Addition of nectar sources affects a parasitoid community without improving pest suppression

Abstract

A life-table approach was used to test the effect of adding flowering buckwheat to leek plots on mortality and estimated population growth of the invasive leek moth, Acrolepiopsis assectella. This approach was used to estimate the benefits of nectar provisioning on multiple members of the leek moth’s parasitoid complex, and the impact of parasitism on the pest’s predicted population growth rate. Addition of buckwheat to leek plots shifted the relative abundance of different larval and pupal parasitoid species but did not increase or decrease parasitism levels or their population-level impact on the leek moth. The life-table analysis demonstrated that parasitoids reduced the estimated population growth rate of the leek moth by up to 72%, which far exceeds similar estimates from its native range. Parasitoids found to contribute to leek moth mortality were Itoplectis conquisitor, Conura albifrons and the biological control agent Diadromus pulchellus. In addition, Gambrus ultimus, Scambus calobatus, and Habrobracon sp. are reported here developing on A. assectella for the first time. This study reinforces the hypothesis that the addition of nectar resources to agricultural systems may not have straightforward positive effects and can favour some natural enemies over others, but may not have any overall impact on pest suppression.

Trait‐based characterisation of parasitoid wasp communities in natural and agricultural areas

“…Alternatively, if adult parasitoids indeed live longer in their natural habitats, they may simply have a longer time window available for sugar feeding than the orchard parasitoids. In agreement with our findings, planting of nectar‐rich plants in crop plots were found to change the species composition (Miall et al, 2020) and within‐plot distribution (Kishinevsky et al, 2017) of resident parasitoid communities, possibly by attracting nectar‐dependent species.…”

Flowering Plants and Entomophagous Arthropods in the Agricultural Landscape: A Practise-Oriented Summary of a Complex Relationship

“…For example, sugar and flower diets increased the adult longevity of the two spotted lady beetle Adalia bipunctata whereas the fecundity was nil on all non-prey diets [62] . In some predators, floral diets or sugar sources do not support juvenile molting [62,71,72] . Also, there are studies reporting that the addition of nectar or pollen sources affects the diversity and population community of many natural enemies without increasing pest suppression [73] .…”

The parasitoid complex of diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), in Canada: impact and status

“…To construct the life tables, mortality rates calculated from field data were applied to a hypothetical cohort of 1000 eggs. Calculation of life table parameters was in accordance with Miall et al (2021) and is summarised as follows: apparent mortality (q x ) due to known (e.g., parasitism) or unknown biotic and abiotic factors was calculated as the ratio of the number of individuals dying in a stage (d x ) to the number entering the stage (l x ). Real mortality (r x ) was calculated as the ratio of the number of individuals dying in a particular life stage to the initial starting number at the beginning of the study (1000).…”