited out the winter in these burrows. These queens likely haven’t eaten since fall, so they quickly begin searching for their next meal. In Yosemite, like in much of the western United States, spring queens feed primarily on the pollen and nectar from manzanita flowers. Manzanita is one of the earliest and most abundant flowering plants in the region. It is at large stands of manzanita in early May of 2019 that my field assistants, Claire and Charlie, and I searched for queens of the yellow-faced bumble bee, Bombus vosnesenskii.

​Once the queens were collected, we brought them back to the lab at the University of California Natural Reserve System Yosemite Field Station. We set them up in nest boxes so that they could start their own colonies. In the wild, these queens would find a suitable nest site (likely an abandoned rodent burrow or other underground hollow) and lay their first set of eggs. Instead, our queens laid these eggs in cotton-lined boxes in the lab. We fed the queens sugar syrup (as a substitute for nectar) and pollen to sustain them while they incubated their eggs and those eggs hatched into larvae.

Once the queens had larvae that were a few days old (and thus had an established nest that they would be motivated to return to in order to feed their brood), the real experiment began. We tagged each queen with a radio frequency identification (RFID) tag (more on this later) and put their nests out into the field. We placed the nests within mesh tents over sections of meadow, somewhat like a natural, open-air greenhouse. These tents enabled us to control which flowers the queens had access to. Our basic question was: Do queens adjust their food collection (foraging) behavior in response to different resource environments? Essentially, if we put some queens in tents with sparse flowers, and some queens in tents with lots of dense flowers, will the queens in these different environments forage differently? We predicted that queens in areas with sparse flowers would forage more often and for longer periods of time than queens with dense flowers. This is because queens with sparse flowers would have to work harder to access the same amount of nutrients as those with dense flowers. This is an important question to know the answer to, because the more time queens spend collecting food, the less time they have to incubate their brood. In bumble bees, the more frequently larvae are incubated, the faster they develop. So, if a queen has less time to incubate her brood because she has to work harder to collect food, her offspring will take longer to develop. That means her colony will grow more slowly. Bumble bee colonies only live one season. If development time is slowed down and the colony gets a late start, this may limit the ultimate growth and success of the colony.

We connected each nest box entrance to an RFID reader box. The RFID readers recorded the time and duration of every foraging trip each queen took. When the queen passed through the RFID reader box, it read the unique RFID tag affixed to her thorax and recorded a precise timestamp that we could analyze later.

We also monitored the tents for several hours each day. Any time we saw that a queen was out and foraging, we video recorded the queen’s foraging bout. This would enable us to analyze the amount of time each queen spent visiting flowers of specific species, flying between flowers, resting outside the nest, or carrying out other behaviors. This information would help us better understand queen foraging. We repeated this at multiple field sites with different queens.

We were successful in collecting and rearing the queens, finding flower-filled meadows and setting up the tents, and working out the kinks with a new RFID system to record queen movements. Unfortunately, as with most fieldwork, we did run into some unforeseen obstacles. Particularly, we learned that some queens don’t take kindly to being in tents. They often flew into the mesh sides or perched on the ceiling or walls of the tent for hours at a time. Some even abandoned their nests altogether and spent the nights outside on the ground! Unfortunately, we weren’t able to answer the questions we set out to answer this season. But we learned an important lesson here: wild animals are wild, and we can’t always predict how they’re going to respond to the things we throw at them. That’s science. Things don’t always go as planned. You can do everything right, but if your study organism doesn’t like it, there’s often little you can do. But with the RFID system up and running, and the queen collection and rearing down, I am excited to take these skills and apply them to new and related projects to better understand the foraging biology of early nesting bumble bee queens.
 
Queens only forage early in the season. Once they successfully rear their first set of offspring to adults, those daughters (they’re all female at this point in the colony!) will take over the foraging and brood care responsibilities so that the queen can focus on laying more eggs and growing the colony. In the early nesting stage, the queen is the sole forager, and the actions she takes can make or break the success of her colony. Partly because the queens only forage for a short time, we know very little about what they forage on, when they forage, how frequently and for how long they forage, and how they make these foraging-related decisions. With future research, I plan to further investigate queen foraging behavior to better understand how queens make these decisions, and how these actions impact colony development and success. See you next field season, queens!

You may wonder, “How can a wasp be amazing and remarkable?”  Let me count the ways . . .
 
1. O. mirus is less than 1 mm long, yet it has 4 wings, 6 legs, eyes, a brain, digestive and reproductive systems, etc. It can perform complex behaviors, like determining how many eggs to lay based on the size of the host species’ egg.
 
2. Most of the individuals are females, and they do not need males in order to reproduce.  They do not mate even if a male shows up and initiates a courtship ritual.  A male approaches a female head-on, waving his antennae into the female’s antennae.  She waves back for a second, and then turns around and walks away .  I feel bad for the males, doomed to eternal unrequited love!  The males seem to be an artefact from an earlier time in the species’ evolutionary history when mating was needed for reproduction.
 
3. Oddly, a type of bacteria called “Wolbachia” is responsible for making the wasps mostly female.  I can kill the Wolbachia by feeding the wasp antibiotic-laced honey, or by keeping the wasps at 97°F (= 36°C).  Without the Wolbachia, the second generation is 100% males.  That ends that experiment, because the males cannot reproduce!
 
4. The adult female wasps usually lay only one egg into a host bagrada bug egg, with a tail sticking out from the wasp egg through the outside shell of the host egg, as an air tube for the baby wasp.  The parent wasp probably injects some venom, too, because I have only seen one case in about 5,000 parasitized host eggs where the host survived and a baby bug emerged.  (In entomology, “bug” refers to a specific group of insects.)   Normally even if no wasp emerges, no bug emerges, either.  The wasp egg hatches inside the host egg and the baby wasp spends its whole childhood in there, consuming the host egg, as if in a small, external womb.  After a few weeks, it pupates into an adult and chews its way out of the host egg shell.  The wasp is especially cute at this point, because the antennae pop out first and start waving in the air, and then the head slowly appears, and then the rest of the body, over about an hour’s time.  
 
5. When I kept parasitized eggs at 57° or 61°F for a couple of months, no wasps emerged.  However, when I transferred the same eggs to 79°F, wasps emerged 10 days later, instead of the usual 14 days at 79°F.  Thus it looks like the wasps develop into larvae even at the cooler temperatures, but then they stop and wait until the temperature is more to their liking. 
 
6. Even though bagrada bug appears to be its main host, my wasp was able to reproduce successfully on the eggs of 9 other species of bugs and one species of moth, the corn earworm.  The only species I tried on which O. mirus did not succeed was the carob moth, probably because the moth eggs were too small.
 
7. Last but not least, O. mirus is easy to rear and to work with.  Our colony has gone through about 44 generations in Quarantine at UCR since we first received them from Pakistan in January, 2016, and, knock on wood, we have not had any diseases or problems.   
 
For these and many other reasons, I am proud to introduce to you my “baby,” Ooencyrtus mirus !

by Madison Sankovitz, Ph.D. Student
Twitter: @MSankovitz

Ants are some of the most widespread and numerous insects on Earth, making up an estimated 15-20% of all terrestrial animal biomass. Along with their dominance of so many different habitats, ants contribute significantly to the modification and maintenance of ecosystems. Ants are considered ‘ecosystem engineers’, which means that they change the biological, chemical, and physical properties of the habitats in which they live. Many ants nest in soil, which they modify through foraging and nutrient cycling, as well as nest excavation. We know that ants modify the soil in and around their nests, but not the extent to which this occurs in different ecosystems.

​I am a Ph.D. student and I’m interested in how physical factors that vary between ecosystems, like temperature and precipitation, play a role in how ants interact with the soil of those ecosystems. To investigate this, I’m conducting a study with data from two California mountain ranges: San Jacinto and Sierra Nevada.

Most of my day is spent thinking about invisible things. Well, not quite invisible, just reeeeally small. The tiny things I spend every waking hour (and most sleeping ones) obsessing over are the following: bacteria, DNA, and impossibly small wasps. And yes, I think of them all at the same time. I study symbiosis. Here is what The Oxford English Dictionary has to say about symbiosis:

noun (plural symbioses ˌsɪmbɪˈəʊsiːzˌsɪmbʌɪˈəʊsiːz)
[mass noun] Biology
1. Interaction between two different organisms living in close physical association, typically to the advantage of both.

Symbioses are common. We are in a symbiotic relationship with all the bacteria in our guts, for example. My favorite symbiotic relationship is between a bacterium known as Wolbachia, and a very small wasp known as Trichogramma.

The image that often comes to mind upon hearing the word "wasp" is that of a large, black and yellow insect that stings and lives in a nest with others of its kind. Trichogramma don't fall into this category: they are less than half of a millimeter in length, they prefer the solitary life, and they wont sting you. In fact, most wasps are more like Trichogramma, we just don't notice them. And while they may not sting you, the females will sting something. That something might be a tree, another insect, or even another wasp. When a small Trichogramma stings its preferred sting-ee (moth and butterfly eggs) it is in fact laying an egg. Once Trichogramma inserts an egg, the wasp will develop inside of the moth egg, eating what would have hatched into a caterpillar. A week or two later, instead of a wee caterpillar, an adult wasp hatches out of the egg shell. This is known as parasitism; Trichogramma is a parasitoid wasp. Other species of parasitoid wasps will lay their eggs in or on caterpillars, spiders, grubs, maggots, eggs of other insects, you name it. There are estimated to be more than half a million species of parasitoid wasps, each with their own particular preferences of where to lay eggs. There is a whole world of these tiny creatures out there that most are not aware of.

In the laboratory, we can watch all this happen.