Simple SummarySenotainia tricuspisis a dipterian endoparasitoid of the honey bee. It is responsible for the severe damage (called senotainiosis) of apiaries in several European, North African and Middle Eastern countries. Despite the availability of data on the infestation percentages and the increasingly growing awareness of the senotainiosis damage in beekeeping, the aggression and parasitization behavior ofS. tricuspistowardsA. melliferaremains poorly investigated. In this study, a description of parasitisation behavior, as well as data on the pupation and emergence ofS. tricuspisin an apiary in the province of Pisa (Central Italy), is provided. The categories of aggression, beecatcher, chase and parasitization in the attack behavior ofS. tricuspistoward western honey bees were identified and described. Moreover, the daily temporal pattern of the number of aggressions showed two main peaks: one during the morning hours and one in the afternoon. Data on the sinking depth of larvae and successful pupation allowed us to hypothesize that mulch and/or minimum soil tillage could prevent severe senotainiosis in apiaries.AbstractSenotainia tricuspis(Meigen, 1838) is a Sarcophagid dipteran endoparasitoid ofApis melliferaL., and myiasis, caused by this fly, is reported in several European, North African and Middle Eastern countries. Nevertheless, very little knowledge concerning the aggression and parasitisation behavior ofS. tricuspistowardA. melliferais available in the scientific literature, and the temporal pattern of aggression remains unclear. The aim of this investigation was to describe the aggressive behavior ofS. tricuspisand to provide data on pupation and adult emergence in order to identify further tools for the control of senotainiosis in beekeeping. Data were collected in an apiary in Pisa province (Tuscany, Italy), where observations of aggressive behavior were conducted indirectly by using a VHS camera and also directly by an observer. Four behavioral categories of the attack were described. A total of 55 aggressions, 21 beecatchers, 104 chases and 6 parasitization events were recorded with the camera. Slow-motion recording analyses of the parasitization episodes resulted in contact of at least 1/6 s between the parasitoid and the host. Through four days of direct observations, a total of 1633 aggression events were recorded. The daily temporal pattern of the number of aggressions showed two main peaks: one during the morning hours (i.e., from 10:00 to 11:00) and one in the afternoon (i.e., from 15:00 to 17:00). The morphometric data on the first-instars ofS. tricuspisallowed us to hypothesize a penetration in the bee through its prothoracic spiracle as a modality of entrance in the host body. Third-instars successfully pupate when sinking in topsoil or clay soil, and adults emerge when left to a 4 °C overwintering period of six months. Furthermore, the high mortality rate of those larvae that did not sink and did not pupate successfully suggests that reaching a certain depth in the soil is a determining factor for larvae survival and that mulch and/or minimum soil tillage could prevent severe senotainiosis in apiaries.