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

Published May 08, 2025 on Dryad. https://doi.org/10.5061/dryad.41ns1rnr4

Data files

May 08, 2025 version files 3.24 KB

Predator_experiment.txt

1.37 KB
README.md

1.87 KB

Abstract

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.

https://doi.org/10.5061/dryad.41ns1rnr4

Description of the data and file structure

An experiment testing the hypothesis that fecal strings placed by females on insect eggs provide protection against predation. The study was motivated by the observation that some species in Galerucella (Coleoptera: Chrysomelidae) place a fecal strings whereas others do not, but also that eggs in these species are often aggregated. The aim was to evaluate whether the efficiency of the fecal strings also depended on the egg number.

Setup: Each trial include an egg batch (2, 4, 8, 12, 16, 20 or 24 eggs) of three types: (a) Eggs of G. lineola that naturally have fecal strings, (b) Eggs of G. lineola that were cleaned and where fecal strings were removed and (c) Eggs of G. sagittariae that naturally lack fecal strings.

Files and variables

File: Predator_experiment.txt

Description:

Variables

Species: Gl = Galerucella lineola, Gs = Galerucella saggitariae
Treatment: Control = natural; Clean = cleaned eggs (only Gl)
Egg_dens: The number of initial eggs in the petri dish
Consumed: The number of eggs consumed by the predator (Paederus riparius)
Survived: The number of surviving eggs
Prop_cons: The proportion consumed

Code/software

Analyses were run in R, with glmer in the lme4 package:

glmer(Survival~Egg\_density*Treatment+(1|Batch),data

For this analysis, the data was reformated so that each row was a single egg that survived or was consumed (0/1-variable) and where batch is the trial in the same petri dish. This test models whether the probability of egg survival depends on if the egg has a fecal string, on the number of eggs in the batch, and on the combination of these two.