Biological Control Success of a Pasture Pest: Has Its Parasitoid Lost Its Functional Mojo?

Federico Tomasetto,Paula Casanovas,Stephen L Goldson,Samuel N Brandt

doi:10.3389/fevo.2018.00215

Federico Tomasetto, Paula Casanovas + Show 2 more

Open Access

https://doi.org/10.3389/fevo.2018.00215

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Abstract

Sustainable and integrated pest management often involves insect parasitoids. However, the effectiveness of parasitoids biocontrol has often failed, frequently for obscure reasons. A parasitoid’s success is partly due to its behavioral response to pest density, i.e. its consumer functional response. For many years in New Zealand, a braconid parasitoid, Microctonus hyperodae successfully suppressed a severe ryegrass weevil pest, Listronotus bonariensis. However, there is now evidence that this has severely declined, but that the extent of decline can depend on the pasture species. Here, we tested whether the current functional responses of M. hyperodae to L. bonarensis in two of the most common New Zealand pasture grasses (Lolium multiflorum and L. perenne) reflect observed differences in field parasitism and whether this functional response has changed over time. Our analysis involved data both from 1993 and 2018. We found a type I functional response in L. multiflorum in both years, but the slope of the relationship declined over time. There was no evidence for any type of functional response in L. perenne. This lack of response in the L. perenne coincided with consistently found lower parasitism rates on this host plant than in L. multiflorum; both in the field and laboratory. Here, we found that apparently declining searching efficiency was correlated with the decline in parasitism. This observation supports the hypothesis that parasitism decline could be the result of evolution of resistance based on enhanced evasive behaviour by L. bonariensis.

Highlights

Adequate global nutritious and healthy food production in the face of growing human population will require sustainable pest management methods (Bruinsma, 2003; Ramankutty et al, 2018)
We found that parasitism rates were significantly higher in L. multiflorum than in L. perenne under the 2018 experimental conditions (p = 0.01, F = 7.8, df = 18; Figure 1A)
We found no evidence in the 2018 data of any functional response in the L. perenne treatment

Summary

Introduction

Adequate global nutritious and healthy food production in the face of growing human population will require sustainable pest management methods (Bruinsma, 2003; Ramankutty et al, 2018). Among the attributes thought to be related to the success of parasitoid biocontrol agents is the behavior of individual parasitoids in response to host density (Huffaker et al, 1971; Barlow et al, 1993; Berryman, 1999). Such behavior is called ‘consumer functional response’ and is defined as the relationship between the number of hosts attacked by a predator as a function of prey density (Solomon, 1949; Holling, 1959, 1966). The type III response is a sigmoid curve: as host density rises, the response initially accelerates due to the parasitoid becoming increasingly efficient at finding hosts (attack rate increases or handling time decreases) levels off under the influence of handling time or satiation (Berryman, 1999; Hassell, 2000)

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