Baronia brevicornis caterpillars build shelters to avoid predation

Vertical stratification and defensive traits of caterpillars against parasitoids in a lowland tropical forest in Cameroon

Insect herbivores and their parasitoids play a crucial role in terrestrial trophic interactions in tropical forests. These interactions occur across the entire vertical gradient of the forest. This study compares how caterpillar communities, and their parasitism rates, vary across vertical strata and between caterpillar defensive strategies in a semi deciduous tropical forest in Nditam, Cameroon. Within a 0.1 ha plot, all trees with a diameter at breast height (DBH) ≥ 5 cm were felled and systematically searched for caterpillars. We divided the entire vertical gradient of the forest into eight, five-metre strata. All caterpillars were assigned to a stratum based on their collection height, reared, identified, and classified into one of three defensive traits: aposematic, cryptic and shelter-building. Caterpillar species richness and diversity showed a midstory peak, whereas density followed the opposite pattern, decreasing in the midstory and then increasing towards the highest strata. This trend was driven by some highly dense shelter-building caterpillars in the upper canopy. Specialisation indices indicated decreasing levels of caterpillar generality with increasing height, a midstory peak in vulnerability, and increasing connectance towards the upper canopy, although the latter was likely driven by decreasing network size. Both aposematic and shelter-building caterpillars had significantly higher parasitism rates than cryptic caterpillars. Our results highlight nuanced changes in caterpillar communities across forest strata and provide evidence that defences strategies are important indicators of parasitism rates in caterpillars and that both aposematic and shelter-building caterpillars could be considered a "safe haven" for parasitoids.

Experimental shelter-switching shows shelter type alters predation on caterpillars (Hesperiidae)

Caterpillars build various shelters that protect them from natural enemies, but whether specific shelters provide different protection is unknown. To disentangle a caterpillar species’ shelter from the rest of its phenotype, we performed a field experiment in which two caterpillar species (Urbanus dorantes and U. proteus) were removed from their original shelters, placed into shelters made by conspecifics or heterospecifics, and monitored for predation and parasitism. Predation was intense, with 0–48% of caterpillars surviving depending on treatment. Shelter builder identity significantly affected predation independent of occupant identity, with caterpillars placed in U. proteus shelters experiencing higher predation than those in U. dorantes shelters. The effect of shelter builder identity was related to shelter type: shriveled leaf shelters built by U. dorantes had a lower risk of predation than cut-and-fold shelters built by either species. Cut-and-fold shelters built by the two species did not have significantly different shapes. Caterpillar stage also significantly affected predation (mid-instars were more successful than early instars), but caterpillar species identity did not. Surprisingly, parasitism was rare, but both shriveled leaf shelters and cut-and-fold shelters resulted in similar overall caterpillar mortality. The differences in predation and overall mortality between shelter types suggest a trade-off between protection from predators and parasitoids. This experiment demonstrates that shelter type determines the fate of the caterpillar inside, independent of the identity of the caterpillar that built the shelter. This is the first experimental evidence that predation may select for shelter type and associated shelter-building behavior in Lepidoptera.