BEHAVIORAL ECOLOGY OF MYIOPHARUS-DORYPHORAE (RILEY) AND MYIOPHARUS-ABERRANS (TOWNSEND), TACHINID PARASITOIDS OF THE COLORADO POTATO BEETLE

The behavior of Myiopharus doryphorae and M. aberrans, North American tachinid parasitoids of the Colorado potato beetle, was recorded under field and laboratory conditions throughout three growing seasons in w estern Massachusetts. Eight common behaviors associated with resting, searching, feeding, and larviposition were distinguished, which togeth er accounted for nearly all daytime activity of the females of both ta chinids. Several of these behaviors, and in particular larviposition, were closely related to temperature but differed between species. A se quence of five defensive behaviors by the different larval stages of t he Colorado potato beetle prevented larviposition in 49% of resisted a ttempts and perhaps one-fourth of total larviposition attempts by Myio pharus species, yet both parasitoids were highly successful in allocat ing their progeny during most of the summer. Second- and third-instar beetle larvae were least effective in resisting larviposition. Females of both Myiopharus species actively guarded recently parasitized host s from other Myiopharus females for a period of several minutes after larviposition during the last month of the growing season when second- and third-instar Colorado potato beetle larvae were most scarce. Labo ratory studies based on the field observation that female M. aberrans doggedly pursued circum-diapausing adult beetles led to the first reco rded account of M. aberrans larvipositing in adult hosts. Flies gained access to a beetle's vulnerable abdominal dorsum at the instant it li fted its elytra to initiate flight. The late-season switch of M. aberr ans to adult Colorado potato beetles contributed to a seasonal sequenc e of larviposition-related behaviors concordant with prevailing host d ensities, which should lend complementarity to M. doryphorae and M. ab errans as biological controls of pest populations.