The tropical rainforests of Sundaland are a global biodiversity hotspot increasingly threatened by human activities. While parasitic insects are an important component of the ecosystem, their diversity and parasite-host relations are poorly understood in the tropics. We investigated parasites of passerine birds, the chewing lice of the speciose genus
Myrsidea
Waterston, 1915
(Phthiraptera: Menoponidae) in a natural rainforest community of Malaysian Borneo. Based on morphology, we registered 10 species of lice from 14 bird species of six different host families. This indicated a high degree of host specificity and that the complexity of the system could be underestimated with the potential for cryptic lineages/species to be present. We tested the species boundaries by combining morphological, genetic and host speciation diversity. The phylogenetic relationships of lice were investigated by analyzing the partial mitochondrial cytochrome oxidase I (
COI
) and the nuclear elongation factor alpha (
EF-1α
) genes sequences of the species. This revealed a monophyletic group of
Myrsidea
lineages from seven hosts of the avian family Pycnonotidae, one host of Timaliidae and one host of Pellorneidae. However, species delimitation methods supported the species boundaries hypothesized by morphological studies and confirmed that four species of
Myrsidea
are not single host specific. Cophylogenetic analysis by both distance-based test ParaFit and event-based method Jane confirmed overall congruence between the phylogenies of
Myrsidea
and their hosts. In total we recorded three cospeciation events for 14 host-parasite associations. However only one host-parasite link (
M. carmenae
and their hosts
Terpsiphone affinis
and
Hypothymis azurea)
was significant after the multiple testing correction in ParaFit.
Four new species are described:
Myrsidea carmenae
sp.n.
ex
Hypothymis azurea
and
Terpsiphone affinis
,
Myrsidea franciscae
sp.n.
ex
Rhipidura javanica
,
Myrsidea ramoni
sp.n.
ex
Copsychus malabaricus stricklandii
, and
Myrsidea victoriae
sp.n.
ex.
Turdinus sepiarius
.
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