Abstract
Two broad classes of arthropod natural enemies attack insect herbivores: specialists and generalists. The tight dynamical linkage of specialist natural enemies and their prey may make the specialists able to respond numerically to, and perhaps suppress, herbivore outbreaks. Because generalist predators may attack not only herbivores, but also the herbivores' specialist natural enemies, generalist predators may disrupt control of herbivore populations rather than contribute to it. We examined interactions between pea aphids (Acyrthosiphon pisum), a specialist parasitoid wasp (Aphidius ervi) that attacks the aphids, and a common generalist predator, carabid beetles (primarily Pterostichus melanarius). In two field experiments in alfalfa, we manipulated carabid densities to measure their direct (through predation) and indirect (through intraguild predation on A. ervi) impact on aphid population dynamics. The first experiment was initiated when plants were short (following cutting), and carabid predation of aphids led to an immediate reduction in aphid densities. This reduction was short-lived, however, because carabids reduced parasitism, leading to higher aphid population growth rates. Therefore, although the immediate direct effect of carabids was a reduction in aphid densities, this was offset in the longer term by the indirect effect of carabids disrupting the control of aphids by parasitoids. The second experiment was initiated after plants had regrown following cutting. When plants were tall, carabids had no direct impact on aphid densities. Nonetheless, the slow indirect effect of carabids on aphid densities through reduction in parasitism still occurred, leading to higher aphid population growth rates in the presence of carabids. Additional laboratory experiments demonstrated that carabids are able to climb into plants and prey upon the immobile parasitoid pupae (“mummies”), whereas antipredator behaviors of the aphids protect them from predation by carabids when plants are tall. Overall, carabid predation caused an immediate but ephemeral decrease in aphid density. In contrast, the indirect positive effect on aphid density caused by reducing parasitism developed later but persisted longer. Thus the generalist carabid primarily acted as an intraguild predator, interrupting aphid population control by the specialist parasitoid.
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Claims 8
Claim · model-written summary
Carabid predation immediately reduced aphid density in short alfalfa.
- Taxon
- alfalfa
Medicago sativat0 - Treatment
- carabid predatione0
- Interactor
- aphidsAphidomorphae0pest
- Second interactor
- carabide0biocontrol_agent
- Outcome
- aphid densitiese0
- Direction
- reductione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“carabid predation of aphids led to an immediate reduction in aphid densities”
t0“field experiments in alfalfa”
Claim · model-written summary
Carabids reduced aphid parasitism.
- Taxon
- alfalfaMedicago sativat0
- Treatment
- carabidse0
- Interactor
- aphide0pest
- Second interactor
- carabidse0biocontrol_agent
- Outcome
- parasitisme0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“carabids reduced parasitism, leading to higher aphid population growth rates”
t0“field experiments in alfalfa”
Claim · model-written summary
Carabid presence increased aphid population growth rates.
- Taxon
- alfalfaMedicago sativat0
- Treatment
- carabidse0
- Interactor
- aphide0pest
- Second interactor
- carabidse0biocontrol_agent
- Outcome
- aphid population growth ratese0
- Direction
- highere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“carabids reduced parasitism, leading to higher aphid population growth rates”
t0“field experiments in alfalfa”
Claim · model-written summary
In tall alfalfa, carabids had no direct impact on aphid density.
- Taxon
- alfalfaMedicago sativat0
- Treatment
- carabidse0
- Interactor
- aphide0pest
- Second interactor
- carabidse0biocontrol_agent
- Outcome
- aphid densitiese0
- Direction
- no direct impacte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When plants were tall, carabids had no direct impact on aphid densities”
t0“field experiments in alfalfa”
Claim · model-written summary
Carabids climbed plants and preyed on parasitoid pupae.
- Taxon
- alfalfaMedicago sativat0
- Interactor
- parasitoide0biocontrol_agent
- Second interactor
- carabidse0biocontrol_agent
- Outcome
- prey upon the immobile parasitoid pupaee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“carabids are able to climb into plants and prey upon the immobile parasitoid pupae (“mummies”)”
t0“field experiments in alfalfa”
Claim · model-written summary
Aphid antipredator behavior protected them from carabids in tall plants.
- Taxon
- alfalfaMedicago sativat0
- Interactor
- aphidsAphidomorphae0pest
- Second interactor
- carabidse0biocontrol_agent
- Outcome
- protect them from predation by carabidse0
- Qualifier
- when plants are talle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“antipredator behaviors of the aphids protect them from predation by carabids when plants are tall”
t0“field experiments in alfalfa”
Claim · model-written summary
The direct decrease in aphid density was short lived.
- Taxon
- alfalfaMedicago sativat0
- Interactor
- aphide0pest
- Second interactor
- carabide0biocontrol_agent
- Outcome
- aphid densitye0
- Direction
- decreasee0
- Qualifier
- immediate but ephemerale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“carabid predation caused an immediate but ephemeral decrease in aphid density”
t0“field experiments in alfalfa”
Claim · model-written summary
The indirect increase in aphid density persisted longer.
- Taxon
- alfalfaMedicago sativat0
- Interactor
- aphide0pest
- Outcome
- aphid densitye0
- Direction
- positive effecte0
- Qualifier
- developed later but persisted longere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the indirect positive effect on aphid density caused by reducing parasitism developed later but persisted longer”
t0“field experiments in alfalfa”