developmental growth strategies (Firlej et al. 2007), increasing host suitability in the
future. The fact that D. coccinellae has been consistently detected on this invasive
species suggests that it may benefit from a marginal host, when for example, native
species fluctuate in numbers.
Invasive insect species are often pests of agricultural plants and plantation trees,
and in South Africa, alien biological control agents (including parasitic wasps) have
been introduced to regulate them or have been accidentally co-introduced (e.g. in
Eucalyptus plantations: Wingfield et al. 2008; Garnas et al. 2012; Bush et al. 2016).
These species are also often reported to harbour a high diversity of natural enemies.
For example, 22 species of parasitoids and hyperparasitoids emerged from Diamondback Moth (Plutella xylostella, a notorious pest of cultivated and native
brassicas in the region) larvae and pupae sampled in South Africa (Kfir 1998). A
few of the parasitoids had restricted distributions in South Africa and, together with
their degree of host-specificity, suggests that host and parasite had time to co-evolve
(Kfir 1998). Similarly, P. xylostella monitored on canola revealed novel associations
with a large diversity of native larval and pupal parasitoids, infecting the host
distinctively in terms of extent and timing of parasitism (Mosiane et al. 2003).
Hyperparasitoids were also found to feed on the cocoons of primary parasitoid
larvae and were influenced by the abundance and timing of the latter (Mosiane
et al. 2003; Nofemela and Kfir 2005). Therefore, the complexity of these tri-trophic
relationships, including potential density-dependent and cascading top-down effects,
are likely to modulate the dynamics of these pests and invasive populations
(Nofemela 2013).
Besides direct effects across trophic levels as discussed above, there are also
examples of indirect effects in biotic interactions that affect the invasive host or,
alternatively, an invasive species can also be a key player in the regulation of hostparasite interactions. For example, inter-specific competition between native and
invasive ant species, including the Argentine Ant (Linepithema humile), can disrupt
associations between parasitoids and hemipteran pests that produce honeydew
sought by the ants (Mgocheki and Addison 2010). Argentine Ant invasions may
also disrupt native plant-ant interactions, such as myrmecochorous seed dispersal, as
has been found in many parts of the world where this invasive ant is present
(reviewed in Traveset and Richardson 2014; see also Janion-Scheepers and Griffiths
2020, Chap. 7, Box 7.6).
Lastly, insect biotic interactions include non-target associations of insect herbivores introduced as biological control agents of invasive plants. In this case, the alien
herbivore is attacked by native parasitoids, potentially reducing the level of biological control achieved on the target alien plant. For example, the bud-galling wasp,
Trichilogaster acaciaelongifoliae, introduced in 1982 to South Africa from
Australia to control Acacia longifolia quickly acquired novel communities of natural
parasitoids (Manongi and Hoffmann 1995; McGeoch and Wossler 2000; Veldtman
et al. 2011). Veldtman et al. (2011) showed that 33% of novel natural enemies found
in the introduced range belong to the same families as its native enemies in Australia,
supporting parallels in food web dynamics between the two regions. Similarly,
several native parasitoids have been found to parasitise the larvae and pupae of the
14 Biotic Interactions as Mediators of Biological Invasions
403
future. The fact that D. coccinellae has been consistently detected on this invasive
species suggests that it may benefit from a marginal host, when for example, native
species fluctuate in numbers.
Invasive insect species are often pests of agricultural plants and plantation trees,
and in South Africa, alien biological control agents (including parasitic wasps) have
been introduced to regulate them or have been accidentally co-introduced (e.g. in
Eucalyptus plantations: Wingfield et al. 2008; Garnas et al. 2012; Bush et al. 2016).
These species are also often reported to harbour a high diversity of natural enemies.
For example, 22 species of parasitoids and hyperparasitoids emerged from Diamondback Moth (Plutella xylostella, a notorious pest of cultivated and native
brassicas in the region) larvae and pupae sampled in South Africa (Kfir 1998). A
few of the parasitoids had restricted distributions in South Africa and, together with
their degree of host-specificity, suggests that host and parasite had time to co-evolve
(Kfir 1998). Similarly, P. xylostella monitored on canola revealed novel associations
with a large diversity of native larval and pupal parasitoids, infecting the host
distinctively in terms of extent and timing of parasitism (Mosiane et al. 2003).
Hyperparasitoids were also found to feed on the cocoons of primary parasitoid
larvae and were influenced by the abundance and timing of the latter (Mosiane
et al. 2003; Nofemela and Kfir 2005). Therefore, the complexity of these tri-trophic
relationships, including potential density-dependent and cascading top-down effects,
are likely to modulate the dynamics of these pests and invasive populations
(Nofemela 2013).
Besides direct effects across trophic levels as discussed above, there are also
examples of indirect effects in biotic interactions that affect the invasive host or,
alternatively, an invasive species can also be a key player in the regulation of hostparasite interactions. For example, inter-specific competition between native and
invasive ant species, including the Argentine Ant (Linepithema humile), can disrupt
associations between parasitoids and hemipteran pests that produce honeydew
sought by the ants (Mgocheki and Addison 2010). Argentine Ant invasions may
also disrupt native plant-ant interactions, such as myrmecochorous seed dispersal, as
has been found in many parts of the world where this invasive ant is present
(reviewed in Traveset and Richardson 2014; see also Janion-Scheepers and Griffiths
2020, Chap. 7, Box 7.6).
Lastly, insect biotic interactions include non-target associations of insect herbivores introduced as biological control agents of invasive plants. In this case, the alien
herbivore is attacked by native parasitoids, potentially reducing the level of biological control achieved on the target alien plant. For example, the bud-galling wasp,
Trichilogaster acaciaelongifoliae, introduced in 1982 to South Africa from
Australia to control Acacia longifolia quickly acquired novel communities of natural
parasitoids (Manongi and Hoffmann 1995; McGeoch and Wossler 2000; Veldtman
et al. 2011). Veldtman et al. (2011) showed that 33% of novel natural enemies found
in the introduced range belong to the same families as its native enemies in Australia,
supporting parallels in food web dynamics between the two regions. Similarly,
several native parasitoids have been found to parasitise the larvae and pupae of the
14 Biotic Interactions as Mediators of Biological Invasions
403