Host size and spatiotemporal patterns mediate the coexistence of specialist parasitoids

Abstract

Abstract.Many insect parasitoids are highly specialized and thus develop on only one or a few related host species, yet some hosts are attacked by many different parasitoid species in nature. For this reason, they have been often used to examine the consequences of competitive interactions. Hosts represent limited resources for larval parasitoid development and thus one competitor usually excludes all others. Although parasitoid competition has been debated and studied over the past several decades, understanding the factors that allow for coexistence among species sharing the same host in the field remains elusive. Parasitoids may be able to coexist on the same host species if they partition host resources according to size, age, or stage, or if their dynamics vary at spatial and temporal scales. One area that has thus far received little experimental attention is if competition can alter host usage strategies in parasitoids that in the absence of competitors attack hosts of the same size in the field. Here, we test this hypothesis with two parasitoid species in the genus Aphytis, both of which are specialized on the citrus pest California red scale Aonidiella aurantii. These parasitoids prefer large scales as hosts and yet coexist in sympatry in eastern parts of Spain. Parasitoids and hosts were sampled in 12 replicated orange groves. When host exploitation by the stronger competitor, A. melinus, was high the poorer competitor, A. chrysomphali, changed its foraging strategy to prefer alternative plant substrates where it parasitized hosts of smaller size. Consequently, the inferior parasitoid species shifted both its habitat and host size as a result of competition. Our results suggest that density-dependent size-mediated asymmetric competition is the likely mechanism allowing for the coexistence of these two species, and that the use of suboptimal (small) hosts can be advantageous under conditions imposed by competition where survival in higher quality larger hosts may be greatly reduced.

Overstinging by hymenopteran parasitoids causes mutilation and surplus killing of hosts

“…chrysomphali and, moreover, reduced the fecundity of the surviving females, which demonstrates the superiority of A. melinus as a biological control agent of A. aurantii compared with A. chrysomphali (DeBach and Sisojevic 1960;Rosen and DeBach 1979;Pekas et al 2010Pekas et al , 2016Boyero et al 2014;Cebolla et al 2017). The mortality caused by A. melinus was fourfold greater than that caused by A. chrysomphali when considering the three behaviors measured in this assay (parasitism, host-feeding and overstinging).…”

Intraspecific interference between native parasitoids modified by a non‐native parasitoid and its consequence on population dynamics

“…In contrast to the well‐studied food webs consisting of two competitors attacked by a single predator or parasitoid (e.g. Bonsall & Hassell, 1997; Ohgushi, 2005; Tack et al ., 2011), mechanisms for the variety of population dynamics in food webs with two co‐occurring parasitoid (or predator) species competing for single host (or prey) species are less understood (Matsumoto et al ., 2003; Borer et al ., 2004; Bader et al ., 2006; Boivin & Brodeur, 2006; Tuda et al ., 2006; Peri et al ., 2014; Pekas et al ., 2016). In this respect, our results provide empirical evidence bridging top‐down and bottom‐up approaches to describe one host–two parasitoid food web dynamics.…”

Coexistence of two termite‐eating specialists (Araneae)

“…predators with narrow trophic breadths, possess specialised adaptations that enhance exploitation of the selected prey, but often restrict exploitation of an alternative host/prey (Pekár & Toft, 2015), so the trophic niche differentiation is limited. Evidence suggests that specialists can be separated temporally and spatially (Inbar & Wool, 1995), or by exploiting the same prey but of different sizes (Pekas et al ., 2016), genotype (Smith et al ., 2008) or stage (Wu et al ., 2019). Thus, the coexistence of specialists can be explained by similar mechanisms as between generalists, namely niche partitioning (Hardin, 1960).…”