Deterring egg predators with fecal strings is more efficient when eggs are aggregated

Predation on insect eggs can be very high and female insects use multiple
antipredator strategies to reduce egg mortality. Two common strategies are
to aggregate eggs, that may function to satiate egg predators, and various
deterrence strategies, such as the addition of fecal strings on top of the
egg. We tested the hypothesis that these two strategies work best in
combination, where egg aggregation may strengthen the effect of deterrence
strategies. We compared egg predation by the predator Paederus riparius
both within species Galerucella lineola (cleaned eggs versus egg with
fecal strings), and between the species G. lineola and G. sagittariae
(where the latter species naturally lack fecal strings). Our findings
revealed a robust treatment interaction, where fecal strings and egg
density affected egg survival when exposed to Paederus riparius. Egg
survival increased with egg density for eggs with fecal strings but was
constantly low on eggs without fecal strings (cleaned G. lineola eggs or
G. sagittariae eggs). This study emphasized the need of a combine of
insect defensive measures to prevent herbivorous insect interactions with
their natural predators.