Low levels of cannibalism increase fitness in an herbaceous tortrix moth

Joncour

Pak

et al. 2019

Ecology

Asymmetric interactions among conspecifics can have diverse effects on population dynamics including stabilization, generation of cycles, and induction of chaotic fluctuations. A difficult challenge, however, is establishing the link between the impact of asymmetric interactions on life history and the consequences for population dynamics. The smaller tea tortrix, Adoxophyes honmai, is a good example. Larval instars differ dramatically in size and have a tendency for cannibalism, which suggests the potential for strong asymmetric interactions among instars. Yet whether these asymmetries have any role in generating the distinct single‐generation cycles observed in the field and laboratory is unclear. Here we report on the development of a new experimental approach to characterize the impact of asymmetric interactions on life history that can be directly embedded into stage‐structured population models. The experiments use donor‐replacement protocols in which focal individuals are challenged to complete their life cycles in competitive environments where the instar and density of the competitors are held constant. The experimentally derived interaction surface contains all the information about stage‐specific interactions and provides a straightforward framework for evaluating alternative ways of abstracting the interactions into traditional models of asymmetric competition. Working with the smaller tea tortrix, we found strong evidence of asymmetric interactions and identified critical “tipping points” in the competitive environment that strongly affected survival but not development. We incorporated the experimentally derived interaction surface into a stage‐structured population model and found that despite the strong impact that asymmetric interactions have on tea tortrix life history, they do not scale‐up to impact the predicted asymptotic population dynamics. Comparing these dynamics with two abstracted models of stage‐structured interactions revealed that while the quantitative details of the emergent dynamics depends on the shape of the interaction surface, the qualitative features, such as the emergence of single‐generation cycles and rapid synchronization of development among individuals, are pleasingly robust.

Section: Introductionmentioning

confidence: 87%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 91%

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Asymmetric interactions and their consequences for vital rates and dynamics: the smaller tea tortrix as a model system

Joncour

Pak

et al. 2019

Ecology

“…For example, susceptibility to parasitism and predation in insects are often instar specific (Benrey & Denno, 1997;Chau & Mackauer, 2000) and therefore larvae in targeted instars may interact with parasitoids and predators, but those in non-targeted instar stages might not. Similarly, cannibalism commonly occurs between different stages with larger stages cannibalizing smaller stages (Hopper, Crowley, & Kielman, 1996;Pereira, Agostinho, & Winemiller, 2017;Simpson, Joncour, & Nelson, 2018). Similarly, cannibalism commonly occurs between different stages with larger stages cannibalizing smaller stages (Hopper, Crowley, & Kielman, 1996;Pereira, Agostinho, & Winemiller, 2017;Simpson, Joncour, & Nelson, 2018).…”

Section: Introductionmentioning

confidence: 99%

Food quality effects on instar‐specific life histories of a holometabolous insect

Holmes

Lougheed

2020

Ecology and Evolution

Self Cite

1. It is a long-standing challenge to understand how changes in food resources impact consumer life history traits and, in turn, impact how organisms interact with their environment. To characterize food quality effects on life history, most studies follow organisms throughout their life cycle and quantify major life events, such as age at maturity or fecundity. From these studies, we know that food quality generally impacts body size, juvenile development, and life span. Importantly, throughout juvenile development, many organisms develop through several stages of growth that can have different interactions with their environment. For example, some parasitoids typically attack larger instars, whereas larval insect predators typically attack smaller instars. Interestingly, most studies lump all juvenile stages together, which ignores these ecological changes over juvenile development.2. We combine a cross-sectional experimental approach with a stage-structured population model to estimate instar-specific vital rates in the bean weevil, Callosobruchus maculatus across a food quality gradient. We characterize food quality effects on the bean weevil's life history traits throughout its juvenile ontogeny to test how food quality impacts instar-specific vital rates.3. Vital rates differed across food quality treatments within each instar; however, their effect differed with instar. Weevils consuming low-quality food spent 38%, 37%, and 18% more time, and were 34%, 53%, and 63% smaller than weevils consuming high-quality food in the second, third, and fourth instars, respectively.Overall, our results show that consuming poor food quality means slower growth, but that food quality effects on vital rates, growth and development are not equal across instars. Differences in life history traits over juvenile ontogeny in response to food quality may impact how organisms interact with their environment, including how susceptible they are to predation, parasitism, and their competitive ability. K E Y W O R D Scowpea weevil, juvenile ontogeny, phytophagous consumer, stage-structured population model | 627 HOLMES Et aL.

No life‐history cost of tebufenozide resistance in the smaller tea tortrix moth

Lee

Smith

Pest Management Science

et al. 2023

BACKGROUND: Tebufenozide is widely used to control populations of the smaller tea tortrix, Adoxophyes honmai. However, A. honmai has evolved resistance such that straightforward pesticide application is an untenable long-term approach for population control. Evaluating the fitness cost of resistance is key to devising a management strategy that slows the evolution of resistance.RESULTS: We used three approaches to assess the life-history cost of tebufenozide resistance with two strains of A. honmai: a tebufenozide-resistant strain recently collected from the field in Japan and a susceptible strain that has been maintained in the laboratory for decades. First, we found that the resistant strain with standing genetic variation did not decline in resistance in the absence of insecticide over four generations. Second, we found that genetic lines that spanned a range of resistance profiles did not show a negative correlation between their LD 50 , the dosage at which 50 % of individuals died, and life-history traits that are correlates of fitness. Third, we found that the resistant strain did not manifest life-history costs under food limitation. Our crossing experiments indicate that the allele at an ecdysone receptor locus known to confer resistance explained much of the variance in resistance profiles across genetic lines. CONCLUSION: Our results indicate that the point mutation in the ecdysone receptor, which is widespread in tea plantations in Japan, does not carry a fitness cost in the tested laboratory conditions. The absence of a cost of resistance and the mode of inheritance have implications for which strategies may be effective in future resistance management efforts.