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

BACHMANN GUILLERMO E.; SEGURA DIEGO F.; DEVESCOVI FRANCISCO; FERNÁNDES PATRICIA C.; NUSSENBAUM ANA L.

Bogotá

Congreso; Americas Congress on Fruit Flies - X Meeting of Tephritid Workers of the Western Hemisphere; 2020

ICA

Diachasmimorpha longicaudata is one of the most commonly used biocontrol agentsagainst Tephritidae fruit fly pests. Females parasitize their hosts during the larval stage when theyare still feeding inside the fruit. In order to locate infested fruit, female wasps use semiochemicalsfrom the microhabitat of the host. Using a stationary olfactometer (no air flux), previous studieshave shown that oranges infested with Ceratitis capitata (Diptera: Tephritidae) larvae, infestedoranges from which all larvae had exited, rotten (non-infested) oranges, and oranges infected bythe fungus Penicillum spp. were preferred by female parasitoids when offered in dual choice testswith healthy oranges (control). Our objective was to confirm attraction to these sources using adynamic Y-tube olfactometer (with air flux) and to identify the chemical compounds responsiblefor the attraction of D. longicaudata. Results showed that, similar to what was found in stationaryolfactometers, the orientation behavior of D. longicaudata towards their hosts involved air-bornecompounds, and that the activity of larvae inside the fruit, the process of decomposition, and thepresence of Penicillum spp., trigger attraction in females. We then collected the volatile compoundsoriginated 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 whichcompounds generate a electrophysiological response in the female antenna. The samples were alsoanalyzed by GC-MS using the NIST library and Kovats index in order to identify these specificcompounds. 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 byall but the healthy oranges. Many other compounds triggered electrophysiological responses butwere shared by some of the treatments or were exclusively found in one of the treatments. Standardcompounds will be used in further GC-EAD analyses and bioassays in Y-tube olfactometers insearch of an effective bait for monitoring parasitoid populations and to study the possibility to pullparasitoids into fruit crops under biological control programs.