Gall wasp biocontrol of invasive Acacia longifolia: implications of strong bottom‐up effects

Abstract

Abstract. The population dynamics of insect herbivore biocontrol agents is central to the successful control of invasive weeds. Although the importance of agent population dynamics is recognized, it is rarely considered in assessments of the biocontrol potential of herbivore agents. Herbivore insect population dynamics are influenced by a combination of top-down effects from natural enemies, bottom-up effects from plant resource availability (resource quality and quantity), and potential interactions between these effects. To better understand the tri-trophic interactions that are likely to determine biocontrol success in a host plant-gall wasp-parasitoid system, the relative importance of top-down and bottom-up effects for the survival of a herbivore biocontrol agent (Trichilogaster acaciaelongifoliae), on two Acacia host plants in their native range, was estimated using path analysis. On both host plants, there was a strong positive relationship between gall mass per chamber and gall wasp survival and a strong negative relationship between gall mass per chamber and gall parasitism, with parasitoids being less common in large than small galls. There was, however, no significant correlation between parasitism and gall wasp survival and, therefore, no evidence for top-down effects in this system. Strong bottom-up effects of host plant resources on both gall wasp survival and gall parasitism have implications for the spatio-temporal variability of biocontrol success. Such variation should be considered in pre-release assessments and post-release monitoring of gall wasps used as herbivore biocontrol agents.

Measuring continuous compositional change using decline and decay in zeta diversity

“…These results are consistent with the expected ecological interpretation of inquilines as generalist herbivores opportunistically inhabiting the fleshy galls (and a strongly stochastic basis for the frequency with which they interact with different gall wasp species), compared with the host‐specific relationships between gall wasps and parasitoids (Henriksen et al. , ).…”

“…For inquilines the rate at which interactions were retained increases and then drops sharply from the third order, whereas it increases and drops gradually from order six for interactions involving parasitoids. These results are consistent with the expected ecological interpretation of inquilines as generalist herbivores opportunistically inhabiting the fleshy galls (and a strongly stochastic basis for the frequency with which they interact with different gall wasp species), compared with the host-specific relationships between gall wasps and parasitoids (Henriksen et al 2017(Henriksen et al , 2019.…”

The effect of network size and sampling completeness in depauperate networks

“…To identify species and interactions in the host–parasitoid network at each site, galls were reared in the laboratory and emerged individuals were identified to family, or lower taxonomic level when possible, and grouped into morpho‐species and trophic levels (following the methods of Henriksen et al., ). Only individuals from families known to be specifically associated with gall tissue were used in the analysis.…”

“…Trichilogaster larvae are attacked by a range of parasitoids and gall inquilines (that feed on gall tissue without consuming the gallformer) (Henriksen, Chapple, Chown, & McGeoch, 2017;Noble, 1940Noble, , 1941. Parasitoids of the Trichilogaster gall wasps have a 1:1 impact on the gall wasp individuals; that is, one gall wasp is consumed for every parasitoid individual emerged (Noble, 1940(Noble, , 1941.…”

Can Niche Dynamics and Distribution Modeling Predict the Success of Invasive Species Management Using Biocontrol? Insights From Acacia longifolia in Portugal

“…A database of A. longifolia and T. acaciaelongifoliae occurrence records was compiled from the Global Biodiversity Information Facility 1 , Atlas of Living Australia 2 , South Australian Museum 3 provided upon request by Doctor Peter Hudson, Australian National Insect Collection 4 provided upon request by Doctor Juanita Rodriguez, Invasive Plants in Portugal -Invasoras.pt 5 (Marchante et al, 2017), Southern Africa Plant Invaders Atlas (Henderson, 1999), literature references (Dennill, 1985(Dennill, , 1987Prinsloo and Neser, 2007;Lado, 2008;Henriksen et al, 2017Henriksen et al, , 2019; and data provided by authors and collaborators (see section "acknowledgments"). Data collection for A. longifolia and T. acaciaelongifoliae was independent and no records were shared among the two datasets.…”