Protective effects of the egg stalk of Paratrioza sinica (Hemiptera: Psyllidae) at various angles and spacings against three predaceous coccinellids, Harmonia axyridis, Coccinella septempunctata and Hippodamia variegata (Coleoptera: Coccinellidae).
BACKGROUND
Paratrioza sinica is a major pest of wolfberry (Lycium barbarum). Coccinellids can effectively control various developmental stages of P. sinica but not the stalked egg. To investigate the protective role of egg stalks against the predaceous coccinellids Harmonia axyridis, Coccinella septempunctata and Hippodamia variegata, we studied the functional responses to, and effects of, two factors: the angle between the egg stalk and the leaf plane, and the spacing between egg stalks.


RESULTS
The searching rate, handling time and theoretical maximum egg consumption of H. variegata were optimal among the three ladybug species. Egg consumption by coccinellids was maximum and minimum at stalk angles of 0° and 90°, respectively. The average reduction in the rate of egg consumption when the stalk angle was 90° relative to 0° was significantly smaller for larvae of coccinellids compared with adults, and for H. variegata compared with the other two species. Optimal spacing of eggs for consumption by predators varied with the predator species and their developmental stage, and was close to the body length of the predators.


CONCLUSION
The egg stalk serves as a physical protection against predators. The evolutionary selective advantage of the egg stalk in providing protection against predators requires more attention. Appropriate selection of predators and irrigation strategies may improve control of P. sinica. © 2017 Society of Chemical Industry.