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By Laura Weingartner

A root maggot spends most of its life underground. An entomologist spends his time studying these insects. For a few short weeks in the summer, the adult fly pushes its way to the surface and celebrates life by finding a mate and laying its eggs at the base of the plants that will feed its young. The entomologist devises a plan to determine precisely when this happens. 

The entomologist, in this case, is Dennis Fielding, who recently retired from the University of �山���� Agricultural and Forestry Experiment Station. 

One of his favorite things about his job was getting to know insect species like the root maggot. He studied not just their phenology — the timing of important life events — but also their biology and behavior. By unearthing the intricacies of the lives of the root maggot and other pests, Fielding's work can provide information on how to manage these insects to help farmers grow successful crops. 

Knowing the timing and duration of an insect laying its eggs is necessary for pest management. In the case of root maggots, adult flies start laying eggs soon after emerging in the late spring. When those eggs hatch, the larvae immediately migrate downward in search of the roots they tunnel into for food, ruining crops for farmers and gardeners alike. 

After a few weeks of feasting, molting and growing, they pupate in the nearby soil, where they develop a protective shell in which they start their transformation into adults. As temperatures drop, the pupae enter diapause, suspending further development until spring. 

Before his retirement, Fielding designed experiments to collect these root maggot pupae in the fall and bury them under the traps set up at the experiment farms in Fairbanks and Palmer. The following spring, warm soil is their alarm. The pupae wake up, grow into their final form, surface as flies and make their way to the top of the trap. 

By monitoring the traps, Fielding could calculate the number of pupae that survive into adulthood and the timing of their emergence. He has found that some populations in some years have a bimodal emergence pattern: Some emerge early in the season, then there is a lull in activity. Another group from the same population emerges later. 

“There’s like an extended diapause,” he says, describing the behavior. This split between early and late risers could be an assurance that host plants are available when the flies are ready to lay their eggs. 

Proactive farmers can use this information to determine control methods. For example, insecticides are more effective when applied as eggs are laid. Additionally, protective coverings that exclude pests and their eggs but allow air and water to pass through need to be in place before flies are active. Finally, growers can adjust planting dates to minimize root maggot impact. Rapidly growing crops such as radishes, for example, might be planted early enough to harvest before root maggots are active or as they taper off.

While there are about 300 species of root maggots globally, Fielding focuses on the three that are pests in Alaska: the turnip root maggot (Delia floralis), the onion root maggot (D. antiqua) and the seed corn root maggot (D. platura). Their names indicate their food preferences and host plants. These root maggots can cause significant damage to host plants, lowering the amount of marketable crops or even killing the whole plant. 

Because root maggots can be such a nuisance, Fielding also designed experiments to determine how long crops are exposed, if he can lure maggots toward pest-preferred plants grown alongside main crops and if, with climate change, root maggots could complete a second generation in one season. 

 

Fortunately, “it would have to be quite a bit warmer to get a successful second generation,” Fielding says. 

While root maggots were a major focus during his time with AFES, Fielding spent a long time investigating grasshoppers as an entomologist with the U.S. Department of Agriculture’s Subarctic Agricultural Research Unit (ARS). When he starts to talk about grasshoppers, his eyes light up. Considering he made an exciting discovery explaining the biennial highs and lows of grasshopper populations, this may not be surprising. 

Grasshoppers in Alaska require two years to complete their life cycle. Cold climates mean a short growing season for developing insects, and many insects at high latitudes go through two winters in their egg stage, making developmental progress during the warmer months. They hatch early in their second summer, rapidly maturing, reproducing, then dying. 

Since at least 1990, these grasshoppers have been observed to have population booms and busts in Delta Junction on alternating years, with populations 10 to 100 times greater in even-numbered years than in odd-numbered years. Fielding describes his proposed mechanism for why this happens: parasitic flies. 

Sarcophagid flies, tachinid flies and other flies that parasitize grasshoppers in Alaska have one-year life cycles. They lay their eggs or live larvae on their grasshopper hosts, and the larvae burrow in and start eating. After about two weeks of gluttony, a full-grown maggot emerges, usually killing the grasshopper. It then pupates, usually in the soil nearby, and the adults emerge the following summer.

 

On even years in Delta Junction, where Fielding studied this phenomenon, grasshoppers are abundant, giving flies plenty of hosts and high reproductive success. In alternate years, the fly population has grown, and the flies kill so many grasshoppers that there aren’t enough hosts for the parasites. Thus, both the odd-year grasshopper population and the fly population drop. The progeny of the abundant even-year grasshopper population only has to contend with a small number of flies the following season. Their out-of-sync life cycles perpetuate the boom and bust cycle of the grasshoppers, giving farmers a break from these pests eating their crops every other year.  

Reflecting on his career, Fielding admits he found himself a scientist by accident. Following his interest in agriculture, he kept finding exciting pest management projects and ended up with a doctorate from the University of Illinois. There he studied the squash bug, a pest that sucks sap from the fruits, stems, leaves and vines of squash plants. After a postdoc in Idaho working primarily on grasshoppers, he reluctantly moved to Alaska for a job with the U.S. Department of Agriculture. While not enthusiastic about the move at the time, he still finds himself here after almost 30 years. 

The move to Alaska influenced some of his work. 

“The season is compressed here, everything happens really fast,” Fielding says, summing up the main difference between studying insects in Alaska and the Lower 48. 

Fielding compared Idaho populations to those in Alaska, revealing some interesting findings about how grasshoppers have adapted to shorter growing seasons. They grow faster, weigh less, and convert digested food to biomass at higher rates, using nutrients more efficiently. In short, they’re in a rush and they get to work. 

Fielding retired in the fall of 2024. While he is still publishing some of his findings, unlike the insects he studies, he’s no longer in a rush to get to work.

 

Laura Weingartner is the science communicator for the Institute of Agriculture, Natural Resources and Extension.