Abstract
Simple SummaryThe Chinese cordyceps is a valuable parasitic Ophiocordyceps sinensis fungus–Thitarodes/Hepialus larva complex. In view of culturing this complex, a method for the artificial rearing of the Thitarodes/Hepialus ghost moth hosts was established. Deterioration of the host insect population and low mummification rates in infected larvae constrain effective cultivation. Hybridization of Thitarodes/Hepialus populations may overcome this problem. Thitarodes shambalaensis and Thitarodes sp. were inbred or hybridized, and the biological parameters, larval sensitivity to the fungal infection and mitochondrial genomes of the resulting populations were investigated. Hybridization of T. shambalaensis and Thitarodes sp. allowed producing a new generation. One hybrid population (T. shambalaensis females mated with Thitarodes sp. males) showed increased population growth as compared with the parental Thitarodes sp. population. The sensitivity of the inbred larval populations to four fungal isolates of O. sinensis differed. The complete mitochondrial genomes of T. shambalaensis, Thitarodes sp. and the hybrid population were 15,612 bp, 15,389 bp and 15,496 bp in length, respectively. A + T-rich regions were variable in sizes and repetitive sequences. The hybrid population was located in the same clade with T. shambalaensis, implying the maternal inheritance of mitochondrial DNA.The Chinese cordyceps, a parasitic Ophiocordyceps sinensis fungus–Thitarodes/Hepialus larva complex, is a valuable biological resource endemic to the Tibetan Plateau. Protection of the Plateau environment and huge market demand make it necessary to culture this complex in an artificial system. A method for the large-scale artificial rearing of the Thitarodes/Hepialus insect host has been established. However, the deterioration of the insect rearing population and low mummification of the infected larvae by the fungus constrain effective commercial cultivation. Hybridization of Thitarodes/Hepialus populations may be needed to overcome this problem. The species T. shambalaensis (GG♂ × GG♀) and an undescribed Thitarodes species (SD♂ × SD♀) were inbred or hybridized to evaluate the biological parameters, larval sensitivity to the fungal infection and mitochondrial genomes of the resulting populations. The two parental Thitarodes species exhibited significant differences in adult fresh weights and body lengths but not in pupal emergence rates. Hybridization of T. shambalaensis and Thitarodes sp. allowed producing a new generation. The SD♂ × GG♀ population showed a higher population trend index than the SD♂ × SD♀ population, implying increased population growth compared with the male parent. The sensitivity of the inbred larval populations to four fungal isolates of O. sinensis also differed. This provides possibilities to create Thitarodes/Hepialus populations with increased growth potential for the improved artificial production of the insect hosts. The mitochondrial genomes of GG♂ × GG♀, SD♂ × SD♀ and SD♂ × GG♀ were 15,612 bp, 15,389 bp and 15,496 bp in length, with an A + T content of 80.92%, 82.35% and 80.87%, respectively. The A + T-rich region contains 787 bp with two 114 bp repetitive sequences, 554 bp without repetitive sequences and 673 bp without repetitive sequences in GG♂ × GG♀, SD♂ × SD♀ and SD♂ × GG♀, respectively. The hybrid population (SD♂ × GG♀) was located in the same clade with GG♂ × GG♀, based on the phylogenetic tree constructed by 13 PCGs, implying the maternal inheritance of mitochondrial DNA.
Highlights
The Chinese cordyceps (Ophiocordyceps sinensis fungus–Thitarodes larva complex) is a valued biological resource endemic to the Tibetan Plateau and widely used in medicinal treatments including fatigue, asthma, respiratory and kidney diseases and as health foods, especially in many Asian countries [1,2,3,4]
Comparative phylogenetic analyses have suggested coevolutionary relationships between O. sinensis and its host insects [14,15]. It appears that most host insect species of the O. sinensis fungus have a very narrow distribution on the Tibetan Plateau, and host insect species might vary among different mountain ranges and even from different sides and habitats of the same mountain [16]
The developmental performance of the studied Thitarodes populations was influenced by the hybridization, whereas the larval sensitivity to the fungal infection of the inbred populations was affected by the parental populations
Summary
The Chinese cordyceps (Ophiocordyceps sinensis fungus–Thitarodes larva complex) is a valued biological resource endemic to the Tibetan Plateau and widely used in medicinal treatments including fatigue, asthma, respiratory and kidney diseases and as health foods, especially in many Asian countries [1,2,3,4]. Comparative phylogenetic analyses have suggested coevolutionary relationships between O. sinensis and its host insects [14,15]. It appears that most host insect species of the O. sinensis fungus have a very narrow distribution on the Tibetan Plateau, and host insect species might vary among different mountain ranges and even from different sides and habitats of the same mountain [16]. Given the complex and harsh ecological environment in the Tibetan Plateau, most Hepialidae species have a narrow-area distribution type [21]. Of ninety-one named Hepialidae insects spanning thirteen genera reported to be related to host insects of the O. sinensis fungus, fifty-seven are considered potential host species of the fungus and are distributed throughout the Tibetan Plateau [17]. The described insect host species or strains of O. sinensis have never been confirmed by a hybridization technique
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