Jerking in predaceous mites (Acari: Phytoseiidae) with emphasis on larvae.

ABSTRACT

Jerking, a behavior involving a pronounced and often repeated lunging of the body, was studied in larvae among seven species of phytoseiid mites, Euseius finlandicus, Galendromus occidentalis, Neoseiulus californicus, Neoseulus fallacis, Phytoseiulus macropilis, Phytoseiulus persimilis and Typhlodromus pyri, and in the nymphal stages of N. fallacis. This behavior was observed in larvae of six of the seven species and in all active immature stages of N. fallacis. Jerking was usually triggered by direct contact with a con- or heterospecific mite, although jerking occurred occasionally without direct contact in N. fallacis larvae. The larval jerking tendency (the mean fraction of contacts resulting in jerking) of a species was significantly correlated with a tendency to congregate with conspecifics. Congregated larvae often probed their immediate area and each other with the front legs, repeatedly jerking in response to contact with neighboring larvae. Species with larvae having higher jerking tendencies also jerked more repeatedly per jerking event. Among species, there was no consistent relationship between jerking tendency and larval age. Larvae of N. fallacis had a higher tendency to jerk than protonymphs and deutonymphs, and they had both the highest jerking and congregating tendencies among larvae of all species studied. An individual was more likely to jerk when approached by another mite than when it initiated contact, and when observed in N. fallacis larvae that initiated contact, jerking was sometimes aggressive. Jerking N. fallacis larvae experienced fewer and shorter periods of probing by the mouthparts and fewer attacks from cannibalistic adult females than anesthetized larvae that were unable to jerk.