Vespula germanica is a social wasp and an opportunistic predator. While foraging, these wasps learn and integrate different kinds of cues. They have successfully invaded many parts of the world, including native Nothofagus and Lophozonia forests located in the Andean-Patagonian region, where they forage on native arthropods. Perzelia arda, a lepidopteron defoliator of Lophozonia obliqua, uses the foliage to hide in and feed on. The purpose of this work is to study whether V. germanica use olfactory cues when foraging on P. arda. To do this, we used a Y-tube olfactometer and established three treatments to compare pairs of all combinations of stimuli (larvae, leaves with larval traces, and leaves without larval traces) and controls. Data were analysed via two developed models that showed decisions made by V. germanica and allowed to establish a scale of preferences between the stimuli. The analysis demonstrates that V. germanica wasps choose P. arda as larval prey and are capable of discriminating between the offered stimuli (deviance information criterion (DIC) null model = 873.97; DIC simple model = 84.5, n = 152). According to the preference scale, V. germanica preferred leaves with traces of larvae, suggesting its ability to associate these traces with the presence of the prey. This may be because, under natural conditions, larvae are never exposed outside their shelters of leaves and therefore V. germanica uses indirect signals. The presence of V. germanica foraging on P. arda highlights the flexible foraging behaviour of this wasp which may also act as a positive biological control, reducing lepidopteran populations.

Wheat bulb fly (WBF) larvae use chemotaxis to orientate towards host-plant root exudates. This study aimed to investigate the role of the primary plant metabolite carbon dioxide (CO2) in host-plant location by WBF. Arena based behavioural experiments were used to identify whether CO2 induced chemotaxis (directional movement in response to a chemical stimulus) or kinesis (non-directional movement in response to a stimulus) from WBF larvae. No chemotactic response was observed when larvae were presented to a point source of CO2. However, elevated levels of CO2 induced kinesis, with both track length and tortuosity (number of twists and turns in the movement path) increasing at elevated CO2 levels of 1000–2000 ppm, demonstrating increased searching behaviour. Soil emission of CO2 was quantified to compare soil levels with those identified as eliciting behavioural effects on the larvae. Samples removed from soil gave a mean CO2 concentration of 557 (±46) ppm, which is lower than the lowest concentration of CO2 found to induce a behavioural response and higher than the lowest CO2 concentration tested, which was found not to alter behaviour. It is proposed that increased CO2 concentrations in the soil act as a behavioural trigger, inducing intensive searching of an area by WBF larvae. This increases the likelihood of finding more host-specific identifiers, such as secondary metabolites when near a potential host-plant.