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Subfamilies of the Noctuidae included in this part of The Moths of Borneo
are often referred to as the Trifinae because of the condition of the
hindwing venation they mostly share: loss of vein M2 such that the
posterior angle of the cell has only three veins arising from it, M3, CuA1
and CuA2. The group would appear to be a natural one, though
classification of subfamilies within it is not satisfactory.
The
trifines are of great interest for several reasons. The most important is
that they have been highly successful at moving into, and diversifying
within, open habitats, feeding on herbaceous plants. Many are highly
dispersive, sometimes migratory, being quick to colonise ephemeral, weedy
habitats, the early stages in vegetational succession. They form a major
component of the faunas of isolated tropical islands, such as those of
Polynesia, and the major component of faunas at high latitudes.
This
versatility has brought many of them into conflict with man. Some of the
most devastating pests in tropical agriculture are trifine noctuids:
cutworms, armyworms, earworms and stem borers.
Their predominance at high latitutes is reflected
in the tropics at high altitudes, where they are the predominant noctuid
group. In Borneo most of the Noctuidae found only on G. Kinabalu are
trifines, including the only noctuid of the small summit element, Diarsia
barlowi Holloway.
The
Trifinae as a natural group
Kitching (1984) suggested that the trifine subfamilies, together with
the pantheinae, were held together on rather dubious grounds mostly the
loss of vein M2 in the hindwing (Figure 1). Even this venation character
is not seen in all currently recognised trifines. M2 is present in the
Pantheinae and in genera of the Amphipyrini such as Bagada Walker, Condica
Walker, Callopistria Hubner, Dipterygina Sugi, Lignispalta
Gen. n., Mudaria Moore, and Yula Bethune-Baker.
Nevertheless
there are other features that suggest that the majority of trifine genera
do form a natural group and at some subgroups can be recognised.
The
most important feature is the pair of hair pencils located in the base of
the male abdomen. These have been discussed in detail by Birch (1972,
1979) and arise from the anterior of the basal sternite as sclerotised
bands (the levers) that extend anteriorly lateral to the sternite to
terminate each in a plate from which arises the scent pencil, a tuft of
long hair-scales. Associated with each lever is a small glandular
structure, Stobbe's gland. The scent pencils are enfolded in elongated
pouches set laterally in more posterior sternites, and are only displayed
during courtship. They are illustrated in Figs. 2-7. The complexity of
this structure is such that it provides a strong synapomorphy for trifine
groups. It is found in Agaristinae, Hadeninae, Noctuinae, Cuculliinae,
Amphipyrinae, Heliothinae and Stiriinae. It is not
found in the Acronictinae, and is only seen in Elydnodes Hampson of
the Pantheinae, a probably polyphyletic group (Holloway, 1985).
Figure
1.
Quadrifine (Stictoptera, left) and trifine (Spodoptera, right)
hindwing venation. The arrow indicates vein M2 or the fold marking its
position.
Several
or many genera of each of these subfamilies lack the basal hair pencils,
and they may be variably present within a genus (e.g. Mythimna Ochsenheimer).
It is therefore difficult to assess whether the generally plesiomorphic
Amphipyrini genera without them never had them or have secondarily lost
them.
The
next feature of interest is the ornamentation of the bursa by
longitudinal, scobinate, band-like signa, often up to four in number, very
rarely more. If this is considered apomorphic to the fine, general
scobination seen in the bursa in many Amphipyrini, Acronictinae and
Agaristinae, it serves to group together the Noctuinae, Hadeninae,
Cuculliinae, Apameini (of the Amphipyrinae) and the Heliothinae and
Stiriinae. In many genera of these they are lost or otherwise modified,
but occur with sufficient frequency to suggest that these subfamilies
might form a natural group.
Matthews
(1988) discusses in detail the probable sister-relationship between the
Stiriinae and Heliothinae. The larvae have a characteristically spiny skin
and are flower, seed and fruit feeders in both groups. The harpe arises
simply from the sacculus in a rather basal position as in Amphipyrini,
Acronictinae and Agaristinae.
The
Noctuinae, Hadeninae, Cuculliinae and Apameini mostly show variations on a
different type of harpe. It occurs more distally on the valve and more
towards the costa, and overlaps a process from the costa that extends
across the interior lamina of the valve towards the ventral margin, often
making the harpe appear bifid or trifid. The feature is seen most clearly
in Diarsia Hubner (Noctuinae), Mythimna (Hadeninae) and Apamea
Ochsenheimer (Apameini). It is often associated with development of
the valve apex into a cucullus, a paddle-shaped structure, fringed
distally by the corona and often bearing further stout spines on the
interior. The groups showing this feature will be referred to subsequently
as the 'higher trifines'.
Other
features of adult morphology which might repay investigation are: the
presence of a coronal row of stout setae at the valve apex, seen widely in
trifine groups but probably absent from quadrifine groups; development of
a strongly setose peniculus (the ventral part of each side of the tegumen);
the presence of lateral rods to the male eighth sternite, seen widely in
all except the higher trifines, but not surveyed in the quadrifines. In
the higher trifines there is a tendency for the basal sternite of the
abdomen to become wider and shorter (see Figs. 11, 12 compared with Figs
13, 14, 18), with the apodemes more widely separated. The aedeagus vesica
is, in general, very much longer in the groups with the apomorphic state
of the female bursa, and is correlated with marked development of the
appendix bursae. In most higher trifines and a few 'lower' ones (e.g. Condica
Walker, Sasunaga Moore) the male eighth tergite has two longitudinal
bands of sclerotisation that are fused anteriorly, thence diverge and
broaden posteriorly to be bridged distally by a broad, rather diffuse,
transverse zone of sclerotisation to form a roughly triangular structure.
In the eighth sternite coremata are variably present in lower trifines,
but in higher trifines there is a trend towards loss of lateral rods, and,
just posterior to the anterior margin, occurrence of a transverse band of
long, hairlike setae.
Larval
morphology may provide a means of testing these indications of
relationship within the trifines; it is interesting to note that the only
published attempt to order the characteristics of both tropical and
temperate larvae, possible in India (Gardner, 1946-1948), led to an
arrangement that was very much at odds with the Hampsonian classification
then accepted (Kitching, 1984; 191). Subsequent work on larvae, reviewed
by Kitching, has tended to identify the trifines as a unit but has varied
widely in recognition of groupings within them.
Sugi
(1987) included members of the previously quadrifine Belciana Walker
complex of genera in the Acronictinae on the basis of larval features. The
relationship of the more plesiomorphic trifines with such quadrifine
genera requires further investigation.
Host-plant
specialisations and economic importance.
It
is generally true that herbaceous-feeding larvae are predominant in the
higher trifines and Heliothinae and Stiriinae, exceptions being mainly in
the Hadeninae and Cuculliinae, whereas in the more plesiomorphic trifines
arboreal feeding is predominant.
Within
the higher trifines there are three major groupings of grassfeeders which
include very many serious pests of cereal crops and pastures, both
tropical and temperate. In the Hadeninae there is the diverse Mythimna group,
and in the Apameini the complex that includes Apamea and both
temperate and tropical stem-boring groups; these are discussed in more
detail later. In both cases the ovipositor lobes are distinctively
modified to enable eggs to be inserted within the leaf sheath, though the
modification is very different in each group. The third group of
grass-feeders is found in the genus Spodoptera Guenee along with a
number of dicotyledonous feeders, mostly polyphagous but with a few rather
specialist taxa. Unlike the first two groups, there are no strong
indications that the graminaceous taxa form a natural assemblage (I.J.
Kitching, pers. comm.).
Most
of the other herbaceous-feeding genera found in Borneo are polyphagous,
exceptions being Actinotia Hubner on Hypericum (Guttiferae)
and Condica Walker on Compositae.
The
genus Callopistria Hubner is unusual in being restricted to ferns
as host-plants, a restriction seen also amongst the trifines in the
African hadenine genus Nyodes Laporte and the Old World tropical
and subtropical genus Appana Moore that occurs in Peninsular
Malaysia and Sulawesi but has not been recorded from Borneo.
Amongst
the arboreal feeders there are more specialist genera. In the Acronictinae
the genera Craniophora Snellen, Thalatha Walker and Thalathoides
Gen. n. all feed on the family Oleaceae. Agaristinae often show
a strong preference for Vitaceae. Dipterygina Sugi is restricted to
Callicarpa (Verbenaceae), and Sasunaga Moore and allied
genera specialise in the Rhamnaceae. Tiliaceae, Sterculiaceae and
Malvaceae are favoured by Chasmina Walker and possibly Dyrzela Walker.
Prometopus species may be conifer feeders.
A
most interesting specialisation is shown by the genus Mudaria Moore
where the larvae are borers in fruits of Bombacaceae, attacking durian and
kapok, and thus being of economic importance. This genus is a possible
sister-taxon to Chasmina, and so the combined grouping is
specialist on Malvales; Malvaceae and Bombacaceae have been treated as a
single family in the past.
Most
species of economic importance are found amongst the herbaceous feeders.
Those attacking Gramineae have already been mentioned, but the genus Spodoptera
also includes a number of highly polyphagous species that attack
vegetable crops, a species that is used for control of water weeds in
Thailand, and a rather bizarre indirect pest of fisheries in Fiji!
The
Noctuinae contain a number of cutworm genera that include pests in temperate regions. In the tropics their species tend to be montane but
could become more serious pests if there were an expansion of cultivation
of temperate vegetation at high altitudes. Agrotis Ochsenheimer
species are of particular importance in this respect.
The
Bornean Heliothinae number only two but both are known pests, attacking
the seeds and fruits of a number of crops such as maize, solanaceous
fruits, pulses, citrus and cucurbits.
The
majority of pests in the Hadeninae is in the genus Mythimna as
discussed above, but the polyphagous larvae of Tiracola Moore
species have also been recorded as defoliating a large number of plants of
economic importance.
The
Amphipyrinae include Spodoptera and the complex of graminaceous
stem-borers already referred to. The latter are far less diverse than in
Africa, perhaps reflecting the greater extent of natural grasslands in
Africa. The genus Athetis Hubner contains a number of generalist
herbaceous feeders that are often common in agricultural ecosystems. Condica
Walker, a specialist genus on Compositae, contains pest species that
attack safflower in India and are frequently encountered where weedy
compositae are common.
The
non-pest species found in abundance in agricultural systems feeding on
weeds may be of importance both for weed control and as reservoirs for
populations of non-specialist parasitoids and other natural enemies of
pests.
Ecology
and geography.
Trifine
noctuid species in the Oriental tropics fall into three main categories:species
of lowland rainforest; species of early successional and agricultural systems;
montane species (Holloway, Robinson & Tuck, in press).
Most
of the arboreal feeding 'lower trifines' fall into the first category. The
genera are, with a few exceptions such as Craniophora Snellen, entirely
tropical, mostly found only in the Indo-Australian tropics and a few restricted
to the Oriental tropics (e.g. Eulepa Walker) or most diverse there (Dyrzela
Walker, Mudaria Moore, Bagada Walker).
The
open habitat species of the lowlands are more cosmopolitan, occurring in the
Neotropics also, such as Spodoptera, Condica, Tiracola, Athetis and Callopistria
Hubner. The last is unusual in its fern-feeding habit and includes denizens
of the forest habitats as well. Most of these genera extend into warm temperate
areas, some, such as Athet is, strongly so. Many species migrate towards
higher latitudes at times.
The
Heliothinae are most diverse in semi-arid habitats from the tropics to
Mediterranean latitudes. The hadenine genus Mythimna has taxa
characteristic of both lowland open habitats and montane ones, and is diverse
also at temperate latitudes. However, the graminaceous stem-borers in the
Amphipyrinae appear to segregate into distinct tropical and temperate complexes,
the latter perhaps allied to the Apamea group of genera that includes
more general feeders (leaf, stem and root) on grasses. A few members of the
tropical Sesamia Guenee complex extend into southern Europe.
The
montane species are drawn mainly from genera diverse in temperate latitudes,
particularly the eastern Himalayas, and extend through the mountains of the
tropics often to south temperate latitudes. All noctuine genera are of this
category, as is Phlogophora Treitschke of the Apamemi, though this genus
may have its greatest richness within the tropics and subtropics. Most of the
'higher trifines' fall into this category though some, such as Apospasta Fletcher,
Euplexidia Hampson and Xenotrachea Sugi, are virtually restricted
to mountains in the tropics and subtropics.
Bornean
endemism is highest at the specific level in the montane category, including one
genus, Bornolis Gen. n., in the Hadeninae and several species found only
in the higher zones of G. Kinabalu. Endemism is moderate in the lowland forest
category, with many purely Sundanian species, and absent from the open habitat
category where species widespread in the Indo-Australian tropics predominate,
many extending also to Africa.
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