Studying environmental changes in bees

Measuring critical thermal maximum of bees in temperature ramping experiment.

Climate chambers have long been used for their versatile application purposes. Whether in the market for a humidity chamber, constant climate chamber, plant growth chamber, and environmental test chamber and more, customers are likely to find their best fit. Read more about climate chambers, their types, uses, applications here for other thermal product solutions.

Sensors such as humidity sensor and more, in combination with innovative, industry leading climate control technology as found in the Peltier element, can make for a solid climate chamber capable of several tasks.

One such unique application of the Memmert HPP750eco, powered by Advanced Peltier Technology, is taking part in the thermal tolerance experiment which measures critical thermal maximum, CT_max, for bees to understand their differential sensitivity to urbanization-driven changes in body temperature and water content, as experimented on by Justin D. Burdine and Kevin E. McCluney. This research was conducted at Bowling Green State University and published by its Biological Sciences Faculty.

You can download the report here.

Bee population at risk due to environmental changes?

A fall in population or extinction can be explained by climate change and adverse effects of how land is being used today.

One could ask why it is important for scientists and researchers to know how species react to such things. Chiefly among the reasons are conservation of living organisms and maintenance of our ecosystems.

Although in such a vast world many species are studied with numerous devices, the HPP750eco plays a key role in determining how bee conservation can be kept healthily in an ecosystem.

This article explains the background and the key part where the constant climate chamber HpPP750eco comes into play.

Factors affecting bee response to environmental conditions

With species population decline or, even worse, extinction, as a worst possible case, as the study explains, services provided such as pollination are at danger of being disturbed or degraded with such taxa decline.

Physiological tolerances of species as well as desiccation tolerances are important to predict how these living forms react to global change and how it impacts survival.

What is thermal tolerance?

This measures the response of the species to changes in temperature. Critical thermal maximum and critical thermal minimum come into effect at this point. These two, alongside thermal safety margins are metrics used by experts to determine how organisms are responding to climate change and environmental conditions from a physiological perspective.

Define critical thermal maximum and critical thermal minimum

Per Burdine and McCluney, this is, “an organism’s upper sub-lethal temperature and CT_min the lower sub-lethal temperature, and these are the temperatures at which an organism loses muscular control and suffers an ecological death.” The different between CT_max and CT_minis called thermal range.

What is thermal safety margin?

This refers to the differences between CTmax and either optimal body temperature, field body temperature, or air temperature, and offers a metric for understanding vulnerabilities to warming. As a general of thumb, based on findings, natural temperature gradients affect the thermal tolerance. Burdine and McCluney further add, “There is also evidence that insect thermal tolerance varies across smaller climatic gradients. Body size (surface-volume ratios) may also influence thermal tolerance, because smaller animals dissipate heat better but may be more prone to desiccation.”

Taking desiccation tolerance into account

Desiccation tolerance refers to the “ability to survive drying to about 10% remaining bee c, which is roughly equivalent to 50% relative air humidity (RH) at 20°C (=water potential of - 100 MPa)” ( Alpert, 2006; Oliver et al., 2010). It is suggested that a fruit fly desiccation tolerance falls as precipitation increased in Australia, per Hadley in Water Relations of Terrestrial Arthropods. Additional evidence also points to desiccation tolerance varies geographically for Mediterranean fruit flies. Such studies and more can conclude that desiccation tolerance could predict how environmental conditions such land use and climate change affect living beings. The high surface area to volume ratio and higher water loss to metabolic rate ratios also make a stronger case for smaller organisms like bees with regards to desiccation.

Critical water content

An important factor contributing to desiccation is the critical water content. This refers to the water content in the body of the organism at death. The CWC is calculated gravimetrically as the difference between wet and dry mass, divided by wet mass.

Urbanization and its adverse effects on bee population

Land use and global climate change affect both thermal and desiccation tolerances of bees. It is known that changes in temperatures, moisture availability affects body water content of arthropods. Bee temperature tolerance can be looked into in this regard as critical thermal maximum can be used to predict how population changes across urbanization gradient. Other factors are urban heat islands in high temperatures. In fact, insect water balance changes can also negative impact growth, reproductivity and survival rates.

The experiment

The experiment conducted looks at how a gradient of urbanization (impervious surface, e.g. areas of pavement), in a medium-sized city, alters both the critical thermal maximum, CT_max, and critical water content, CWC, of bee species.

Bees used

From the diverse bee communities, three species were studied for this experiment:

Silky striped sweat bee (Agapostemon sericeus)
Western honeybee (Apis mellifera)
Common eastern bumblebee (Bombus impatiens)

A good reason to use three types of bees was explained that they differ in size, foraging preference, sociality, and nest specificity, increasing the likelihood of detecting differential responses among species.

Figure 1: Western honeybee (Apis mellifera). Image courtesy of John Quine.

Thermal tolerance experiment of bees using HPP750eco

A Memmert constant climate chamber HPP750eco was used in the thermal tolerance experiment. Here, critical thermal maximum was measured for each species of bees. The constant climate chamber helped with the temperature ramping which started at 25 °C that was raised at a rate of 0.5 °C min−1 as per standard methods. Temperature and humidity sensors in the device, powered by its Peltier element, helped with the readings. With regards to humidity, it was kept constant at 20% due to the suitable humidity sensors working within. The bees were placed inside the climate chamber individually in specimen cups where its mesh covering allowed for air temperatures in the cup to be raised alongside increases with the temperature ramping of the HPPeco.

Righting responses were carried out with a puff of air. With its loss, the experiment indicates an endpoint when muscle functions begin to fail, and is commonly used to estimate CT_max. Bees that could move upright in a 15 second window past receiving the puff of air are considered to have lost their righting response.

Critical thermal maximum is considered here as the temperature where the righting response was lost. At this point, the bees were taken out of the climate chamber. The HPP750eco’s temperature ramping continued until all the 90 bees used in the experiment had reached their CT_maxwhich took about two hours.

The bees were weighed, kept in air-tight vials afterwards. Bees were not fed nor given water in the temperature ramping section.

Thermal tolerance experiment of bees using HPP750eco — Figure 2: Constant climate chamber HPP750eco.

Findings

Thermal and desiccation tolerances vary for each bee species and in their safety margins as well
Urbanization and climate change led desiccation might affect honeybees
Sweat bees are sensitive to changes in temperatures
More data is needed for bumblebees’ reaction to temperature changes and water balance differences

About Memmert products

Memmert GmbH + Co.KG builds on this and offers its own range of industry leading climate chambers capable of the applications above and more. Peltier cooling and heating come in handy in several applications done in Memmert products. The Peltier element is capable of translating the theory into practice for Advanced Peltier Technology powered devices like the Constant climate chamber HPPeco and Peltier-cooled incubator IPPeco, Memmerts offers the following climate chambers:

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