Over two decades ago, an intercropping strategy was developed that received critical acclaim for synergizing food security with ecosystem resilience in smallholder farming. The push–pull strategy reportedly suppresses lepidopteran pests in maize through a combination of a repellent intercrop (push), commonly Desmodium spp., and an attractive, border crop (pull). Key in the system is the intercrop’s constitutive release of volatile terpenoids that repel herbivores. However, the earlier described volatile terpenoids were not detectable in the headspace of Desmodium, and only minimally upon herbivory. This was independent of soil type, microbiome composition, and whether collections were made in the laboratory or in the field. Furthermore, in oviposition choice tests in a wind tunnel, maize with or without an odor background of Desmodium was equally attractive for the invasive pest Spodoptera frugiperda. In search of an alternative mechanism, we found that neonate larvae strongly preferred Desmodium over maize. However, their development stagnated and no larva survived. In addition, older larvae were frequently seen impaled and immobilized by the dense network of silica-fortified, non-glandular trichomes. Thus, our data suggest that Desmodium may act through intercepting and decimating dispersing larval offspring rather than adult deterrence. As a hallmark of sustainable pest control, maize–Desmodium push–pull intercropping has inspired countless efforts to emulate stimulo-deterrent diversion in other cropping systems. However, detailed knowledge of the actual mechanisms is required to rationally improve the strategy, and translate the concept to other cropping systems.

Insects use sensitive olfactory systems to detect relevant host volatiles and avoid unsuitable hosts in a complex environmental odor landscape. Insects with short lifespans, such as gall midges (Diptera: Cecidomyiidae), are under strong selection pressure to detect and locate suitable hosts for their offspring in a short period of time. Ephemeral gall midges constitute excellent models for investigating the role of olfaction in host choice, host shift, and speciation. Midges mate near their site of emergence and females migrate in order to locate hosts for oviposition, thus females are expected to be more responsive to olfactory cues emitted by the host compared to males. In this study, we explored the correlation between host choice and the function of the peripheral olfactory system in 12 species of gall midges, including species with close phylogenetic relationships that use widely different host plants and more distantly related gall midge species that use similar hosts. We tested the antennal responses of males and females of the 12 species to a blend of 45 known insect attractants using coupled gas chromatographic-electroantennographic detection. When the species-specific response profiles of the gall midges were compared to a newly generated molecular-based phylogeny, we found they responded to the compounds in a sex- and species-specific manner. We found the physiological response profiles of species that use annual host plants, and thus have to locate their host every season, are similar for species with similar hosts despite large phylogenetic distances. In addition, we found closely related species with perennial hosts demonstrated odor response profiles that were consistent with their phylogenetic history. The ecology of the gall midges affects the tuning of the peripheral olfactory system, which in turn demonstrates a correlation between olfaction and speciation in the context of host use.

The chemical signatures emitted by fungal substrates are key components for mycophagous insects in the search for food source or for suitable oviposition sites. These volatiles are usually emitted by the fruiting bodies and mycelia. The volatiles attract fungivorous insects, like flowers attract pollinators; certain flowers mimic the shape of mushroom fruiting bodies and even produce a typical mushroom odor to exploit on fungus-insect mutualism. There are numerous insects which are mycophagous or eat fungi additionally, but only a few are considered a threat in agriculture. Lycoriella ingenua is one of the most serious pests in mushroom cultivation worldwide. Here we attempt to examine the role of environmental volatiles upon behavioral oviposition preference. In two-choice bioassays, fungus gnats preferred uncolonized compost compared to colonized compost but preferred colonized compost against nothing. However, when colonized compost was paired against distilled water, no significant choice was observed. The comparison of fresh casing material and mycelium colonized casing material resulted in no significant preference. From colonized compost headspace, three antennally active volatiles were isolated by gas chromatography coupled with electroantennography and subsequently identified with gas chromatography coupled mass spectrometry as 1-hepten-3-ol, 3-octanone and 1-octen-3-ol. In behavioral assays the addition of said synthetic volatiles to uncolonized compost separately and in combination to mimic colonized compost resulted in avoidance. We thus partially elucidate the role of fungal volatiles in the habitat seeking behavior of Lycoriella ingenua.

The box tree moth, Cydalima perspectalis, is an invasive pest in Europe causing damage on Buxus species. In this study, we aimed to develop a “bisexual” lure to attract both female and male moths. Based on a previous screening bioassay we tested methyl salicylate, phenylacetaldehyde and eugenol as potential attractants in different combinations. The trapping results showed that both binary and ternary blends attracted male and female moths. Catches with these blends were comparable to catches with the synthetic pheromone. Subsequently we carried out single sensillum recordings, which proved the peripheral detection of the above-mentioned compounds on male and female antennae. To identify synergistic flower volatiles, which can be also attractive and can increase the trap capture, we collected flower headspace volatiles from 12 different flowering plant species. Several components of the floral scents evoked good responses from antennae of both females and males in gas chromatography-electroantennographic detection. The most active components were tentatively identified by gas chromatography coupled mass spectrometry as benzaldehyde, cis-ß-ocimene, (±)-linalool and phenethyl alcohol. These selected compounds in combination did not increase significantly the trap capture compared to the methyl salicylate- phenyacetaldehyde blend. Based on these results we discovered the first attractive blend, which was able to attract both adult male and female C. perspectalis in field conditions. These results will yield a good basis for the optimization and development of a practically usable bisexual lure against this invasive pest.

The box tree moth (Cydalima perspectalis Walker) is an invasive species in Europe causing severe damage both in natural and ornamental boxwood (Buxus spp.) vegetation. Pest management tactics are often based on the use of chemical insecticides, whereas environmentally-friendly control solutions are not available against this insect. The application of essential oils may provide effective protection against oviposition and subsequent larval damage. Oviposition deterrence of cinnamon, eucalyptus and lavender essential oils was tested on female C. perspectalis in behavioural bioassays. Our results indicate that all the studied essential oils may be adequate deterrents; however, cinnamon oil exhibited the strongest effect. To determine the physiologically active compounds in the headspace of the essential oils, gas chromatography coupled with electroantennography recordings were performed in parallel with gas chromatography-mass spectrometry to identify the volatile constituents. In addition, the release rates of various components from vial-wick dispensers were measured during the oviposition bioassay. These results may serve as a basis for the development of a practical and insecticide-free plant protection method against this invasive moth species.