Oriental butterfly uses glitter to choose leaves

Females of Mole Grapholite retain the ability to distinguish brightness and light intensity in environments with irregular lighting, suggests a study by Chinese scientists. The result indicates consistent use of visual cues in choosing oviposition sites, even under conditions similar to those found in orchards at dusk.

The research evaluated the preference of females between light green and dark green stimuli. The study also compared posture in areas with higher, medium, and lower light intensity. The tests were conducted under uniform light, simulated dappled light, and complex dappled light. The scientists used three illuminance levels: one hundred lux, one lux, and zero point zero one lux. These values ​​correspond to twilight, late twilight, and moonlight.

Under all conditions, females laid more eggs on the light green stimulus. Preference occurred at all three illuminance levels. Damp light did not reduce brightness discrimination. The same pattern occurred for light intensity. Females concentrated egg laying in areas of higher intensity, with a frequency greater than sixty-six percent.

Pest in rose bushes

Mole Grapholite occurs as a pest of peach, pear, apple, and other rosaceous plants. Females typically lay eggs on young leaves located at the top of host plants during dusk. Previous studies had already indicated a preference for greater brightness and higher light intensity in low-light conditions. The new work evaluated whether heterogeneous canopy light could alter this behavior.

The researchers set up the experiments in cardboard boxes measuring 20 centimeters by 20 centimeters by 30 centimeters. Light green and dark green rectangles, measuring 5 centimeters by 10 centimeters, were arranged on the inner walls. The stimuli simulated young and old peach tree leaves. A white LED lamp illuminated the system from above, more than 50 centimeters from the box.

To simulate speckled light, the scientists used filters with light green, dark green, and transparent areas. In the complex speckled light treatment, a second layer with vertical stripes was superimposed on the initial pattern. Each experiment had ten repetitions, with one hundred moths per condition.

The tests began at 5 p.m., three hours before the start of the scotophase. Ten mated females, three days old, were placed in each box. They had fifteen hours during the night to lay eggs. The following morning, the researchers removed the females and counted the eggs deposited in the light green and dark green rectangles.

Statistical analysis

Statistical analysis indicated a significant preference for light green in uniform light, speckled light, and complex speckled light. The response occurred at 100 lux, 1 lux, and 0.01 lux. The study also recorded a significant preference for zones of higher light intensity in all combinations tested.

According to scientists, the stability of this response may help the species locate suitable oviposition sites in orchards, where branches and leaves create an uneven distribution of light during much of the growing season. The researchers also highlight potential applications in management. Understanding brightness preference can aid in the development of visual strategies, such as traps or repellent surfaces with higher light contrast.

More information at doi.org/10.3390/insects1706055