Interaction between the parasitoid Mallophora ruficauda (Diptera: Asilidae) and its host Cyclocephala signaticollis (Coleoptera: Scarabaeidae): a possible case of pheromone exploitation.

GROBA, H.F.; CASTELO, M.K.

Palermo, Italia

Conferencia; Conference on “Behavioural Ecology of Insect Parasitoids: a perspective”; 2009

European Science Foundation

<!-- /* Font Definitions */ @font-face {font-family:Calibri; mso-font-alt:"Century Gothic"; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin-top:0pt; margin-right:0pt; margin-bottom:10.0pt; margin-left:0pt; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibri; mso-fareast-font-family:Calibri; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} @page Section1 {size:612.0pt 792.0pt; margin:113.4pt 70.9pt 113.4pt 70.9pt; mso-header-margin:35.45pt; mso-footer-margin:35.45pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Mallophora ruficauda is a robber-fly endemic to the Pampas region of Argentina. As an adult, its feeds mainly on foraging honeybees and other hymenopterans, and as larva is a koinobiont solitary ectoparasitoids of third instar Scarabaeidae larvae (white grubs), particularly Cyclocephala signaticollis. This parasitoid has a shared host-searching strategy between the female and the larva. Females oviposit egg-clutches away from the host on tall grasses, and after hatching, first instar larvae are dispersed by the wind, falling to the ground. Once in the soil, larvae moult to next instar and acquire the host-searching capacity. The host location is mediated by chemical cues produced by the host, specifically in the posterior half of the body, however, it is unknown the source of infochemicals generation. The aims of this study were to identify the body structure of the host that produces the infochemicals implicated in the host-searching of M. ruficauda larva, and to determine if these substances play an ecological role among C. signaticollis individuals. In order to know the precise anatomical origin of the infochemicals that trigger the searching behavior of M. ruficauda larva, and a possible conspecific behavior of C. signaticollis, we performed behavioural experiments of olfactometry to analyze the orientation responses of the individuals to different stimuli extracted from posterior body parts of the white grubs. We determined that extracts obtained from fermentation chamber evoked behavioural responses both in M. ruficauda as in C. signaticollis. We found that C. signaticollis showed a positive orientation towards this stimulus, suggesting the existence of possible pheromone that explains aggregative behavior of this species in the field. Furthermore, this stimulus also evoked positive orientation of M. ruficauda, suggesting that this parasitoid uses for locate its host an infochemical that also mediates the conspecific interaction among C. signaticollis individuals.