Abstract
Entomophthoralean and ascomycetous fungi are the two major groups known to parasitize arthropods in almost every terrestrial habitat of the earth. Within Ascomycota, Cordyceps sensu lato is a large genus with more than 400 spp. described on numerous orders of Arthropoda. Among the hosts of Cordyceps, Coleoptera and Lepidoptera are the two major orders. Out of the estimated 200 Cordyceps spp. recorded on coleopteran and lepidopteran hosts, we have documented 92 spp. based on the available information of their host species. Among coleopteran hosts, Scarabaeidae and Elateridae are the two major families. Similarly, among lepidopterans, Hepialidae is the largest host family. Cordyceps militaris shows the widest host range, extending to 2 orders, 13 families, and 32 spp. We hope such accumulative work will be useful as a quick reference for interested biologists, forest ecologists, biocontrol researchers, and fungal and insect taxonomists to apprehend host range and host specificities of Cordyceps fungi.
1. Introduction
Fungi play vital roles in the recycling of organic matter in the terrestrial habitat of the earth. Besides that, they also parasitize living organisms and cause various diseases on plants, animals, and insects. Estimates show 750–1000 fungal spp. parasitizing insects naturally [1, 2], although the extent of the diversity of the entomopathogenic fungi is not completely known [3, 4]. The entomopathogenic fungi mainly belong to two diverse groups within kingdom Fungi, Entomophthorales (Phylum Entomophthoromyota, formerly Zygomycota) and Hypocreales (Phylum Ascomycota). These fungi are distributed in wide terrestrial ecosystems of the world including Arctic Circle and Antarctica [5]. Entomophthoralean pathogens generally show narrow host range and are distributed in temperate forests [6] with rare reports from tropical regions [7]. Hypocrealean pathogens, on the other hand, have narrow to very broad host range [4] and are dominantly distributed in humid tropical forests [7].
Cordyceps Fr. is one of the hypocrealean genera, comprising more than 400 spp. that parasitize a wide range of insects and few fungal genera. Externally, they produce clavate, cylindrical or thin filamentous, filiform stroma on the hosts. The history of exploring and identifying Cordyceps fungi is long and stretches back to the 17th century [8]. One of the most popular fungi is Ophiocordyceps sinensis (syn. Cordyceps sinensis) that grows on hepialid larvae in the alpine grasslands of the Himalayas and the Tibetan Plateau [9]. This host-fungus complex is traditionally highly revered for enhancing immunity, protecting lungs, enriching kidneys, restorative and tonic effects, treating impotence, and so forth [10–13].
Until the phylogenetic classification by Sung et al. [14], Cordyceps remained a big genus placed in family Clavicipitaceae of order Hypocreales. However, phylogenetic studies showed that neither Cordyceps nor Clavicipitaceae was monophyletic [14–18] and hence Cordyceps was segregated into several phylogenetic genera within three families of Hypocreales [14]. According to the phylogenetic classification, Cordyceps is now restricted to the clade containing the type species C. militaris, circumscribed to Cordycipitaceae [14]. Newly segregated genera Ophiocordyceps and Elaphocordyceps were placed under another family Ophiocordycipitaceae; the other two genera Metacordyceps and Tyrannicordyceps remained in Clavicipitaceae sensu stricto [14, 19].
Following the recent revision in the International Code of Nomenclature for algae, fungi, and plants (ICN), Elaphocordyceps is now synonymized with Tolypocladium [20] and Metacordyceps with Metarhizium [21]. Drechmeria, Podocrella, Polycephalomyces, and Sphaerocordyceps are other genera that consist of members that were formerly described under Cordyceps. Cordyceps along with the newly segregated genera is linked to many asexual insect-pathogenic genera distributed in all three families Clavicipitaceae s. s., Cordycipitaceae, and Ophiocordycipitaceae [4, 14, 20]. Further synonymizations of genera are recently proposed within Ophiocordycipitaceae following ICN [22].
The host range of Cordyceps in classical sense is very broad and includes several orders (Coleoptera, Lepidoptera, Hymenoptera, Hemiptera, Orthoptera, Araneae, Diptera, Blattodea, Mantodea, Dermaptera, Odonata, Phasmatodea, etc.). Based on the published literature, nearly 60% of the species of Cordyceps sensu lato are recorded on two orders Coleoptera and Lepidoptera. The other major host orders are Hymenoptera, Hemiptera, Orthoptera, and Araneae. The majority of hosts (more than 95%) in Lepidoptera (moths, butterflies) and Coleoptera (beetle) are larvae; the rest are adults or pupae, making the host identification difficult. In contrast, majority of hosts in other orders are adults such as spiders (Araneae), fly (Diptera), ant, bee, and wasp (Hymenoptera), grasshopper, locust, and cricket (Orthoptera), cicada, bug, scale-insect, and coccid (Hemiptera), cockroach and termite (Blattodea), mantis (Mantodea), earwig (Dermaptera), dragonfly (Odonata), and stick-insect (Phasmatodea). Why lepidopterans and coleopterans are mostly susceptible at larval stage while other orders are more susceptible at adult stage is not well understood.
2. Host-Pathogen Interaction
Cordyceps fungi range in habitat from aerial to epigeal to subterranean ones [74], based on their respective host species. When the host stage is adult, they grow on exposed environments such as leaf litter or are attached to some plant parts such as leaf and branch and in contrast to the larval or pupal stages that are buried in soil (hypogeal) or on wood up to nearly 50 cm, for example, O. longissima [75] and O. xuefengensis [76]. Ophiocordyceps caloceroides that is buried in the soil more than 50 cm is exceptional which grows on adult spiders [77].
The pathogenic fungi sometimes produce parasite manipulated behaviors on hosts, such as death grip or biting behavior [78–80]. Some of the parasitized ants always bite lower side veins but never the laminar blade or the upper surface [79, 80]. Similarly, some species of ants are attached to lower side of twigs whereas others are found attached to leaves [81]. In other cases, aphids, ants, grasshoppers, planthoppers, flies, and so forth shift to elevated position at the time of dying, known as summit disease [82, 83].
In this review, we present brief introductions of Coleoptera and Lepidoptera and their major subgroups parasitized by Cordyceps fungi. We hope the present review will serve as a reference for researchers and scholars to get a quick look at coleopteran and lepidopteran hosts of Cordyceps spp.
3. Materials and Methods
We accumulated host information from published literature and analysed the hosts that belonged to Coleoptera and Lepidoptera. We found that hosts of only 60% of Cordyceps fungi are known at family or genus/species ranks; the rest are known only at the order rank and hence no further discussions of the hosts could be done for them. Hence, in this review, we dealt with only those hosts that are known at family or infrafamily ranks within Coleoptera and Lepidoptera and tried to analyse the major taxonomic subgroups that are associated with Cordyceps fungi. We also analysed the host stage among coleopteran and lepidopteran hosts based on published literature.
4. Coleopteran Hosts
Coleoptera is currently the most species-rich group on this planet [84]. The order is classified into four suborders (Polyphaga, Adephaga, Myxophaga, and Archostemata) [85]. Polyphaga is the largest suborder covering 90% of total beetle species and is classified into more than 170 families. Adephaga is the second largest suborder, followed by Myxophaga and Archostemata. All the known coleopteran hosts belong to suborders Polyphaga and Adephaga under 8 superfamilies and 11 families. Short descriptions of host families are given below, followed by Cordyceps spp. recorded on them.
4.1. Superfamily Scarabaeoidea
4.1.1. Scarabaeidae
This is one of the largest families in Coleoptera and its members are commonly called scarabs or scarab beetles. Scarabaeid larvae (commonly called grubs) are short, thick, pale yellow or white, mostly live underground or under debris, and feed on dead organic matter (scavengers). Twenty-seven Cordyceps spp. are recorded in this family (Table 1). Among them, C. brittlebankii is recorded on Heteronyx sp., C. brongniartii on Anomala cuprea, C. coxii on Lepidiota sp., C. pseudoinsignis and C. velutipes on Melolontha sp., Ophiocordyceps aphodii on Aphodius howitti and A. tasmaniae, O. melolonthae on Ancyloncha puncticollis, Lachnosterna fusca, and Melolontha sp., O. michiganensis on Scarabaeus sp., O. ravenelii on L. fusca, Phyllophaga sp., and Rhizotrogus sp., and O. stylophora on Costelytra zealandica (Table 1). Other species recorded in this family are C. obliquiordinata, C. scarabaeicola, Metarhizium brittlebankisoides, Ophiocordyceps arbuscula, O. barnesii, O. elongatiperitheciata, O. geniculata, O. gracillima, O. highlandensis, O. konnoana, O. larvicola, O. macularis, O. neovolkiana, O. nigrella, O. superficialis, O. variabilis, and Sphaerocordyceps palustris (Table 1). Out of 27 Cordyceps spp., 26 are recorded on larvae except C. scarabaeicola that is recorded on adult (Table 1).
4.1.2. Geotrupidae
Members of this family are commonly called earth-boring dung beetles, which mostly excavate burrows to lay their eggs. They are normally detritivores but occasionally behave as coprophagous. Cordyceps geotrupis is recorded on an adult of Geotrupes sp. in this family (Table 1).
4.1.3. Lucanidae
Members of this family are commonly called stag beetles. The name stag beetle is derived from the distinctive mandibles found on the males that resemble the antlers of stags. The larvae feed on rotting deciduous wood for several years before pupating. Ophiocordyceps scottiana is recorded on Rhyssonotus nebulosus in this family (Table 1).
4.2. Superfamily Elateroidea
4.2.1. Elateridae
Members of this family are commonly called click beetles, elaters, snapping beetles, spring beetles, skipjacks, and so forth. The adults are typically nocturnal and phytophagous. Larvae are slender, elongate, cylindrical, or somewhat flattened, with relatively hard bodies, somewhat resembling mealworms. Fifteen spp. of Cordyceps have been recorded from this family (Table 1), all of which grow on larvae except Ophiocordyceps salebrosa that grows on an adult (Table 1). Six spp. are recorded on larvae of the following hosts: Cordyceps nirtolii on Melanotus communis, C. shanxiensis on M. caudex and Pleonomus canaliculatus, Metarhizium campsosterni on Campsosternus auratus, M. martiale on Hemirhipus sp., Ophiocordyceps jiangxiensis on C. auratus and C. fruhstorferi, and O. stylophora on Denticollis linearis (Table 1). Other spp. recorded in this family are Cordyceps aurantiaca, C. huntii, C. rubra, C. velutipes, Ophiocordyceps brunneipunctata, O. elateridicola, O. gracilioides, O. purpureostromata, and O. salebrosa (Table 1).
4.3. Superfamily Chrysomeloidea
4.3.1. Cerambycidae
The long-horned beetles, also known as longicorns, are cosmopolitan, typically characterized by extremely long antennae, which are often as long as or longer than the beetle’s body. The larvae, called roundheaded borers, bore into wood, where they can cause extensive damage to either living trees or untreated lumber. Four spp. are known from this family, all growing on larvae (Table 1). They are Ophiocordyceps dovei on Oemona hirta, O. entomorrhiza on Leptura sp., O. larvicola on Callidium sp., and O. stylophora on Phoracantha semipunctata.
4.3.2. Chrysomelidae
The family, commonly known as leaf beetle, is one of the largest beetle families. Adults and larvae feed on all sorts of plant tissues. Most chrysomelids are conspicuously colored, typically in glossy yellow to red or metallic blue-green hues. Ophiocordyceps entomorrhiza is recorded on adult of Diabrotica sp. and O. superficialis on a chrysomelid larva (Table 1).
4.4. Superfamily Cucujoidea
4.4.1. Erotylidae
It is a family of the pleasing fungus beetles. They feed on plant and fungal matter, a few of them being notable pests. Cordyceps erotyli is recorded on adult of Erotylus sp. in this family (Table 1).
4.5. Superfamily Curculionoidea
4.5.1. Curculionidae
It is the family of the true weevils or snout beetles. Weevils are almost entirely plant feeders. Cordyceps militaris is recorded on larva of Ips sexdentatus, Ophiocordyceps curculionum on adult of Heilipus celsus, O. entomorrhiza on adult of Apion flavipes, and Podocrella peltata on larva of Cryptorhynchus corticicolus (Table 1).
4.6. Superfamily Tenebrionoidea
4.6.1. Tenebrionidae
Tenebrionids are often referred to as darkling beetles as they have usually black or brown elytra and are nocturnal in habit. They are found worldwide though they are more diverse in semiarid and arid ecosystems. Adults of most species are saprophagous while larvae are mostly detritivores (litter feeders) or xylophagous. Five spp. are recorded on larvae of this family (Table 1): C. militaris on Tenebrio molitor, O. acicularis on Nictobates sp., O. entomorrhiza on Meneristes laticollis, and O. larvicola on Cylindronotus sp., Helops caraboides, and H. lanipes. Ophiocordyceps formosana is the fifth species recorded on larva of this family.
4.7. Superfamily Staphylinoidea
4.7.1. Staphylinidae
The rove beetles belong to family Staphylinidae, primarily distinguished by their short elytra. The group is currently recognized as the largest family of beetles. They are an ecologically and morphologically diverse group of beetles and commonly encountered in terrestrial ecosystems. Cordyceps memorabilis is recorded on adult of Staphylinus sp. whereas Ophiocordyceps entomorrhiza is recorded on larva of Ocypus sp. Cordyceps staphylinidicola and O. superficialis are other spp. recorded on larvae of this family (Table 1).
4.8. Superfamily Caraboidea
4.8.1. Carabidae
It is a large, cosmopolitan family. Its members are commonly known as ground beetles. They are mostly shiny black or metallic and have ridged wing covers (elytra). Common habitats are under the bark of trees, under logs, or among rocks or sand by the edge of ponds and rivers. Six spp. are known from this family (Table 1). Among them, O. entomorrhiza is recorded on adults and larvae of several species such as Carabus auronitens, C. coriaceus, C. glabratus, C. hortensis, C. intricatus, C. nemoralis, C. nemorensis, C. violaceus, Calathus sp., Calosoma sp., Coptolabrus sp., Hadrocarabus problematicus, and Pterostichus sp. Ophiocordyceps volkiana is recorded on larva of Eripus heterogaster. Cordyceps nikkoensis, Ophiocordyceps carabidicola, O. michiganensis, and O. stylophora are other species recorded on larvae of this family.
Among the coleopteran families, Scarabaeidae is parasitized by the highest number of Cordyceps fungi (27 spp.), followed by Elateridae (15 spp.) (Table 1). Among 55 parasitizing fungi (Table 1), we found that only few parasitize more than one family. For example, Ophiocordyceps entomorrhiza parasitizes 6 families, followed by O. stylophora (4 families), O. larvicola and O. superficialis (3 families each), and C. militaris, C. velutipes, and O. michiganensis (2 families each) (Table 1). From host range point of view, Ophiocordyceps entomorrhiza shows the widest range, infecting 13 spp. in Carabidae and one sp. in each Cerambycidae, Chrysomelidae, Curculionidae, Staphylinidae, and Tenebrionidae (Table 1). It is also exceptional in that it infects both larval and adult stages.
As mentioned earlier, larva is the most dominant host stage susceptible to Cordyceps pathogens in Coleoptera, with fewer adult stages being parasitized (Table 1). Besides O. entomorrhiza, six other spp. are recorded on coleopteran adults. They are C. erotyli, C. geotrupis, C. memorabilis, O. curculionum, O. salebrosa, and C. scarabaeicola; the remaining ones are recorded on larvae.
5. Lepidopteran Hosts
Lepidoptera is among the large orders of insects [121]. It has around 160,000 spp. that are classified into 4 suborders, 45 superfamilies, and 139 families [122]. Out of four suborders (Aglossata, Glossata, Heterobathmiina, and Zeugloptera), Cordyceps and allied genera are known only from Glossata. It is the largest suborder consisting of almost 99.9% of all described lepidopterans [122, 123]. It is further classified into six infraorders (Dacnonypha, Acanthoctesia, Lophocoronina, Neopseustina, Exoporia, and Heteroneura) [122]. Among them, Cordyceps hosts are known from two infraorders Exoporia and Heteroneura.
Lepidopterans have from three to more than a dozen larval instars (caterpillars), often five [123, 124], inhabiting as root- or stem-borers or foliage eaters and leaf-miners of angiosperms, usually within narrow range of host plants. Lepidopterans have distinct feeding habits, basically plant-feeding during larval stage and nectar-feeding during adult stage. Exoporia and Heteroneura are discussed below in short, followed by Cordyceps pathogens parasitizing them.
5.1. Infraorder Exoporia
It is a small infraorder consisting of 636 spp. that are classified into 2 superfamilies [122]. Cordyceps and allied genera are recorded only from the superfamily Hepialoidea. The superfamily comprises five families that are distributed in diverse vegetation such as forest, shrubland, grassland, tundra, swamp, and bog with the most varied diet habit among moth families [123, 125]. Among the families, Cordyceps spp. are recorded from family Hepialidae alone (Table 2).
Ophiocordyceps sinensis has the widest host range recorded on Hepialidae, covering 55 spp. [95, 96]. Among them, Thitarodes and Ahamus are the two major genera (Table 2). Thirty-two spp. of Thitarodes (T. albipictus, T. armoricanus, T. baimaensis, T. baqingensis, T. bibelteus, T. biruensis, T. callinivalis, T. cingulatus, T. damxungensis, T. deqinensis, T. dongyuensis, T. ferrugineus, T. gonggaensis, T. jialangensis, T. jinshaensis, T. kangdingensis, T. kangdingroides, T. latitegumenus, T. litangensis, T. markamensis, T. meiliensis, T. namensis, T. namlinensis, T. oblifurcus, T. pratensis, T. pui, T. renzhiensis, T. varians, T. xunhuaensis, T. yeriensis, T. zaliensis, and T. zhongzhiensis) and 13 spp. of Ahamus (A. anomopterus, A. gangcaensis, A. jianchuanensis, A. lijiangensis, A. luquensis, A. maquensis, A. sichuanus, A. yulongensis, A. yunlongensis, A. yunnanensis, A. yushuensis, A. zadoiensis, and A. zhayuensis) are the host species of Ophiocordyceps sinensis (Table 2). The other host species are Pharmacis carna, P. fusconebulosa, P. pyrenaicus, Magnificus jiuzhiensis, M. zhiduoensis, Bipectilus yunnanensis, Endoclita davidi, Gazoryctra ganna, Parahepialus nebulosus, and Hepialus xiaojinensis (Table 2).
There are other species that share similar hosts as Ophiocordyceps sinensis. For example, O. crassispora and C. kurijimeansis are recorded on Thitarodes baimaensis and T. armoricanus, respectively (Table 2). Ophiocordyceps gracilis, O. lanpingensis, and O. laojunshanensis are recorded on Ahamus altaicola, A. jianchuanensis, and A. yunnanensis, respectively (Table 2). Ophiocordyceps gracilis is also recorded on three more hosts Hepialus humuli, Korscheltellus lupulina, and Parahepialus nebulosus. Similarly, Cordyceps hepialidicola is reported on Endoclita excrescens and O. ramosissimum and O. xuefengensis on Endoclita nodus (Table 2).
Many species are recorded in Australia and New Zealand on hepialid hosts. For instance, Cordyceps cranstounii, C. hawkesii, D. gunnii, O. robertsii, and O. taylorii are recorded on Abantiades labyrinthicus and other Abantiades spp., Aenetus virescens, Aoraia dinodes, A. ensyii, Dasypodia selenophora, Oxycanus dirempta, and other Oxycanus spp., Trictena atripalpis and other Trictena spp., Wiseana spp., and so forth (Table 2). Another Cordyceps sp. rarely described on Hepialus is C. militaris (Table 2). Besides that, Cordyceps cuncunae and O. emeiensis are also recorded on hepialid hosts (Table 2).
5.2. Infraorder Heteroneura
This infraorder consists of more than 98% of lepidopteran species [122]. Nine superfamilies among more than 30 in the infraorder are recorded as hosts of Cordyceps spp. Among the host families, Tineidae is the only microlepidopteran family; the rest are macrolepidopterans. Papilionidae and Pieridae are the two butterfly families, the rest being moths. The host families are briefly described below followed by Cordyceps spp. recorded on them.
5.2.1. Superfamily Noctuoidea
(1) Erebidae. It is the largest family in Lepidoptera with 24,569 described spp. [122]. Despite the high species richness, only two Cordyceps spp. are recorded on this family. Of them, C. militaris is recorded on Calliteara pudibunda and Leucoma salicis whereas C. nikkoensis is reported on a larva of the family (Table 3).
(2) Noctuidae. It is commonly known as owlet moths. Cordyceps militaris is recorded on 4 spp. of this family: Arcte coerula, Colocasia coryli, Euxoa ochrogaster, and Panolis flammea (Table 3). Ophiocordyceps elongata is recorded on Acronicta americana. Other species recorded in this family are Cordyceps alpicola, C. bifusispora, C. bulolensis, C. cristata, and C. tuberculata (Table 3).
(3) Notodontidae. Its members are mainly concentrated in the tropical areas. Some examples of this family are puss moths. Cordyceps militaris is recorded on 5 spp. of this family. They are Fentonia ocypete, Lampronadata cristata, Phalera assimilis, P. bucephala, and Syntypistis punctatella (Table 3).
5.2.2. Superfamily Zygaenoidea
(1) Limacodidae (Cochlididae). The members of this family are known as slug moths and are mostly tropical. Ophiocordyceps cochlidiicola is recorded on larva and pupa of this family (Table 3).
5.2.3. Superfamily Cossoidea
(1) Cossidae. The members are known as carpenter millers and are found worldwide. Four spp. are recorded in this family. Of them, Metarhizium indigoticum is recorded on Yakudza vicarius. Two recently described spp., Ophiocordyceps arborescens and O. macroacicularis, are recorded on Cossus sp. (Table 3). The other species recorded on this family is Cordyceps bassiana.
5.2.4. Superfamily Drepanoidea
(1) Drepanidae. The members of this family have worldwide distribution. Cordyceps militaris is recorded on 4 spp. of this family: Achlya flavicornis, Ochropacha duplaris, Tethea ocularis, and Tetheella fluctuosa (Table 3).
5.2.5. Superfamily Tineoidea
(1) Tineidae. The members are small to medium-sized moths. They are worldwide in distribution but are particularly common in the Palaeartic ecozone. Cordyceps cardinalis is recorded on larva of this family (Table 3).
5.2.6. Superfamily Papilionoidea
(1) Papilionidae. It is a family of colorful swallowtail butterflies. Some of the members are the largest butterflies in the world. The majority are distributed in the tropical region. Cordyceps tuberculata is reported on adult of this family (Table 3).
(2) Pieridae. It is a large family of butterfly, mostly distributed in the tropical parts of the world. Its members are mostly white, orange, or yellow in pigmentation. Metarhizium taii is reported on Pieris rapae in this family (Table 3).
5.2.7. Superfamily Geometroidea
(1) Geometridae. It is the second largest family in Lepidoptera with 23,002 spp. [122]. It is commonly known as inch worms. Some of the members are notorious pests. Cordyceps militaris and C. riverae are recorded from this family parasitizing Biston panterinaria, Lycia hirtaria, and Triphosa sp. (Table 3).
5.2.8. Superfamily Bombycoidea
(1) Bombycidae. It is known as silkworm family. The most well-known member is Bombyx mori, native to northern China. Cordyceps militaris is recorded on B. mori and C. michaelisii on a species of Bombyx (Table 3).
(2) Endromidae. This is a small family. Cordyceps militaris is recorded on Andraca bipunctata in this family (Table 3).
(3) Saturniidae. The members include giant silk moths, royal moths, and emperor moths. They are described worldwide but are particularly known from tropical and subtropical regions. Some of the members are the largest moth species. Cordyceps longdongensis parasitizes Actias artemis whereas C. militaris parasitizes Anisota senatoria (Table 3).
(4) Sphingidae. The members of this family are commonly known as hawk moths or sphinx moths. They are moderate to large in size and are mainly described from the tropical parts. Cordyceps militaris is recorded on various species in this family such as Callambulyx tatarinovii, Laothoe populi, Marumba sperchius, Mimas tiliae, Hyles euphorbiae, and Sphinx pinastri and C. tuberculata on Amphipyra effusa, Amphonyx duponchel, A. jatrophae, Anceryx ello, Cocytius sp., Macroglossum insipida, and S. pinastri. Two other spp. Cordyceps kyusyuensis and C. taishanensis are recorded on Clanis bilineata. Cordyceps flavobrunnescens and C. polyarthra are other spp. recorded from this family.
5.2.9. Superfamily Lasiocampoidea
(1) Lasiocampidae. Its members are known as snout moths or lappet moths. They are large in size with broad wings and are known worldwide. Cordyceps militaris is reported on Dendrolimus pini, D. superans, and Macrothylacia rubi (Table 3).
Out of 22 spp. recorded on heteroneuran hosts (Table 3), C. militaris has the widest host range, extending to 2 infraorders, 6 superfamilies, 10 families, and 29 spp. (Table 3). It is a cosmopolitan species, distributed from sea level to more than 2000 m above sea level [126]. Probably due to its wide host range and adaptability to wider habitats, this species demonstrates rapid in vitro growth and fructifications [127]. Cordyceps tuberculata is another species recorded on multiple families. Larva is the most suitable host for Cordyceps spp. compared to pupa and adult (Table 3).
In total, 16 families in Lepidoptera (1 exoporian and 15 heteroneuran) are identified as host families of Cordyceps and allied genera. Hepialidae, though a small family, hosts 6 Cordyceps spp., 1 Drechmeria sp., and 10 Ophiocordyceps spp. (Table 2). They are mostly distributed in either Asia or Australia/New Zealand. After Hepialidae, Noctuidae and Sphingidae are the families mostly infected by Cordyceps spp. (Table 3).
Among heteroneuran families, Notodontidae, Drepanidae, and Lasiocampidae are known as hosts of C. militaris only (Table 3). Similarly, there are families identified as hosts for single Cordyceps/Ophiocordyceps spp., for example, Limacodidae (Cochlididae) for O. cochlidiicola, Tineidae for C. cardinalis, Papilionidae for C. tuberculata, and Pieridae for C. taii. In general, 11 families are known for just one or two Cordyceps spp. (Table 3). On the other hand, a single host species is infected by two spp. such as Clanis bilineata by Cordyceps kyusyuensis and C. taishanensis, Sphinx pinastri by C. militaris and C. tuberculata, Ahamus yunnanensis by Ophiocordyceps lanpingensis and O. laojunshanensis, and Endoclita nodus by O. ramosissimum and O. xuefengensis. From species richness point of view, Erebidae, Geometridae, and Noctuidae are the biggest families in Lepidoptera that occupy nearly 40% of the total lepidopterans [122]. However, they are reported with fewer Cordyceps pathogens. For instance, only two Cordyceps spp. are recorded on each Erebidae and Geometridae, proportionately more on Noctuidae (7 spp.) (Table 3). In addition to Coleoptera and Lepidoptera, C. militaris is recorded on two more orders Diptera and Hymenoptera [126]. Similarly, the only other species growing on two orders Lepidoptera and Coleoptera is C. nikkoensis.
The analysis in the present review is based on the coleopteran and lepidopteran hosts that are identified at family or infrafamily ranks in the literature. Out of estimated 200 spp. reported on coleopteran and lepidopteran hosts, we have enlisted 92 spp. based on their host records in the literature. We could not include the remaining species because of lack of information on infraorder ranks of their hosts. Though the list is not complete for all Coleoptera and lepidopteran hosts, the overall scenario of the taxonomic distributions of the hosts within Coleoptera and Lepidoptera can be viewed in the present review.
6. Further Studies on Hosts of Cordyceps Pathogens
Cordyceps fungi with attached hosts have long been studied as botanical or mycological specimens. Mycologists have studied and identified fungal pathogens of insects based on morphological, ecological, and phylogenetic studies [14, 50, 128]. For interested readers, several color books on entomopathogenic fungi are available [59, 129–142]. However, identification of the host species is far from being complete. Some of the possible reasons for the less work on host identification are discussed here. First, the diseased/damaged/deformed insect specimens hinder the objectives of the insect biologists to study their diversity and life cycle and thus are disposed immediately after encountering them [77]. Second, insects are mostly attacked at larval stage, making the identification more difficult and time consuming. Larval stages are not yet described in most of insect species. However, molecular techniques have been recently developed to identify immature stages of insects [143]. Third, Cordyceps pathogens of insects rarely cause epizootic outbreaks on their hosts, hence causing no significant economic or ecological losses. Fourth, finding a Cordyceps pathogen requires much experience and patience and is out of sight for normal observers. Fifth, Cordyceps pathogens are specialists; that is, they are host specific; hence experts interested in one group of insects need not care about pathogens on insects of noninterest groups.
Exploring the potential economic benefit from Cordyceps fungi is a continuous objective of mycologists in collaboration with biotechnologists, pharmacologists, analytical chemists, medical scientists, and so forth. The most common example is Ophiocordyceps sinensis. This is the fungal entomopathogen collected every year in large quantities [144–148] and sold worldwide as the most expensive biological resource almost twice the value of gold by weight and hence commonly known as Himalayan Gold [149], Tibetan Gold (http://mushroaming.com/content/yartsa-gunbu-article-national-geographic-magazine), or Biological Gold [147]. The other potential species is Cordyceps militaris that has been successfully grown on artificial media for commercial purpose [126]. Antitumour, antimetastatic, immunomodulatory, antioxidant, anti-inflammatory, insecticidal, antimicrobial, hypolipidaemic, hypoglycaemic, antiaging, neuroprotective, and renoprotective effects are some of the main effects shown by Cordyceps fungi [150].
Insect specimens, decaying or mummified with natural enemies, such as virus, bacteria, and fungi, are the good sources of biological control agents of specific insect groups, especially in agriculture, forests, and other natural communities. For example, the susceptible stages of hosts in nature could be informative for the application of entomopathogenic fungi to control harmful insect and pests.
In conclusion, we believe such reviews will attract wider audience towards economic and ecological benefits of entomopathogenic fungi including Cordyceps, paving the way for interdisciplinary collaborations. Such reviews will also generate interest in a wider audience including field entomologists, ecologists, biocontrol researchers, and biotechnologists in utilization of entomopathogenic fungi. The accumulative work on host information of other orders parasitized by Cordyceps and its asexual genera is going on with the objective of expanding the insect-fungal pathogen index in future.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
This work was supported by the research program of agricultural science and technology development (PJ008523) of the National Institute of Horticultural and Herbal Science and by Korea National Arboretum (Project no. KNA 1-1-10).