Maggot dreams

by Cheyenne Tait – When you’re joining a lab that focuses on a species complex of non-model univoltine insects, which are largely interesting because of the geographic patterns they exhibit, one thing should be obvious: the need for wild-caught insects to be collected from the field each year. For some reason, when I started studying Rhagoletis, this did not seem like such a big deal. In fact, collecting fallen fruit, infested with larvae, sounded like a good break from the primarily indoor grind of a genetics/neurophysiology project. But, four years later, I look forward to field seasons, occurring from late July through October, with a mixture of both dread and excitement.

I am a student at the University of Notre Dame, Indiana, doing part of my PhD at the NICE lab and splitting my time between the locations. A large part of the reason I am at Notre Dame this fall in particular, and not returning to the NICE lab until the spring, is because field season is such a lot of work and my Notre Dame lab needs all hands on deck!

A typical field day begins before dawn, with a mad scramble to pack everything we might need (where someone will inevitably leave their field shoes sitting in the parking lot). This is followed by the chaos of packing the 18 passenger field vehicles our department supplies, agonizing over whether we’re bringing enough buckets, whether we want the net, and whether we need the hockey stick. After a coin flip to see who drives the monster van, we’re off on our adventure!

It begins with a ride lasting several hours and several hundred miles (further if we get lost in spite of our GPS), to locations ranging from northern Michigan to southern Illinois and all points in between. Since I study the apple and hawthorn races of Rhagoletis pomonella, this is as far as I go. Other members of my lab study members of the Rhagoletis genus that infest walnuts (southwestern USA) or those infesting snowberries (heading west out along the northern USA to Washington state), or those in deerberries and sparkleberries (Kentucky, Tennessee, and further south). They go on field collection trips lasting upwards of two weeks and racking up thousands of miles!

There’s plenty of excitement on trips that last one (very long) day. From the expected: mosquitoes, high humidity, thunderstorms, and poison ivy, to the unexpected: horse flies larger than ping pong balls, a bog that’s taken over the field site, the abrupt disappearance of blueberry bushes the lab has collected from for a decade, or the closure of our favorite Mexican restaurant… Field collection season is definitely never boring! It also allows us to interact with the public, explaining our project to people that walk by and ask (if our field site happens to be at a parking lot, for instance), or to landowners who graciously allow us to use their land.

Field collection days only end when we’ve picked enough fruit to fill all containers (including lunch bags if necessary), or if, even when we hook the branches with the hockey stick and shake the tree as hard as possible, it won’t give up any more fruit. Upon arrival back at Notre Dame, we unload our fruit into our greenhouse, into wire mesh cages over planting trays, so that the emerging larvae, expecting to come out of the apple and hit the soil, then burrow down and pupate for the winter, instead are confined to the trays for us to collect daily.

So field collections do not end in the field. Each day someone has to check all the trays, count the larvae into petri dishes, and store them in the fridge at 4 C for a simulated overwintering period. This is truly the tedious part of field collection season: we handle thousands of larvae per day. Larvae that are vitally important to so many projects, so are handled with lots of focus and care. We half-seriously wonder about where we should put “maggot husbandry” on our CVs, and after several months of counting and focusing so intensely on them, most members of the lab can still see maggots even after we close our eyes for the night.

There are also other species of insects within the apples, that we see both in the field and in the greenhouse. From wasps to butterflies, moths to beetles, to larval stages of all of the above, we know more about what can live in an apple than we ever truly wanted to know. We also joke about the insects we throw into the trash, that some other graduate student somewhere probably studies this one and throws our Rhagoletis in the trash! The diversity of insects underscores the complexity of our system, the interspecies dynamics affecting our flies that must vary between species and between geographic sites. For instance, in walnuts there are competing fly larvae that at first we could not differentiate from the Rhagoletis larvae. It was only after they started to coil up and spring themselves across the room, similar to the larvae in so-called jumping beans, that we realized that this was definitely not the species that we wanted!

The diversity of host fruit varieties is also striking. For instance, we collect a lot of apples from across a north-south gradient. Generally southern apples ripen before northern apples, but even that does not always hold true. Rhagoletis flies also generally prefer sweet, red, soft apples, but this year we established a new site that’s very productive, where the flies are in hard, late-ripening green apples. And at another site, red apples and yellow apples occur side by side, and, while both are heavily infested, it seems like the yellow apples are just a little bit more popular. It all just again reminds you that there are more things going on in nature than you can ever really account for.

Ultimately, although I spend long 18 hour days in the field collecting fruit, and many more hours in the sweltering greenhouse taking care of the Rhagoletis larvae, I feel this work lets me appreciate my study species all the more. And those days when we’re out in the field at just the right time, in just the right weather, to see the flies on the apples, mating and ovipositing like they’ve evolved to do, that’s just the icing on the cake.

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