## 2 Materials and Methods
### Y-Tube Ofractometer Behavioral Experiments  
The olfactory response of _A. melinus_ to host-associated cues was tested using a glass Y-tube olfactometer purchased from Volatile Collection Systems Co LLC (Gainesville, FL, USA). The Y-tube olfactometer design was similar to that described in [19] with slight modifications for the purpose of our research. Briefly, the Y-tube olfactometer consisted of a central tube (2.5 cm diameter, 15 cm long) and two lateral arms (2.5 cm diameter, 11 cm arm's length) with ground glass fittings through which humidified air passed (0.5 mL/sec through each arm, controlled by up-stream flow meters). Each arm was connected to an extended glass tube (2 cm diameter, 6 cm long). The extended glass tube with the mesh barrier prevented the insects from escaping. The air was filtered with activated carbon traps, then passed through a chamber into each fruit, then VOCs and insects could be introduced. The air passed through the olfactometer and then the system was left to stabilise for 15 min prior to use. Olfactometer studies were carried out at 25 \(\pm\) 1 \({}^{\circ}\)C (45-55% RH) in a room illuminated with overhead daylight fluorescent tubes. A light was placed over the Y-tube olfactometer, and the surrounding area (around and below) was shrouded with white paper to block out any visual cues. _A. melinus_ is an ectoparasitoid, so pupae could be isolated from host and host plant material withoutdisrupting their development. From adult emergence until their use for bioassays, parasitoids were held in tubes (1 cm diameter, 4 cm length) and droplets of honey were provided throughout their lives. All wasps used for the bioassays were naive females without any previous contact with infested or non-infested host fruit. After placing parasitoids in the conditioning vial for a day, wasps were removed and placed in an empty container. On the day of bioassay, female wasps were isolated and held individually in glass vials with a drop of honey until tested. A total of 40 replicates (individual _A. melinus_) were conducted for each of the three citrus fruit species, and the four tested dosages of the synthetic VOCs. For each bioassay, a single female wasp was introduced into the central arm tube of the olfactometer. Once the wasp had reached the point where the arm divides (i.e., when the wasp reached a position to make a choice), a timer was started. If the parasitoid remained stationary for two minutes, it was considered as unresponsive. It was then excluded from the study and substituted with another one. The olfactometer was reversed after half of the wasps in each replicate had been tested. After all ten parasitoids were assayed, the odour sources were removed, and the apparatus was cleaned with water and acetone, then dried and heated in an oven at 80 \({}^{\circ}\)C for at least half an hour between replicates. Overnight between treatments, new sources were introduced into the aeration chambers, and a further replicate of ten parasitoids was tested. For bioassays involving fruit, fresh and ripe fruit samples were tested to reduce the variation in volatile emissions between replicates. To understand whether infested citrus fruit is attractive to _A. melinus_, at the first stage, mated females were allowed to choose between non-infested or infested fruit samples for each citrus species. A wasp was considered to have chosen a cue when it remained in the same chamber for at least 20 s, actively searching for a host. The bioassay replicate was considered complete when the wasp left the chamber. However, if wasps are unresponsive after two minutes in the system, they were eliminated from the study. For assessment of the attraction of synthetic VOCs, two different concentrations (10 and 20 \(\upmu\)L/mL) of p-limonene and \(\beta\)-ocimene (p-limonene purity 97%, 98% EE (GLC) Sigma-Aldrich, and \(\beta\)-ocimene purity \(\geq\) 90% Toronto Research Chemicals, North York, ON, Canada) were dissolved in hexane.