Juli Carrillo

Over the past 30 years, the potential of silicon to improve crop plant performance hasgained increasing recognition in the field of plant science. Silicon may be a key tool to guardcrop production against uncertain future growing conditions by improving crop toleranceto abiotic and biotic stressors. In this thesis, I take recent advances in our understandingof silicon ecology and extend them into cereal crops, testing for the presence of rapid (24 hour) silicification in common Canadian crops after defence induction events, includingherbivory, and used a genome-wide association study to identify potential genetic markersassociated with high silicon content. We found that overall, simulated herbivory, but notcricket herbivory, increased silicon leaf content. However, at the species level, we found nosignificant increases in silicon content in response to herbivory treatments. This may be dueto a silicon-poor soil environment or could reflect the effect of herbivore identity on specificdefensive outcomes. In our genetic analysis, we found no genetic markers with significantassociations to silicon content but did find a marker that had a significant correlation withmanganese content. Our limited results may reflect the polygenic nature of silicon contentin plants, or strong environmental effects. Future studies could build upon our results bydeveloping a mapping population using genotypes we identified as representing the extremesof silicon content. Applications of silicon research into crop production techniques are stilllimited by crucial gaps in our understanding of how ecology and genetics control siliconuptake, but this work provides yet another steppingstone towards the broader adoption ofsilicon into agricultural systems.

View record

As agricultural intensification accelerates around the world, the proportion of natural habitat in and around agricultural ecosystems has decreased. Restoration of these habitats may lead to an increase in the abundance and diversity of natural enemy insects that play a key role in agricultural pest control. However, these effects have been shown to be system-specific and depend upon climatic conditions, landscape structure, the local species pool, etc. To evaluate the response of the insect community to semi-natural habitat enhancement, I surveyed insects in the Lower Mainland region of British Columbia, Canada across two growing seasons and in four distinct types of restored on-farm habitat (differently managed hedgerows and grassland set-asides). I sampled insects using a variety of trapping techniques to obtain metrics of diversity and abundance and subsequently identified them to a taxonomic level where a functional guild could be assigned (family in most cases and lower when possible).I found that habitat type mostly did not determine the overall and intra-guild family diversity of arthropods. Grassland set-asides designed to support pollinators supported a higher abundance of ground-dwelling natural enemy arthropods and pests compared to unenhanced fields. I was better able to detect differences among habitat types in more taxonomically resolved groups. Grassland set-asides supported a greater abundance and diversity of predatory carabid beetle genera compared to control fields. Both hedgerow types showed higher average abundances of Drosophila suzukii, an invasive pest of fruit crops in British Columbia, compared to unenhanced grassy margins. These findings indicate that some economically important taxa (predaceous ground beetles, invasive Drosophila suzukii) respond strongly to semi-natural habitat elements in agro-ecosystems. However, it is possible that broad-level taxonomic analyses of these responses are not sufficiently sensitive to quantify these responses. It is likely that focusing biodiversity studies on a few highly resolved and representative taxa will yield more insightful conclusions. Further research will be required to determine if these changes in the insect community driven by semi-natural habitat restoration will impact levels of pest pressure and biocontrol within cropped fields.

View record

Pollinators rely on floral resources for food and reproduction. They require access to sufficient forage throughout their active periods, yet agricultural intensification alters the landscape causing a loss of essential floral resources. To increase pollinator abundance for pollination services, land managers can incorporate floral resources through habitat amendments, including intercrops, floral strips, and hedgerows. Using the UBC farm as a case study, I first compared two floral strip types, a common cover crop blend of mixed ryegrass and crimson clover and the floral intercrop sweet alyssum, to experimentally investigate the abundance and diversity of pollinators attracted to each floral strip type within a kale production field. Secondly, I conducted an observational survey of four single flower species strips (borage, buckwheat, dill, and ryegrass with crimson clover) to determine potential suitability of these intercrops for larger-scale experimental trials. Finally, I conducted floral and bumble bee surveys over the growing season across the entirety of UBC Farm to examine the relationship between bumble bee foraging choice and the availability of floral resources to determine bumble bee preferences. Overall, I found that different floral resources attracted a different assemblage of pollinators. I found that within the kale production field, the common cover crop blend of rye/clover supported more species of Apidae (Hymenoptera), including (Bombus spp.), while sweet alyssum supported more Syrphidae (Diptera) species. The four single species flower strips attracted insects in the genera (Hymenoptera) Apis, Bombus, Dolichovespula, Halictus, Polistes; (Coleoptera) Coccinella, Harmonia, Rhagonycha; (Diptera) Eristalis, Toxomerus. Bumble bees visited Dahlia pinnata, Rosa nutkana, Symphoricarpos albus, Rubus parviflorus, and Phacelia tanacetifolia more often than expected given the availability of the flowers. Bumble bees visited Phacelia tanacetifolia, Trifolium incarnatum, and Symphoricarpus albus over consecutive sampling sessions. Trifolium pratense, Trifolium repens, and Taraxacum officinale bloomed the entire study period and bumble bees visited them but never beyond the null expectation. My thesis provides insight into floral species favoured by pollinators in agricultural environments, which can aid in future land management decisions and conservation efforts to ensure that pollinators have access to consistent, reliable, and plentiful forage throughout their active periods.

View record

Insect pests are one of the main detrimental factors for food production systems partially because of the substantial inputs used to control their damage. Pest control typically considers the biology, incidence, and distribution of pest species, and can be improved through understanding the underlying ecology of plant—pest—predator interactions. Integrated pest management programs which include the introduction of insect natural enemies for biological control can supplement the control efforts of pesticide application. However, pesticides can directly affect the survival and performance of beneficial predaceous insects, decreasing their efficacy. Conversely, pesticides may also increase the susceptibility of insects, promoting the predatory performance of their natural enemies. I carried out a series of bioassays in tomato (Solanum lycopersicum L.) to determine the combined effects of a presumed insecticidal botanical extract, karanja oil, on the survival and performance of a pest insect, greenhouse whitefly Trialeurodes vaporariorum (Westwood), and two of its natural enemies, the whitefly parasitic wasp Encarsia formosa (Gahan) and the ladybeetle Delphastus catalinae (Horn). We found a strong negative correlation between increasing concentrations of karanja oil and the survival of whitefly adults and nymphs. The highest concentration (3% v/v%) killed 80% of the whitefly adults and nymphs, whereas the lowest concentration (0.5% v/v%) was lethal to more than 60% of the whiteflies. Karanja oil had a residual negative effect on the immature stages of the whiteflies, and did not interrupt the parasitic performance rate by E. formosa. Karanja oil was lethal to both predators and parasitoids when it was applied directly to them, suggesting that in integrated management programs, natural enemies should be introduced after the application of these botanical derivatives. There was no evidence of plant phytotoxicity on tomato plants at the concentrations of karanja oil that we applied.

View record

Drosophila suzukii is an invasive fruit fly of agricultural concern as it is able to oviposit in ripening and fresh fruit. Olfactory signals in the form of volatile organic compounds (VOCs) may reduce D. suzukii attraction to hosts and decrease survival, but it is unknown how the efficacy of VOCs varies across D. suzukii life stages and how VOCs interact with cultural and biological controls. Peppermint essential oil and fresh peppermint (Mentha x piperita) produce VOCs and recent studies have shown peppermint essential oil to be effective at repelling adult D. suzukii. First, through a series of laboratory bioassays, we evaluated the joint effects of peppermint VOCs on D. suzukii survival and the survival of and parasitism rates by a pupal parasitoid wasp, Pachycrepoideus vindemmiae. We determined whether exposure to peppermint VOCs at the pupal stage reduced adult emergence, and whether this depended on environmental conditions (i.e. soil moisture). Then, we evaluated whether exposure to peppermint VOCs reduced or enhanced parasitism by the pupal parasitoid and whether this depended on the timing of peppermint VOC exposure (i.e. before, during, or after parasitism). Second, we used a intercropping field trial to determine whether intercropping with peppermint plants could reduce D. suzukii infestation in dropped blueberries. We used weekly baited fruit cages to monitor D. suzukii infestation and herbivory by other pests in both a peppermint intercrop and a conventional ryegrass/white clover mix. In our laboratory bioassays, we found that exposure to higher concentrations of peppermint VOCs reduced D. suzukii emergence under moist soil conditions and that this was similar to dry soil with no peppermint exposure. Peppermint VOCs were toxic to adult P. vindemmiae, but developing P. vindemmiae were unaffected by peppermint VOC exposure. In our field experiment, we found low D. suzukii infestations in both intercropping treatments. However we observed increased dropped fruit consumption by slugs, ground beetles and wasps, reducing D. suzukii host sites. Growers may utilize targeted peppermint VOC exposure or intercropping with peppermint to reduce D. suzukii infestation however, this could negatively impact populations of P. vindemmiae dependent on the timing of application.

View record