Higher parasitic load was detected in the spiders in
ginger
Entomopathogenic fungus and hymenopteran taxa were detected in spiders
collected from both ginger and native forest (Figure 8). While these
reads likely originate from parasitized prey rather than parasitized
spiders, the high incidence of parasitism within arthropod taxa across
both ginger and native forest, but especially in ginger, is apparent.
This is yet another benefit of high throughput sequencing approaches;
not only can prey communities be detected, but parasites of prey
themselves may be detected, supported in other studies (Traugott &
Symondson 2008).
We can identify some well-known lepidopteran parasitoids that have been
accidentally or purposefully introduced, including Cotesia
vestalis , Ichneumon xanthorius , Meteorus laphygmae , and
the scale parasite Aphytis chrysomphali ; these parasitoids are
found in both native forest and ginger-invaded sites. The major
hymenopteran parasitoids were braconids, in particularMicroctonus (Rhopalophorus ) which is a well-known
adventive species across the islands (Nishida 2002) and appears to
parasitize beetles, notably chrysomelids (Beardsley 1961). Infiltration
of native forest by nonnative parasitoids, in particular parasitoids of
Lepidoptera, has been well documented (Henneman & Memmott 2001). Their
prevalence in spiders from native forest, then, is not surprising.
However, we do show that the overall prevalence of Hymenoptera was
higher in ginger-invaded sites than native sites. A wasp, in the
non-native family Pteromalidae (Beardsley 1961; Nishida 2002) was found
exclusively on ginger; Pteromalidae are mostly parasitoids of
Lepidoptera and Coleoptera, but can also attack larvae and pupae of
Diptera and the eggs of Coccidae. Spiders from the ginger-invaded sites
also showed a higher diversity of other parasitoids, includingOrasema sp., in which the one species known from Hawaii is a
parasite of another invasive species in Hawaii, the little fire ant
(Heraty et al. 2021).
Entomopathogenic fungal reads were detected predominantly using 28s;
while not the most widely used marker for fungal DBA barcoding, 28s has
been shown to be relatively effective (Xu 2016; Zhao et al.2011). For the sequences detected in the spiders in our study, their
high percent identity matches and known presence on Hawaii provides more
support for our finding. Entomopathogenic fungi were detected in 22
spiders in ginger sites while only found in 1 spider from native forest.
This result is consistent with previous work in New Zealand which has
shown that fungivores are much more abundant in sites that have been
invaded by ginger (Bassett 2014). The entomopathogenic fungiGibellula, the most common spider fungal pathogen (Shresthaet al. 2019), was detected in only one spider in native forest.Beauveria was the most commonly detected fungi in spiders from
ginger-invaded sites, followed by Ophiocordyceps , a known
parasite of beetle larvae (Wang et al. 2021). Beauveria is genus
of cosmopolitan fungal pathogens, found associated with arthropods and
the surrounding habitat, including in the soil and on vegetation. It has
a wide host range over 17 arthropod orders which includes spiders
(Shrestha et al. 2019; Zimmermann 2007), although infections have
been seldomly documented (Meyling & Eilenberg 2007). In Hawai‘i,B. bassiana is used as a component of integrated pest management
strategies in coffee plantations to control the coffee berry borer
(Hypothenemus hampei ) first detected in Hawai‘i in 2014 (Grecoet al. 2018; Hollingsworth et al. 2020). Multiple
indigenous strains of B. bassiana are now found in Hawai‘i and
detected in crops where there were no previous mycoinsecticide treatment
(Castrillo et al. 2020; Hollingsworth et al. 2011).
While we cannot comment on the particular strain or on the arthropod
host with which Beauveria was carried, its prevalence, along with
presence of other parasites, demonstrates a higher parasitic load
found in the arthropods from ginger sites. Because entomopathogenic
strains such as Beauveria and Ophiocordyceps are known to
infect spiders, interaction with infected prey may then increase the
risk of infection of the spider itself, unlike prey infected by
hymenopteran parasitoids. Additionally, parasitism can impart indirect
effects by altering prey density or prey behavior. The higher detection
of parasites, then, supports that ginger-invaded habitat may produce
suboptimal habitat for native arthropods by introducing new biotic
interactions with potentially harmful taxa.