Unravelling chemical cues used by Diachasmimorpha longicaudata (Hymenoptera: Braconidae) during host search

NUSSENBAUM, A.L.; BACHMANN, G.E.; SEGURA, D. F.; DEVESCOVI, F; FERNÁNDEZ, PATRICIA C.

Bogotá

Congreso; 10a Reunión del grupo de trabajo moscas de la fruta del hemisferio occidental; 2020

Instituto Colombiano Agropecuario ICA

Diachasmimorpha longicaudata is one of the most commonly used biocontrol agents against Tephritidae fruit fly pests. Females parasitize their hosts during the larval stage when they are still feeding inside the fruit. In order to locate infested fruit, female wasps use semiochemicals from the microhabitat of the host. Using a stationary olfactometer (no air flux), previous studies have shown that oranges infested with Ceratitis capitata (Diptera: Tephritidae) larvae, infested oranges from which all larvae had exited, rotten (non-infested) oranges, and oranges infected by the fungus Penicillum spp. were preferred by female parasitoids when offered in dual choice tests with healthy oranges (control). Our objective was to confirm attraction to these sources using a dynamic Y-tube olfactometer (with air flux) and to identify the chemical compounds responsible for the attraction of D. longicaudata. Results showed that, similar to what was found in stationary olfactometers, the orientation behavior of D. longicaudata towards their hosts involved air-borne compounds, and that the activity of larvae inside the fruit, the process of decomposition, and the presence of Penicillum spp., trigger attraction in females. We then collected the volatile compounds originated by these oranges by means of dynamic head-space sampling using HayeSep-Q traps. After eluting with methylene chloride, the samples were used in GC-EAD to determine which compounds generate a electrophysiological response in the female antenna. The samples were also analyzed by GC-MS using the NIST library and Kovats index in order to identify these specific compounds. Qualitative differences were found among the different type of oranges, but only 1-octanol, terpinen-4-ol, dodecanal and an unknown compound were antenally active and shared by all but the healthy oranges. Many other compounds triggered electrophysiological responses but were shared by some of the treatments or were exclusively found in one of the treatments. Standard compounds will be used in further GC-EAD analyses and bioassays in Y-tube olfactometers in search of an effective bait for monitoring parasitoid populations and to study the possibility to pull parasitoids into fruit crops under biological control programs.