4 research outputs found
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Consequences of host quality variation for the behaviour, life histories and ecological interactions of insects at higher trophic levels
Species interactions have caught ecologists’ attention since the field of ecology first
developed. Direct effects between species are readily recognised as the interaction is explicit
and easy to detect. In contrast, indirect effects are masked under direct effects and difficult
to detect. However, ecologists have been attempting to quantify and understand the role of
indirect effects on community structure. In Chapter 1, I reviewed the literature, clarifying the
basic definitions of direct and indirect effects, and then apply these concepts to components
in my study systems. I employed two different study systems to examine direct (host seed�bean beetle system) and indirect (plant pathogen-plant-insect system) effects in this thesis.
In Chapter 2, I explored the direct effects of host quality and maternal effects on preference
and performance of two bean beetle species, Callosobruchus maculatus and C. analis. They
showed similar and consistent preference, but their performance was species dependent and
influenced by both host and maternal effects. In Chapter 3, I investigated the direct effects
of host quality and mating status on C. maculatus reproductive costs. I found that host quality
affects beetle longevity, and this effect also depends on mating status, which then differs
between treatments and sexes. In Chapter 4, I examined the indirect effects emanating from
the plant pathogen Botrytis cinerea on two aphid species, Aphis fabae and Acyrthosiphon
pisum. I found that A. fabae experiences indirect negative effects while Ac. pisum gains
indirect positive effects from B. cinerea infection. In Chapter 5, I investigated the indirect
effects of B. cinerea infection on A. fabae and their natural enemies and ant mutualists in the
field, where levels of urbanisation varied. My results suggest that the population of A. fabae
is influenced by infection, while the population of aphid natural enemies and ant mutualists
are instead dependent on urbanisation. In Chapter 6, I investigated the effects of plant
pathogens on insect herbivores’ natural enemies using meta-analysis technique. I found no
overall effects of plant pathogens on insect natural enemies, but if considered by type of
pathogen, I found fungal pathogens cause consistent indirect negative effects, while bacterial
pathogens show indirect positive effects on insect natural enemies. No significant effects of
viral pathogens were found. In my last Chapter (Chapter 7), I discuss the main findings,
contributions and further recommendations of my study
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Aphids show interspecific and intraspecific variation in life history responses to host plant infection by the fungal pathogen Botrytis cinerea
The life histories of insect herbivores are affected by variation in host plant quality, with poor quality typically being associated with reduced herbivore fecundity, size and longevity. Plant pathogens are ubiquitous in nature and can alter host plant quality as experienced by insect herbivores. We asked how host plant infection by the widespread and economically important fungal pathogen Botrytis cinerea affected the life history traits of two aphid species. We found that the life history traits of the black bean aphid Aphis fabae were negatively affected by being reared on infected host plants, showing reduced fecundity, population growth rate, size, off-plant survival time and development rate. In contrast, we found that pea aphids Acyrthosiphon pisum benetted from being reared on infected plants, and that the degree of benet varied between pea aphid clonal lines. This work suggests that the ecological and economic consequences of plant pathogen infection on the dynamics of aphid pests could be difcult to predict
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Urbanization and plant pathogen infection interact to affect the outcome of ecological interactions in an experimental multitrophic system
Urbanization can change interactions in insect communities, and the few studies of tritrophic interactions in urban settings focus on interactions between plants, herbivorous insects and their mutualists and natural enemies. Plant pathogen infection is also widespread and common, and infection may also alter such interactions, but we have no understanding of whether the ecological consequences of pathogen infection vary with urbanization. Using replicated aphid colonies on experimental plants, we investigated how infection by the plant pathogen Botrytis cinerea influences interactions between plants, aphids and the aphid natural enemies and ant mutualists in highly urbanized, suburban and rural study sites. Aphid and natural enemy abundance were highest in the suburban site, while mutualist ants were most abundant in the urban site, reversing the usual positive density-dependent relationship between natural enemies and aphids. The effect of pathogen infection varied with trait and site, mediated by natural enemy preference for hosts or prey on uninfected plants. The effect of infection on aphid abundance was only seen in the suburban site, where natural enemies were most abundant on uninfected plants and aphid numbers were greatest on infected plants. In the urban site, there was no effect of infection, while in the rural site, aphid numbers were lower on infected plants. Uninfected plants were smaller than infected plants and differed between locations. This study suggests that the effects of urbanization on ecological interactions may become more complex and difficult to predict as we study ecological assemblages and communities at greater levels of structural
complexity
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Differing effects of parental and natal hosts on the preference and performance of the stored product pests Callosobruchus maculatus and C. analis
Bean beetles (Bruchinae) are a taxon of seed predators and several species are economically significant stored product pests. Seed quality may affect adult life history traits, with consequences for their population dynamics. We investigated if variation in host quality (poor quality: lentil; high quality: mung bean) as experienced by the parental (i.e. the individuals ovipositing) generation and the natal (i.e. the study individuals emerging from the host) generation influenced the preference and performance of Callosobruchus maculatus and C. analis. Both species preferred ovipositing on mung bean regardless of experience. Emergence rate was high for all treatments except for C. maculatus reared on mung, whose offspring did poorly when developing in lentil. The sex ratio of emerging offspring was 1:1 except for C. analis emerging from lentil, which was female biased if the parents were reared on lentil, but male biased if reared on mung. In C. analis, lentil parental host resulted in larger offspring irrespective of natal host, while in C. maculatus larger offspring emerged from mung as natal host. Overall, males emerging from lentils obtained more matings, except with C. maculatus where females had emerged from mung, where there was no preference. Development time for beetles was increased for those with parents reared on mung and for those with lentil natal hosts. For C. analis there was no difference in survival time for those where the parental host was lentil, but when the parental host was mung, then there was a significant reduction in survival time for those whose natal host was also mung, compared to those emerging from lentils. This work shows that predicting the effect of host quality on traits requires more than single-species, single-generation studies, as transgenerational effects can influence the performance and preference of closely related stored product pest species in quite different ways