Competitor‐free space mediates non‐target impact of an introduced biological control agent

Abstract

1. Enemy-free space has been shown to mediate host shifts in herbivores, but this has not previously been documented in parasitoids. Also, natural enemies shown to maintain host shifts have always been from higher trophic levels, rather than competitors.2. In Hawaii, an Australian parasitoid ( Diachasmimorpha tryoni ) of medflies that loses competition contests to a subsequently introduced Asian parasitoid ( Fopius arisanus ) has shifted its realised host range to attack non-target gall flies on lantana.3. The present study demonstrates experimentally that D. tryoni reproduction is: (i) lower on medflies in coffee when F. arisanus is present than when it is absent; (ii) higher in gall flies on lantana than on medflies in coffee, when F. arisanus is present; and (iii) higher in medflies on coffee than in gall flies on lantana, when F. arisanus is absent. This meets Berdegue et al. 's ( Ecological Entomology , 21 , 203 -217, 1996) three conditions to confirm the importance of enemy-free space.4. In the field, F. arisanus is abundant on medflies, whereas D. tryoni is rare on medflies, but is the dominant parasitoid of lantana gall flies.5. Competitor-free space is thus shown to be a key mechanism maintaining an apparent host shift by an introduced biocontrol agent onto a non-target species.

Food plant and herbivore host species affect the outcome of intrinsic competition among parasitoid larvae

“…Moreover, in diverse or structurally complex habitats, intrinsically inferior species may find complementary niches that reduce or even eliminate competition. For example, inferior competitors may have longer ovipositors and can exploit hosts that hide deeper in fruits, galls or leaves (Paranhos et al, 2013) or may reproduce at a faster rate than superior competitors on some resources (Messing & Wang, 2009).…”

The Roles of Parasitoid Foraging for Hosts, Food and Mates in the Augmentative Control of Tephritidae

“…(8) Not only is it important that a parasitoid attacks the target pest but also that it does not attack non-targets which can include rare non-pestiferous congeners or even seed-head attacking tephritids that were themselves introduced for the biological control of weeds. This can be a challenge since the natural history and even the hosts of many Tephritidae are unknown and parasitoid host preferences can change rapidly when confronted with new environments and competitors [ 86 , 87 ]. Another form of “non-target” at risk is the pre-existing and locally-adapted populations of the parasitoid being mass-reared and released.…”

Using evolutionary tools to facilitate the prediction and prevention of host‐based differentiation in biological control: a review and perspective

“…). Messing & Wang () suggest that the parasitoids made the shift as the new host offered a competitor‐free space, similar conceptually to enemy‐free space. This is especially interesting given that it has adapted to substantially different host biology (fly larvae gall versus in soft fruits) possibly to avoid this competition.…”