Featured Image Caption: Predatory mite mothers produce drought-resistant eggs when the mothers experience drought conditions. (Source: Egor Kamelev via Pexels)
Reference: Le Hesran, S., Groot, T., Knapp, M., Bukovinszky, T., & Nugroho, J. E. (2020). Maternal effect determines drought resistance of eggs in the predatory mite Phytoseiulus persimilis. Oecologia, 192, 29-41. https://doi.org/10.1007/s00442-019-04556-0
Celebrating “Mite”-y Mothers
With Mother’s Day right around the corner, people from all over the world will celebrate – perhaps many from a distance this year – all of the love and support mothers have provided throughout the years. As infants, humans are completely dependent on parents to keep them safe because their small size and inability to move or effectively communicate make them vulnerable. However, human mothers aren’t the only mothers that offer care to ensure the survival of their children.
Mite eggs are similarly defenseless due to their small size and immobility. Conversely, mite eggs cannot eat or drink to compensate for water loss. On top of that, mite eggs can face environmental challenges that threaten their survival, such as fluctuating temperatures and humidity. How is it possible for mite eggs to survive stressful environments? The eggs have mothers that prepare them for the worst.
Humidity and Eggs
Phytoseiulus persimilis is a predatory mite that is often used to control populations of two-spotted spider mites, a pest that is a detriment to many woody plants and crops. Therefore, the persistence of the predatory mite is vital for agriculture, and eggs need to be able to survive variable environments. Fluctuations in humidity are especially stressful for mite eggs since water vapor in the air can influence whether or not the eggs dry out. If humidity is high, the eggs can soak in a lot of water from the air. Low humidity, similar to a drought, may cause the mite eggs to dry up and die. How could mite mothers help their eggs to survive these variable conditions? A team of researchers in the Netherlands was determined to find the answer.
Sophie Le Hesran and her colleagues put adult predatory mite females in different treatments of humidity: constant high humidity, constant low humidity, and switching from low to high humidity. After the mothers laid eggs, the eggs were placed in low humidity which simulated drought conditions. The researchers recorded the number of eggs the mothers laid, how many eggs successfully hatched, and the survival of the mothers.
When mite mothers were exposed to constant low humidity, more drought-resistant eggs hatched than eggs from mothers exposed to constant high humidity. When mothers were moved from low humidity to high humidity, the number of eggs hatching dropped because eggs from mothers exposed to high humidity were not equipped to survive drought conditions. Female mites in low humidity lived shorter lives and produced fewer eggs. Because low humidity conditions are not ideal for mites, it is assumed that producing more drought-resistant eggs requires excess energy.
Mom to the Rescue
When the humidity is low and eggs are at risk of drying out, predatory mite mothers produce drought-resistant eggs to promote the survival of their offspring in a drought. Since drought-resistant eggs require excess energy to produce, the mothers in low humidity produce less eggs and live shorter lives. In doing so, mite mothers foster the persistence of their offspring.
The flexibility in the type of egg produced allows this species to persist even when environmental stressors are variable. The predatory mite’s existence is essential for the control of the two-spotted spider mite pest. This pest infests over 200 species of plants and has had huge economic impacts on vegetable crops and greenhouses. Phytoseiulus persimilus feeds on all life stages of the two-spotted spider mite and is considered to be one of the most important tools to control this pest. Thanks to mite mothers, variable humidity will not stop predatory mites from pest control. Mite mothers, like human mothers, equip their offspring to survive difficult times. So, this Mother’s Day, let’s appreciate and celebrate all that mothers do, both human and mite alike.