Why can the nymphs of Cacopsylla chinensis respire in honeydew?

Cacopsylla chinensis, a terrestrial insect, was studied for its nymph's respiratory mechanism in honeydew through series of immersion experiments.The survival of C. chinensis nymphs in water under different immersion conditions was studied.

The respiratory system structure of C. chinensis nymphs was analyzed via the lactic acid immersion method. And the scanning electron microscope was employed to observe the spiracles' ultrastructure of C. chinensis nymphs.

The results showed that under natural conditions, the immersion rates of 1^st to 5^th instar C. chinensis nymphs in honeydew were all exceeded 76.00%, with the 2^nd instar nymphs exhibiting the highest immersion rate (99.00 ± 1.00)%.The median lethal time of C. chinensis nymphs under immersion conditions was 12.47 h, and the nymph mortality rate increased gradually with prolonged immersion time. C. chinensis nymphs had five pairs of spiracles, including two pairs on the thorax and three pairs on the abdomen. The nymphs respired underwater or in honeydew by the air bubble film formed by the densely distributed ultrafine hydrophobic setae (approximately 90 μm in length) located under the wing buds and around the abdominal spiracles. However, when non-ionic surfactants were added to water, the air bubble film was eliminated, and the underwater respiration of C. chinensis nymphs was significantly impaired. After only 10 minutes, the nymph mortality rate reached (95.00 ± 1.83)%. This study indicates that the air bubble film formed by hydrophobic setae of C. chinensis nymphs around their spiracles were used to respire in water or honeydew.

Based on the above findings, this study provides a scientific reference for the sustainable and ecological control of C. chinensis.