This week yet another unimaginable calamity if Paris Accord is not fulfilled. That’s right the coordinated reports in the media raise the alarm: The Insects Are Coming For Us (unless we mend our ways!)
Global warming will help insects, hurt crops NBC News
Climate change may boost pests, stress food supplies Axios
Climate Change Will Lead To More Crop-Destroying Insects IFLScience
Global Warming Means More Insects Threatening Food Crops — A Lot More, Study Warns InsideClimate News
Global warming will likely help bugs devour more crops CBC.ca
Global warming could spur more and hungrier crop-eating bugs ABC News
Global warming could spur more crop-eating bugs CTV.ca
Global warming will make insects hungrier, eating up key crops: study AFP
Crop losses due to insects could nearly double in Europe’s bread basket due to climate EurekAlert!
Climate change projected to boost insect activity and crop loss, researchers say EurekAlert!
Rise in insect pests under climate change to hit crop yields, study says Carbon Brief
Swarms of insects will destroy crops across Europe and America by 2050 due to global warming Daily Mail
Global warming: More insects, eating more crops Phys.org
Climate change to accelerate crop losses from insects Cornell Alliance for Science
Climate Change Means Insects Are Coming for Our Food The Atlantic
Well, at least we know who is keen to reprint press releases from Alarmist Central. I am not an entomologist, not are the journalists who are piling on this story. So let’s hear from some insect experts.
First, a tutorial on Temperature, Effects on Development and Growth (Insects)
Adult insects generally are of smaller body size when larvae are reared at higher temperatures. For example, females of Bicyclus butterflies reared at 20°C were larger than those reared at 27°C. Moreover, females laid larger eggs when they were reared or acclimatized for 10 days at the lower temperature compared to the higher temperature.
LDT: actual lower developmental threshold; T0: predicted lower developmental threshold; UDT: upper developmental threshold; TO: thermal optimum (maximum) for developmental rate. Total optimum for population growth is usually at moderate temperatures, not at such high extremes.
Development time (dt) is the time required to complete specified stage or instar and can be described as dt = SET/(T-T0). SET is the sum of effective temperatures or “thermal constant,” expressed as the number of degree days. T0 is the lower developmental threshold (LDT, or base temperature Tb), the hypothetical temperature at which developmental time would be infinite or developmental rate would be zero. The product of developmental time and the amount to which ambient temperature is above the threshold was found to be constant (= SET), that is, development will take a fixed number of degree days essentially independent of the temperature at which the animal is reared. The thermal parameters are determined in defined conditions (set of constant temperatures, suitable nutrition).
The LDT and SET values are population-specific characteristics. The LDT values are similar for all developmental stages of a given population, even when they develop in diverse seasons and experience disparate temperature fluctuations. The stability of LDT is manifested as developmental rate isometry, that is, the percentage of time spent in a particular stage at any constant physiological temperature is a stable fraction of the entire developmental time.
Tropical species have higher values of LDT than temperate ones. SET decreases as LDT increases. Insects that have spread to temperature zones from the tropical regions often maintain a high LDT and can reproduce and develop only in the hot season, spending most of the year in a state of dormancy.
A general response of insects to temperatures just below their LDT or above their UDT is the cessation of development and reproduction while the insects remain active and feed. The larvae may slowly grow and the adults accumulate reserves. These processes are terminated at more extreme temperatures.
During cooling, motility gradually decreases. At certain temperature, the neural and muscular activities are impaired and the insect lapses into cold stupor (chill coma). The stupor point is as high as 12°C in tropical insects including stored product pests, and in honey bees, around 5°C in many temperate species, near 0°C in most overwintering insects, and even below the freezing point in species living in very cold areas.
Gradual warming above UDT, which is for many species around 35°C but is never sharply delimited, increases the metabolic rate, loss of water, and motility. Around 40°C, the water loss increases sharply: the spiracles are wide open and the melting of cuticular lipids permits evaporation through the body surface. Exhaustion of water and nutrients leads to rapid decrease of motility and a drop of transpiration. At a certain temperature, heat stupor occurs. Survival at temperatures above the threshold is a function of temperature and length of exposure. Warming to the absolute upper lethal temperature, which is usually around 50-55°C, causes fast, irreversible tissue damage and death.
The data for terrestrial ectotherms discussed previously point to species from mid-latitudes in particular being closest to their thermal maxima. Moreover, although data are still quite scanty, species may have only a limited capacity to deal with changes in upper thermal limits. Under an expected 2–4 °C warming scenario (IPCC 2007), mid-latitude populations near limits are likely to face the threat of extinction because they cannot adapt to new environmental conditions.
There is almost no information on how thermal limits are influenced by combinations of stressors. Changes in the conditions that organisms experience during thermal stress could lead to quite unpredictable upper thermal limits (Terblanche et al. 2011; Overgaard, Kristensen & Sørensen 2012). Moreover, thermal stress can influence susceptibility to other selective agents; tropical Bicyclus anynana butterflies lose immune function as measured by phenoloxidase (PO) activity and haemocyte numbers when exposed to warm conditions, and the effects are particularly marked when adults have a limited food supply.
These scares always sound plausible, but on closer inspection are simplistic and unrealistic. The above shows that each type of insect has a range of temperatures they can tolerate and allow them to develop. They are stressed and populations decrease when colder than the lower limit and also when hotter than the upper limit. Every species will adapt to changing conditions as they always have. Those at their upper limit will decline, not increase, and their place will be taken by others. Of course, if it gets colder, the opposite occurs. Don’t let them scare you that insects are taking over.