Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 March 2021 | 13(3): 18030–18034
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
https://doi.org/10.11609/jott.5157.13.3.18030-18034
#5157 | Received 09 June 2019 | Final
received 12 November 2020 | Finally accepted 05 March 2021
Potential phytophagous insects of
Pteridium revolutum
(Blume) Nakai, an invasive fern
M.S. Arjun 1 & S. Gopakumar
2
1,2 Department of Natural Resource
Management, College of Forestry, Kerala Agricultural University, Thrissur,
Kerala 680656, India.
1 arjunms001@gmail.com, 2 gopan.s@kau.in
(corresponding author)
Editor: Anonymity
requested. Date of publication:
26 March 2021 (online & print)
Citation: Arjun, M.S. & S. Gopakumar (2021). Potential
phytophagous insects of Pteridium revolutum (Blume) Nakai, an
invasive fern. Journal of Threatened Taxa 13(3): 18030–18034. https://doi.org/10.11609/jott.5157.13.3.18030-18034
Copyright: © Arjun & Gopakumar 2021. Creative
Commons Attribution 4.0 International License.
JoTT allows unrestricted use, reproduction,
and distribution of this article in any medium by providing adequate credit to
the author(s) and the source of publication.
Funding: Self funded.
Competing interests: The authors
declare no competing interests.
Acknowledgements: The authors gratefully
acknowledge the contributions by Dr. Mani Chellapan,
Professor and Head, Department of Agricultural Entomology of College of
Horticulture, KAU P. O. Thrissur in identifying the insect larvae.
Abstract: The article reports an
observation on the phytophagous behaviour by the insect larvae of two insect
species on a fern, Pteridium revolutum, which is fast emerging as an invasive plant
species threatening local biodiversity and wildlife in Kerala State, India.
Keywords: Biological control, phytophagous
nature, Pteridium, Western Ghats.
Bracken ferns (genus Pteridium) represent an ancient species complex with
a natural worldwide distribution (Der et al. 2009). Notorious as weeds because of its exceptional
ability to grow rhizomatously in dense patches, these
ferns are widely reported to overgrow in open fields and pastures (Tryon 1941;
Holm et al. 1997). Invasiveness of these
clonally growing ferns is attributed to their vigorous vegetative propagation ability and genetic variability (Zhou et al.
2014). Pteridium
revolutum (Blume) Nakai
has reported distribution in diverse ecosystems in India, Sri Lanka, China,
Taiwan, southern Japan, Myanmar, the Philippines, Thailand, throughout southeastern Asia, New Guinea, and Australia (Ranil et al. 2010; Deepa et al. 2013). In tropical and subtropical areas of Asia,
above 1,000m, P. revolutum is
perennial with fronds that grow from the robust underground rhizomes, reaching
over 1m in height (Zheng et al. 2008).
In Chinese medicine, rhizomes of this fern have uses and the fronds are
regarded to be attractive to the landscape (Zhang & Zhang 1986).
Toxic effects on herbivores
Many workers like Smith (1990) and Taylor (1990) have
reported that in China, the Bracken Fern Pteridium
sp. is a very common plant and is often browsed by domestic herbivores,
developing several syndromes. Enzootic
haematuria, the clinical name of the urinary bladder neoplasia of ruminants
(bovine enzootic haematuria), tends to occur persistently in localized bracken
infested regions throughout the world.
In China, enzootic haematuria of cattle was observed in almost all the
provinces where P. revolutum occurred,
but the disease has not been reported outside of these regions (Leren 1989; Xu 1992).
Furthermore, in areas where enzootic haematuria was found, the disease
usually occured in highland or mountainous areas at
950–2,000 m where conditions are suitable for the growth of P. revolutum (Xu 1986).
Consumption of this fern has also been reported to cause urinary bladder
cancer in ruminants. It is also associated
with carcinoma of the upper digestive tract of cattle, where it is believed to
be caused by the malignant transformation of the bovine papilloma (Jarrett
1987). The major carcinogen of bracken
has been identified as Ptaquiloside, a norsesquiterpenoid glycoside (Niwa
et al. 1983; Hirono et al. 1984). This readily undergoes glucose elimination to
form an unstable conjugated dieneone intermediate
capable of alkylating amino acids and DNA (Fletcher et al. 2011). The mutagenicity (Nagao et al. 1989), clastogenicity (Matsuoka et al. 1989), and carcinogenicity
(Hirono et al. 1984) of ptaquiloside
have been well demonstrated. Bracken has
also been associated with livestock poisoning causing bone marrow damage
leading to a fatal hemorrhagic disease of cattle (“Bracken”
poisoning), and “bracken staggers” of horses (an effect of thiaminase). Fenwick (1989) had drawn attention to the
possibility of indirect consumption of the Bracken carcinogen which may cause
or increase the risk of cancer in man.
Pteridium revolutum
Rhizomes long-creeping, hairy, subterranean. Stipes and rachises dull yellow brown,
bearing abundant non-glandular hairs, stipes 25–60 cm long, 3–6 mm diameter,
hard. Laminae broadly ovate or
triangular to broader than long, 100 x 30–90 cm, 3-pinnate at base, leathery,
dull light green on both surfaces, not mealy on underside. Primary pinnae arising at narrow angles to
rachis, the longest 18–60 x 8–45 cm.
Secondary pinnae arising at wide angles, the longest 4–25 x 1–4 cm;
midribs of primary and secondary pinnae lacking free lobes or wings. Tertiary pinnae all equal in length on each
secondary pinna, the longest 0.6–2.5 x 0.3–0.5 cm. Ultimate segments linear, slightly falcate,
acute, entire, adnate. Upper lamina
surface sparsely hairy along midribs, lower with dense, colourless, spreading,
non-glandular hairs throughout. Reflexed
lamina margins protecting sori membranous, fimbriate
and hairy (Brownsey 1989).
Natural enemies on Pteridium
revolutum
Generally, the fern is considered unpalatable to many
animal and insect species due to the presence of toxic secondary metabolites
like ptaquiloside, however, we observed two “natural
insect feeders” relishing on bracken population in the Chembra
and Thirunelly areas in Wayanad District, Kerala
State, India. Similar observations could
also be noted at Thrissur District (Vazhachal high
altitude region) and Gavi (Periyar Tiger Reserve
area) in Kerala State, India. During a
survey on the distribution of Pteridium in
Kerala, insect larvae seen feeding on this fern were collected and carried to
the lab for identification. The feeding
nature, extent of damage caused etc were carefully observed and recorded. The collected specimens were later identified
as the larvae of two insect species namely, Spilosoma
obliqua (Lepidoptera: Arctiidae)
and Tetragonus catamitus
(Callidulidae) with the help of insect taxonomists at
Kerala Agricultural University (KAU), Kerala State, India.
Spilosoma obliqua
Spilosoma obliqua Walker (Syn. Diacrisia
obliqua) (Lepidoptera: Arctiidae),
commonly known in Asia as the Bihar hairy caterpillar, is a sporadic but
polyphagous plant pest that occurs in Bangladesh, Myanmar, India, Pakistan, and
Sri Lanka (Singh & Sehgal 1992). The
larvae of this species were found feeding on the frond
of the bracken fern in the observed areas.
According to Warad & Kalleshwara (2017), the young larvae are translucent light
yellow with dark big head (Plate1). The
larval body has number of long hairs arising from dark coloured tubercles. Once fully grown, it is more stout and
cylindrical with conspicuous dark anterior and posterior patches. Pupation occurs in the soil. The adults are medium sized brown moths and
have pink abdomen with wings pinkish with numerous black spots. The antennae and legs are light brown. The average longevity of the adult male is
4–5 days with an average of 4.40 days.
The female is bigger than the male.
The abdomen of female is blunt, while the abdomen of male is narrower
and pointed.
Tetragonus catamitus
T. catamitus, though easily identifiable, are difficult to observe
in the field but have been reported from Kerala (Sondhi
et al. 2018). Since the larvae of T.
catamitus feed on ferns, they are
also known as Fern Moth. Holloway (1998)
also mentions that it hosts on genus Drynaria and
further mentioned that T. catamitus in
Hong Kong hosts on Pteridium (unpublished
Initial Environmental Examination Report).
Their eggs are very flat, scale-like (Holloway
1998). Eggs are laid on the underside of fronds or the young stalk of the
host plant. Larvae start feeding from the tip of the pinnae and it seems that
their strong mandibles help them to eat the central veins. The head and first thoracic segment of the
larvae are black and they have well-developed, chitinous, shiny, black prothoracic
shields, which are separated by a median green line. The same line splits
into two at the base of the head carapace and extends towards the forehead
forming a ‘V’ shaped mark. Larvae have
grass green, translucent bodies. The
head of the observed specimen had two symmetrical pale-whitish triangular
patches besides the ‘V’ shaped marking.
The head and prothoracic shield on the first thoracic bore several
whitish, translucent bristles of various sizes.
The pupa is a medium-sized cocoon of an elongated narrow ovate shape,
chocolate brown in colour; with a prominent head, which is thickest in the
middle, a parallel-sided abdomen forms a cone at the last four segments.
Potential bio-control agents of Bracken Fern
Even though Bracken Fern’s foliage has been reported
to possess toxicity, we noticed profuse feeding by these two insect larvae in
Wayanad District, Kerala State, India.
The frond which was being eaten by these two larvae was neither juvenile
nor too mature. While T. catamitus larvae were observed as feeding on both
the veins and leafy portions, S. obliqua
were avoiding the veins and feeding only on the leaf portion. S. obliqua
larvae also left a net-like structure around the frond on which it
fed. We noticed that S. obliqua larvae created more damage compared
to T. catamitus larvae. The feeding pattern of both the larvae was
also noticeably different. The larva of S. obliqua
seems to be concentrating on one frond at a time. As they could not chew the whole frond, some
pinnules were left unaffected by the larvae.
On the other hand, T. catamitus
fed at random. Further, the larvae
of T. catamitus were observed to use the fern
frond to make pupa and finally to moth. S.
obliqua used the fern only for feeding and no
sign of any pupa formation in the frond could be seen. The net-like structure caused by the S.
oblique could make the frond vulnerable in case of forest fire.
Conclusion
We have observed the ‘invasiveness’ of the Bracken or
Eagle Fern Pteridium revolutum
in the forest ecosystems of Wayanad, Thrissur, and Pathanamthitta
districts of Kerala State, India. The
threat of this fern is more in the higher altitudes of the Western Ghats
landscape, where the unique grassland ecosystem thrives. The phytotoxicity of this ‘weed’ and its
impact on native flora and foraging fauna, including wild herbivores must be
researched and conclusions drawn to shape their management strategies. As P. revolutum
possess a long, wide creeping rhizome, its mechanical or physical method of
management has severe limitations. On
the other hand, any disturbance to its root zone will help the weed to
establish more aggressively. P. revolutum
is also highly resistant to drought and fire, which is another favourable trait of its invasiveness. In the light of
these, the potential role of the larvae of Spilosoma
oblique (Lepidoptera: Arctiidae) and Tetragonus catamitus
(Callidulidae) to manage this invasive fern merits
immediate consideration.
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