Intro
The mechanism explained as a previously proposed explanation of how members of a given group benefit from a reduction in parasitism and predation rates and how it happens
dilution effect -- occurs when predator attacks do not increase in the same proportion as group size does
The species studied, Ascia monuste orseis, is commonly found in this region.
Neotropical region
What tests were run?
data on number of larvae recorded in each treatment were analyzed with respect to normality (Shapiro-Wilk tests)
homoscedasticity of variances (Bartlett tests)
Tukey contrast tests were run for paired comparisons between treatments
For each treatment, the relative risk of at- tacks by the main natural enemies (parasitoid wasps, predato- ry wasps, ants, and spiders; see results) was compared within both early and late instars using a chi-square test
Two types of cues used by natural enemies to locate larvae
visual and chemical cues
What cues do natural predators use to find their prey
prey morphology, chemistry, and behavior.
Larval groups of these sizes were observed to study aggregation effects
1, 10, and 50 larvae
Early instars were more susceptible to attacks by these types of predetors
ants and spiders
Larval vulnerability of A. monuste orseis to natural enemies was affected by
Group size and larval age
Compare and contrast the pros and cons of gregariousness
Pros -- higher survivorship, growth rates, and feeding facilitation
Cons -- increased risk of infectious diseases, intraspecific competition for food, and conspicuousness to natural enemies
The frequency of these events was recorded during observations of larval behaviors.
attack frequency of natural enemies on different treatments throughout larval development
What the larvae spent the most time doing
In general, larvae spent half of the observation time resting (50%) and the other half feeding (25%), searching (20%), or moving (5%) (Fig. 2)
The researchers propose this area of research for future studies on larval defense strategies
the role of visual and chemical cues in enemy attraction
Other aspects that needed to be explored further
Escape and defense behaviors, risky behaviors of gregarious insects,
How they controlled for the effects of larval manipulation on group behavior
during group formation, all the larvae were gently manipulated with a thin brush.
Despite more attacks occurring on larger groups, this risk metric was lower for individuals
per capita attack risk
This behavior posed more predation risks to larvae of A. monuste orseis
behaviors that involved head movements such as searching and feeding posed more predation risks to larvae of A. monuste orseis than resting and moving, even though the former consumes about half of the time spent by larvae.
We hypothesized that larval aggregation in A. monuste orseis decreases the per capita risk of mortality from natural enemies, thus increasing the individual’s chances of survival as the group size increases. We also predicted that group behaviors that include head movements such as feeding and searching are more risky than resting or walking.
How attacks were defined
Each attack was defined as insertion of the ovipositor into the larva’s body (for parasitoids) and as removal of larvae from the aggregation (for predators) by using mandibles or legs.
what occured to repel parasitoids when a larvae was approached by one
When a parasitoid approached the larvae, on a few occasions, the group responded to its presence by remaining motionless. When a larva was attacked, it moved its head in rapid ventro-dorsal movements (headrearing). After a larva displayed this behavior, the other larvae reacted similarly. This collective behavior was effective in repelling the parasitoids in two occasions (Table 2).
Why larger larval groups were more at risk when feeding and searching, regardless of larval size
Signal amplification