February 2023 Bulletin

Xylocopa wing morph, in-person bee course, overwintering bees, spring bees

Shutterbee observations used in published paper

Earlier this month, Nina published a paper examining wing color in the eastern carpenter bee, Xylocopa virginica in the Journal of the Kansas Entomological Society. A few years back, a master’s student in Dr. Gerardo Camilo’s lab (Paige Muñiz) found that some Xylocopa she caught had a lighter portion on their wings. This lack of color had never been documented before, but it was found in ~10% of the Xylocopa caught in St. Louis. Paige and Gerardo asked people who manage insect collections all across the county if they had seen the morph before, and nobody had.

Most large insect collections are from sampling in rural areas. We suspected that the loss of pigment (melanin) was an adaptation to warmer temperatures associated with cities. The light sections of the wing absorb little heat and thus the individual is able to be active during the hotter parts of the day.

Fortunately for us, iNaturalist observations are frequently from cities. Therefore, we decided to look through observations on iNaturalist to see where else across the species range we could find evidence of wing de-melanization in Xylocopa. Nina Fogel and former undergraduate Madeliene Thompson looked through 35,696 observation on iNaturalist and found 533 bees with pigment missing on their wing.

Blue dots show the 533 bees found on iNaturalist

We found evidence of Xylocopa with the wing morph in 30 out of 35 of the states and provinces that make up the species’ range. Three of the five states without evidence of wing de-melanization are the northernmost edge of the range—Vermont, New Hampshire, and Maine. Another northern state, Wisconsin, had a single observation. The metro areas of St. Louis, MO, Houston, TX, and Dallas, TX represented 54.6% of the morphs found! This means that this morph is more common than insect collections indicated.

We were unable to determine the mechanism or pigment loss nor whether there are any advantages or disadvantages to the de-melanization. There’s always more research to be done!

Many of the St. Louis photos were taken during Shutterbee surveys. You can see if your photos were used by searching for your username at this link.

A PDF of the whole paper is here.

Sign up for in-person bee ID course

On Saturday, April 1st we will host a semi-structured in-person bee identification course. 

The course will be a few hours long and will be an opportunity to look at specimens under a microscope. You will get to practice bee ID using the Shutterbee guide, ask questions, and look at multiples species of the same genus close up. 

Please fill out this form if you are interested.

We may not have room for everyone, so we will prioritize people who have attended bee id course and/or worked to identify their own or other people’s observations on iNaturalist. 

Where the wild bees are (in winter)

Variety is the spice of life, and not just for humans. Bees overwinter in all sorts of materials AND life history stage. Some bees overwinter in the ground and some in twigs. Some bees overwinter as pupa, others as adults. Recently, Kathy Bildner found a surprise when she rolled over a piece of wood in her yard: female pure green sweat bees (likely Augochlora pura)!

Female pure green sweat bees overwintering in decomposing wood.

Bees overwinter in all sorts of materials AND life history stage. Some bees overwinter in the ground, some in twigs, some (like these beauties) in wood. Some bees overwinter as pupa, others as adults. Like bumble bee queens, these female bees fully develop the prior year, mate with males, and then “hibernate” as adults overwinter. Unlike bumble bees (which we think mostly nest in the soil or leaf piles), pure green sweat bees overwinter in rotting wood! When overwintering, adult insects go into a state known as “torpor” (rule of thumb for the difference between torpor and hibernation: is it voluntary or just physiological? For insects, it’s a physiological response to changes in the environment. They don’t make a decision to start the process. Bears, on the other, do, so they hibernate). When in torpor, insects are in a “sleep-like” state: lower physiological activity, metabolism, and body temperature. This helps them maintain low energetic costs while they await warmer temperatures.

Spring bees are almost here!

This warm winter might mean an early year for some bees. As it warms, some overwintering bees begin to use more energy, even in torpor. Once their energy reserves are gone, they need to find flowers to replenish. However, if temperatures then cool off again, they are in a tough spot – no reserves left and no flowers on which to flower. Many species use temperature cues, such as “growing degree days” (how many days are warm enough to support plant growth), as an indication for when to emerge from their winter rest. They will remain in torpor despite some temperature fluctuations, but once there have been enough warm days, they emerge, hopefully at the same time as their host flowers. This type of cue is very common for spring organisms. As we all know, weather can change quickly in the middle of the continent, so things could change. But having several, consecutive days of warm temps may just push the bees out of torpor. Time will tell!

Two species of bumble bee whose emergence from torpor is triggered by growing degree days: Bombus bimaculatus (PC: Lisa Brunette) and Peponapis pruinosa (PC: Kerry Zimmerman)

Despite the fact that spring is on its way and our bee friends may be emerging soon, we aren’t starting our Shutterbee surveys until May. We encourage you to take opportunistic photos of the bees in your gardens as they emerge and upload them to iNaturalist. However, our official “Shutterbee season” doesn’t start until later this spring. We will send out a registration form in our next bulletin, for all new and returning participants to fill out. We are asking that all folks officially register for two reasons. First, we want to collect some demographic data that we previously only requested of those individuals who participated in the human behavior research. Second, we are planning some new experiments this summer and want to plan our sampling locations accordingly. We look forward to working with all of you again this year!

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