Elevational contrast in predation and parasitism risk to caterpillars in a tropical rainforest

Abstract

Invertebrate predators and parasitoids are among the most important natural enemies of insect herbivores. Yet, the strength of natural enemy pressure along an altitudinal gradient and interactions between the groups of natural enemies (such as predation on parasitized prey) are not well known. Various methods are used to reveal the mortality factors of herbivores. Predation pressure is usually assessed through exposure of artificial prey. However, this method cannot provide information about the attacks of parasitoids, or their eventual interactions with predators. Furthermore, artificial or dead prey might not attract predators because they do not show expected host behavior, and this method mostly cannot distinguish between predation and scavenging. For the first time in a tropical rainforest, we quantified elevational contrast in mortality factors using exposure of live caterpillars. We exposed a total of 800 live caterpillars of Talanga excelsalis moresbyensis Strand (Lepidoptera: Crambidae) on saplings of Ficus copiosa Steud. (Moraceae) at two elevations in primary tropical rain forest in Papua New Guinea (200 and 1 200 m a.s.l.). We exposed the caterpillars in two treatments: exposed to and protected from invertebrate predators and parasitoids. Disappearance of caterpillars was significantly higher in the exposed treatment. Furthermore, caterpillar disappearance was significantly higher in lowlands than in highlands (43 vs. 12%). We consider the vast majority of the disappearance to be due to predation, as migration of the caterpillars from the focal trees was not observed (except one caterpillar). This estimate of invertebrate predation rate corresponds with studies which used artificial caterpillar models. No significant difference in parasitism rate between the two elevations was observed (12 vs. 13%). The combination of the disappearance and parasitism rate patterns means that larval parasitoids face stronger pressure from invertebrate predators through higher predation of their hosts in the lowlands than in the highlands.

Between predators and parasitoids: Complex interactions among shelter traits, predation and parasitism in a shelter‐building caterpillar community

“…Most of this uncertainty concerns the fates of the caterpillars that disappeared. The available literature (Libra, Tulai, Novotny, & Hrcek, 2019; Loeffler, 1996) and all our observations indicate that shelter‐building caterpillars are quite sedentary. We saw many free‐feeding caterpillars hanging from silk lines or travelling rapidly over bare earth or branches, but we never saw shelter‐building species outside their shelters unless they were feeding or building.…”

Predation and parasitism on herbivorous insects change in opposite directions in a latitudinal gradient crossing a boreal forest zone

“…This may be especially true for endoparasitoids of endophagous leafminers (Péré et al, 2013). The frequent occurrence of reciprocal patterns between predation and parasitism in between-site comparisons (Cornelisson & Stiling, 2009;Hawkins et al, 1997;Libra et al, 2019) may result from the increase in parasitoid mortality with an increase in predation on parasitised hosts (Libra et al, 2019). Thus, herbivorous insects often escape one type of enemy only to succumb to another (Hawkins et al, 1997).…”

Molecular analyses reveal consistent food web structure with elevation in rainforestDrosophila- parasitoid communities

“…Temperature changes rapidly with elevation, so transects spanning elevations on mountain slopes can approximate aspects of climate change, while avoiding many of the confounding factors that complicate analyses of latitudinal gradients (Hodkinson 2005, Körner 2007, Malhi et al 2010, Morris et al 2015. There is an expectation that predation and parasitism risk increase with temperature (Roslin et al 2017, Libra et al 2019, but it is unclear how such changes are expressed at the community level. Quantitative food webs should be particularly valuable in exploring changes in species interactions with changes in temperature, because they incorporate the relative abundances and interaction frequencies of component species (Memmott and Godfray 1994).…”