The
hypothesis that arthropod natural enemies can cause the extinction of
target
and non-target arthropods has been widely accepted despite a lack of
plausible
scientific evidence supporting extinction claims (Lynch and Thomas
2000; Lynch
et al. 2001). In the environmental and ecological sciences unverified
statements can reduce scientific credibility and have adverse
consequences on
garnering public support - both emotional and financial - for proposed
future
research. Such an undesirable effect is particularly pertinent for
programs
investigating the benefits and risks of biological control, especially
when the
risk of extinction, an irreversible ecological calamity, forms the
central
tenet of debate.
Deliberate
introductions into new areas of novel organisms such as biological
control
agents by its very nature entail some level of risk. Risk in this
instance, is
the uncertainty that damage to non-target organisms could be caused by
introduced natural enemies. Risk assessment estimates how much damage
can
result from an event involving the agent and risk management seeks to
determine
the acceptability of collateral damage the agent causes and devises
measures to
mitigate it (Lonsdale et al. 2001). Evaluation of techniques for
assessing risk
to non-target organisms posed by natural enemies being considered for
use in
biological control programs has received much research attention
(Lonsdale et
al., 2001) and interest in this area is continuing to grow rapidly,
especially
for arthropod biological control agents (Hopper 2001; Van Driesche and
Reardon
2004).
Perceived
risk associated with biological control projects can be amplified by
invoking
uncertainty that is associated with the project or practice in question
(Pidgeon et al. 2003). In the case of classical biological control,
risk to the
ecosystem receiving a novel exotic natural enemy pertains to
unpredictable,
unintended, and disruptive trophic perturbations that could be
manifested once
an exotic natural enemy permanently establishes in the receiving area
(Louda
and Stiling 2004). Such unintended consequences, should they occur, can
be used
to disparage the science underlying risk assessment in biological
control because
the environmental insult, should it occur is irreversible, and the
outcomes
should have been predictable and avoided if the science underlying risk
assessment is solid (Stiling and Simberloff 2000).
Extinction
is the most easily understood of all ecological phenomena and species
imperilment figures prominently in daily news and lay publications.
Extinction
events are unflattering commentaries about human stewardship of
ecosystems,
especially when deliberate actions with the aim of improving ecosystem
health,
such as management of invasive species with natural enemies, can be
correlated
with extinction events. Moral indignation about extinction is
particularly high
when attractive, or rare and endangered organisms or habitat have been
extirpated by deliberately introduced biological control agents.
One of
the most famous and "best documented cases of extinction" in
biological control is the extirpation of the pestiferous levuana moth, Levuana
iridescens Bethune-Baker (Lepidoptera: Zygaenidae) in Fiji, by the deliberately
introduced
parasitic fly, Bessa
(= Ptychomyia) remota
(Aldrich)
(Diptera: Tachinidae), from Malaya
(Howarth,
1991; 2001; New 2005). Levuana iridescens is only known from Fiji, and the last authentic specimen
of this
attractive "endemic" monotypic zygaenid genus was apparently
collected in Fiji
in 1929 (Howarth, 1991). Bessa remota has also been assumed to
have
caused the extinction of another endemic Fijian zygaenid, Heteropan
dolensDruce (Lepidoptera: Zygaenidae) (Howarth 1991, 2001; Robinson 1975;
New
2005).
Recently, this untested hypothesis, that an exotic natural enemy, B.
remota,
is responsible for the extinction of L. iridescens has been
challenged
(Kuris 2003; Sands 1997), but a larger part of this story has been
overlooked and
deserves attention. The remainder of this article provides additional
historical background on the "Levuana Campaign" not covered by the
Tothill et al. (1930) treatise, further challenges the assertion by
Howarth
(1991, 2001) that extinction of L. iridescens and H. dolens
has
occurred, and presents an update on recent museum, library, and field
surveys
for L. iridescens in Fiji.
Levuana
iridescens
was first recorded as a serious coconut pest around 1877 from a single
island, Viti Levu, in the Fijian
archipelago, a collection of
approximately 300 islands. Earlier records on coconut production from
1846 and
1860 do not indicate a severe and widespread malady affecting palms
(Simmonds,
1924). On Viti Levu, the only
location this
moth is known from, outbreaks of this moth were frequent and devastated
coconut
palms as moth larvae trenched undersides of leaves that often led
to
defoliation and palm mortality. As a consequence, copra production
(i.e., dried
coconut meat from which coconut oil is extracted) was severely affected
on Viti
Levu and coconut production was unprofitable and indigenous Fijian
culture,
which relied on the coconut for food, water, fiber, medicinal products,
fuel,
and building materials was adversely affected (Tothill et al., 1930).
Since its
first detection, L. iridescens was restricted to Viti Levu for approximately 40 years before it
began expanding its
range in 1916 to close offshore islands where conditions favored pest
establishment and proliferation.
The
highly restricted geographic range of L. iridescens was
considered a
"fact contrary to the usual position with regard to the endemic fauna
of Fiji"
(Simmonds, 1924). Scientists devising management schemes for L.
iridescens
concluded that the pest was not endemic to Fiji and was an exotic
invader
(Simmonds, 1921a; 1924). This conclusion was arrived at because L.
iridescens exhibited frequent outbreaks, was expanding its
geographic
range, and lacked specialized parasitoids associated with eggs, larvae,
or
pupae. These facts were recognized as very peculiar aspects of this
pest's
ecology when compared to other zygaenid species in their native range
which
outbreak infrequently, don't exhibit range expansion, and have diverse
suites
of associated natural enemies (Simmonds, 1924; Simmonds 1930a; Tothill
et al.,
1930). This circumstantial evidence did not, however, prove
conclusively that L.
iridescens was not native to Fiji, but did strongly
suggest the
moth had originated elsewhere and immigrated to the islands (Tothill et
al.,
1930). Unless L. iridescens is found
outside of Fiji
the tautology of this endemicity argument is difficult to conclusively
resolve.
To curb
the spread and impact of L. iridescens in Fiji and limit the threat
to other
coconut growing nations in the South Pacific the "Levuana Campaign"
was initiated in 1925 after a ₤5,000 reward failed to conjure a magical
solution to the problem. The leader of the campaign, J.D. Tothill, and
his two
associates T.H.C. Taylor and R.W. Paine were given a two year
contract
to
resolve the problem. Tothill viewed biological control as the only
feasible and
sustainable option available for permanently suppressing L.
iridescens.
Tothill et al. (1930) located and imported a tachinid fly, B. remota,
from Malaya where it controlled
another palm
defoiliating zygaenind, Artona
catoxantha.
Within six months of
release
of this fly from quarantine in August-September 1925, L. iridescens
populations had been reduced to almost non-detectable levels on Viti
Levu,
although persistent outbreaks continued on two small off shore islands
(Nukulau
and Makuluva) in the Rewa River Delta (Tothill et al., 1930). The last
specimen
of L. iridescens was apparently
collected in 1929 and is now assumed to be extinct because of B. remota (Howarth 2001).
Kuris
(2003) recently reviewed Tothill et al.'s (1930) treatise on the
classical
biological control of L. iridescens in Fiji with B. remota
from the
perspective of an invasion biologist. Kuris (2003) concluded that it
was highly
probable that L. iridescens was exotic to Fiji and that it was
unlikely that
natural enemies, in particular, B. remota, had caused the
extinction of L.
iridescens. Kuris's (2003) analysis supports earlier statements and
conclusions reached by Sands (1997) regarding the exotic origin and
extinction
of L. iridescens. Interestingly, a much larger part of the L. iridescens story has been overlooked.
Biological control was the last control option turned to after other
management
strategies had failed.
The Pre-1925 Management
Strategies for Levuana iridescens in Fiji
Cultural Control Strategies.
Cultural controls are
techniques that are developed from crop management or mechanical
practices that
can be readily manipulated to disadvantage pest population growth while
having
no adverse effect on crop health. Cultural control practices can
include the use
of plant varieties resistant to pest attack, soil amendments to improve
plant
health and vigor, the removal of alternate food sources the pest
utilizes, or
the use of traps to capture the target pest thereby reducing its
prevalence in
a localized area.
Oviri coconuts from Tahiti
were tested for resistance to feeding by L.
iridescens larvae. The astringent properties of this coconut
variety were
presumed to act as potential deterrents to herbivory and lack of
obvious insect
attack on coconuts in Tahiti provided
anecdotal field evidence suggesting that Oviri coconuts may be
unpalatable to
phytophagous insects (Simmonds 1920). Importation of Oviri coconuts
into Fiji
and subsequent feeding trials assessing palatability to emergent and
half-grown
L. iridescens larvae were inconclusive leading to the decision
that high
yielding resistant coconut varieties were not likely to be found easily
(Simmonds 1921a).
To reduce the debilitating
impact of L. iridescens outbreaks on palm growth, practices
designed to
promote plant vigor to enable infested palms to grow through
defoliation events
were promoted. Outreach programs encouraged plantation managers to
control
weeds, thin overcrowded plantations, use soil amendments, and to drain
swampy
ground (Tothill 1926). There are no data indicating the success of
these
suggested practices, or the extent to which they were employed for L.
iridescens control.
Light traps set at night
were assessed for their ability to attract adult L. iridescens.
Since
this moth is a day-flying insect, powerful acetylene lamps set over
pans of
kerosene mixed with water failed to attract moths at night (Knowles
1919).
Adult moths had been observed feeding at a variety of different flowers
including Lantana camara L.,
coconut, mango (Mangifera indica L.),
ginger (Zingiber spp.), mile-a-minute
(Polygonum
perfoliatum L.), and Tournefortia
argenta (Simmonds, 1925; Tothill et
al., 1930). Oddly, phenol and tar also had alluring properties
(Simmonds 1925).
Knowles (1919) speculated that if attractive volatile additives could
be
identified and isolated they could be used increase the attractiveness
of traps
to adult moths thereby enhancing the utility of this method of control.
There
is no published research assessing the feasibility of using traps for
monitoring L. iridescens populations, determining pest
phenology, or
implementation for localized control efforts.
Vulu
is the thatch or
fiber matting that connects the bases of coconut fronds. Levuana
iridescens larvae preferentially pupate in vulu. During Levuana
outbreaks, densities of pupating
larvae in vulu could become so great that cocoons would be spun over
the top of
existing cocoons rending emergence impossible for larvae in lower
strata
(Tothill et al., 1930). Manual removal of vulu as a pest suppression
tactic was
considered, but quickly abandoned due to the intensive amount of labor
required, and the difficulty of quickly ascending and descending tall
coconut palms.
Additionally, vulu removal destroyed habitat used by beneficial
arthropods such
as spiders that preyed upon pests (Knowles 1909).
In addition to coconut, L.
iridescens larvae feed on several other palm species, including Actinophloeus
macarthuri, Areca catechu (betel nut), Elueis
guineensis,
Guilelma speciosa, Livistona chinensis and L. speciosa,
Oreodoxaregia and O. oleracea (royal palms),
Sabal
palmetto, Sagus vitiensis (native sago palm), and Veitchia
joannis (niu sawa). During severe outbreaks, high densities of L.
iridescens would "spill over" onto less preferred hosts and eggs
and feeding larvae would be found on Artocarpus incisa (breadfruit),
bananas, reeds, sugar cane, and unidentified orchids (Tothill et al.,
1930; Simmonds
1925). "Drastic steps" such as the removal of food sources "to
starve out" L. iridescens were considered necessary in
combination
with burning and arsenical sprays to eradicate L. iridescens on
recently
invaded islands that lay offshore from Viti Levu (Simmonds 1922). A
similar
project proposed for Viti Levu would
have
eradicated all preferred hosts, in particular, coconuts and royal
palms. The
enormity of the project, the cost, and the uncertainty of eliminating
every
host plant led to the abandonment of this strategy at an early stage of
planning (Simmonds 1922; 1924).
In 1924, sea ports at
Suva, Levuka (all coconuts within 0.5 miles of this wharf were
destroyed), and
Lautoka were designated as inspection ports under the Diseases of
Plants
Ordinance (1913) and inter-island cutters were required to stop for
inspection
before moving from infested zones to non-infested zones (Tothill et al.
1930).
A tripartite cooperative involving growers, The Native Department, and
the
Government oversaw the inspection process. Vessels without special
exemptions
(some passenger, plantation owned, and freight boats were not legally
required
to stop) were subjected to inspection at one of the three ports and
were
awarded an Inspection Certificate and entry records were gazetted.
Vessel
inspections were voluntarily overseen by growers who had the authority
to
destroy all "objectionable and dangerous material" on boats moving
between islands (Tothill 1925a). Objectionable and dangerous material
of
primary concern was the movement of vulu between islands. Vulu, the
fibrous
material that grows at the base of coconut palm fronds, was regularly
harvested
and used as packing material, for wrapping perishable (e.g., taro roots
and
medicines) and fragile items, and enclosing letters (Tothill 1925a).
Vulu is
the preferred pupation site for L. iridescens larvae, and pupae
on vulu
can survive without sustenance for up to nine days making human
mediated long
distance transport of this life stage plausible (Tothill 1925a). The
inspection
system remained in place until 1928, "by which time Levuana moth had
been
reduced to a condition of impotency" by B. remota (Tothill et
al.
1930).
The need to quickly
control outbreaks of L. iridescens and for eradication of
incipient
populations of this pest as it expanded its range to islands
surrounding Viti Levu prompted
investigation of insecticides as a
control strategy. Efficacy of stomach poisons applied as foliar sprays
mixed
with seawater were assessed over the period 1909 - 1925. Insecticides
were
evaluated with seawater as the carrier because seawater is more readily
available than freshwater in Fiji
(Knowles 1909) and coconuts have a high tolerance to being drenched
with
seawater (Tothill et al. 1930). One lb of arsenic boiled with soda and
mixed
with 400 gallons of sea water, starch (as a sticker), and whiting (for
coloration) readily killed L. iridescens larvae (Knowles 1919).
Alternatively, 1.5 lbs of either lead or calcium arsenate mixed with 40
gallons
of seawater killed larvae within 5-10 days, and provided control for up
to two
months (Tothill 1925b). Approximately 12-24 months suppression was
achieved
with 2.5 lbs of dry lead arsenate mixed with 40 imperial gallons of
seawater when
applied to the undersides of coconut leaves. Paris green was unsuitable
because
of phytotoxicity and poor adhesion to coconut leaves (Tothill et al.
1930).
Application
of sprays to tall palms involved either the use of a power driven
pump
or the
erection of scaffolding around each palm to be treated by hand. A major
shortcoming associated with power application of wet sprays to tall
coconut
palms was the enormity of wasted spray to provide adequate coverage of
infested
coconut crowns. Costs associated with the employment of spray crews
(Knowles
1919) and scaffold erection and movement were prohibitively expensive
for hand
applications that treated palm crowns at close range (Knowles 1919).
Small
coconut palms were successfully hand-treated for L. iridescens
with
kerosene emulsions or resin washes (Froggatt 1914) and applications of
30 oz of
lead arsenate in 25 gallons of water applied at a rate of 4 gallons per
palm
with applications repeated at 5 week intervals also controlled larvae
on small
palms (Jepson 1915).
A rapid
reaction spray rig was custom developed for deployment against
incipient L.
iridescens populations on previously uninfested islands. This spray
rig
consisted of a sea-going barge with a motorized Fitz-Henry Guptill
solid stream
sprayer attached to its deck. A galvanized iron structure was built to
cover
the pump to protect both it and the crew from adverse weather and
excessive sun
exposure. The barge was towed by a launch along coastlines and spray
hoses up
to 0.5 miles long could be dragged into plantations needing treatment.
The
barge had ready access to seawater for mixing with poisons and beach
access
overcame difficulties of getting spray equipment into areas that lacked
roads
(Tothill 1925c). Trees 60-80 feet tall could be treated when weather
conditions
were appropriate and coconuts in close proximity to beaches and within
drag
line distance could be treated with this spray rig. The rapid
reactionary
capability of the floating spray rig was never tested as B. remota
rendered obsolete the need for insecticidal controls and treatment of
new
infestations on previously uninfested islands (Tothill et al. 1930).
Fumigation
of infested coconut plantations was also investigated. Sulfur mixed
with tar was burned over dry coconut leaves. This resulted in a thick
smoke
that would waft through infested plantations. Unless L. iridescens
larvae were actually scorched by the flames they suffered no mortality.
Clouds
of smoke in plantations were never dense enough to suffocate adult
moths, but
did succeed in agitating adult moths thereby encouraging flight and
dispersal
(Knowles 1919).
Levuana
iridescens was not considered native to Fiji
and its home range was presumed to lie to the north-west of Fiji
(Tothill et al., 1930). The
assumption for this geographic area of origin was that from 1802
onwards a
vigorous trade in sandalwood was routed from Cochin China through Fiji and the New Hebrides (i.e., Vanuatu) to areas east of Fiji.
From 1864 onwards, extensive
recruitment of labor for Fijian plantations from the Solomons and Vanuatu
occurred and this was considered another possible area from which L.
iridescens may have originated (Simmonds, 1924).Extensive foreign exploration by Simmonds
(1924) for approximately nine months (June 14 1922 - February 11 1924)
of
coconut palms and native palms such as sago, was conducted throughout New Guinea, Vanuatu,
Bismarcks,
and
Solomons. Specifically, Simmonds (1924) searched the northwest coast of
New Guinea, New Britain,
Witu, New Ireland, Bouganville, Shortlands, Russell Group, New Georgea,
Gela,
Ysabel, Guadacanal, Malaita, Manning Straits, Banks Group, Epi, Santos, Malakula, Pau Uma, Aoba, Penticoste, Sandwich and Tanna. This search failed to locate
L.
iridescens (Simmonds, 1924). Concurrently, A.M. Lea of the AdelaideMuseum
(Australia) surveyed
northern Queensland, Thursday Island
group,
and MagenticIsland. Lea's
efforts in 1924 also
failed to locate L. iridescens (Despeissis, 1925).
Consequently, L. iridescens is only known from Fiji.
Lea then
focused efforts in the Malay archipelago
where
he was assisted by G.H. Corbett, B.A.R. Gater, and S. Leefmans in the
search
for another zygaenid, Artona catoxantha, that exhibited
periodic
outbreaks resulting in defoliated palms reminiscent of damage caused by
L.
iridescens. Artona catoxantha was known to have suite of
natural
enemies that effectively regulated its population growth. It was
speculated
that some of these natural enemies should they be located may attack L.
iridescens as larvae of these two moths exhibited similar host
plant
associations, biology, ecology, and feeding behavior. Attempts by Lea
and
others to successfully ship live A. catoxantha parasitoids from
the
Federated Malay States to Fiji
prior to 1925 failed. In 1925, H.W. Simmonds was stationed in Kuala
Lumpur to
await outbreaks of A. catoxantha and if possible to
serendipitously
coordinate shipments of parasitoids collected from unpredictable
outbreaks
located somewhere in the Federated Malay States with infrequent
(approximately1-2
per year) sea-going freighters leaving this area enroute to Fiji.
Airplanes
were unavailable and the cost of chartering a naval or merchant vessel
for the
4,000 mile journey was prohibitive (Tothill et al. 1930). T.H.C. Taylor
was
dispatched by Tothill in 1925 to re-explore areas of New Guinea and then to push onto Cochin China. During this sojourn Taylor
stopped to visit Simmonds and this trip coincided with an A.
catoxantha
outbreak at Batu Gajah, 175 km north of Kuala Lumpur.
Parasitized
and unparasitized larvae (20,000 in total) were collected, caged on 85
potted
palms, transported 300 miles by train to Singapore where the cargo
was
loaded on the Clan Mackay for Surabaya Java on July 10, 1925. The
cargo was
transferred to Clan Matheson on July 12, 1925 and this ship arrived
in SuvaFiji
on August 3, 1925
with 315 live adult B. remota - 25 days after leaving Batu
Gajah
(Tothill et al., 1930). The suitability of L. iridescens as a
host was
unknown until the parasitoids arrived in Fiji and were presented
with L.
iridescens larvae in quarantine. In quarantine, adult flies
immediately
parasitized L. iridescens and fly larvae developed successfully
on L.
iridescens. Hyperparasitoids were removed from the L.
iridescens colony. By January 1926, 32,621 flies had been
successfully reared on L. iridescens and liberated. Complete
control of L.
iridescens was achieved approximately six months after releases of B.
remota commenced (Tothill et al., 1930) and is cited as a
premier
example
of classical biological control (Caltagirone 1981).
Inspection
of the Koronivia Research Station Insect Collection and Library Records
for Levuana
iridescens
Howarth's (1991; 2001)
claim that L. iridescens was extinct by 1929, but may have
persisted
until the 1950's and that the endemic H. dolens is extinct in Fiji
(Robinson 1975) was investigated by searching library accessible
literature
records and Fijian insect collections. In October 2002 and 2004, the
author
examined the insect collection at the Koronivia Research Station near Suva on Viti
Levu, Fiji,
for L.
iridescens and H. dolens. The Koronivia collection has 14
specimens
of adult L. iridescens, 8 specimens have collection data, the
remaining
6 are unlabeled. There are two L .iridescens cocoon samples on
vulu, one
is a single cocoon and the other is a mass of approximately 20 cocoons.
One
sample of larval L. iridescens trenching on the underside of a
coconut
leaf approximately 5 cm x 1.3 cm in size with around eight trenches has
been
preserved. The trenched leaf was collected in Serea, Viti Levu, April 13, 1939, the collector is not
named. The most recently lodged
specimens of adult L. iridescens were collected in December
1953, at
Taulevu (due west of Vunindawa) on Viti Levu.
Larvae were also collected from this L. iridescens outbreak in
Taulevu
that affected 100 coconut palms. The larvae were not located in the
Koronivia
collection. The most recently deposited specimens of Heteropan
dolens
are two adults collected from Taulevu in 1963. Detailed
collection data
for L.
iridescens and H. dolens are provided. In October
2004, a
large number of unlabeled Schmidt Boxes and Cornell Drawers were
inspected in
the Koronivia Collection for “undiscovered” L.
iridescens and B. remota
specimens. The search yielded six additional L. iridescens,
and one cocoon sample. All of this “new” material
was unlabeled so collection date and locality are unknown. Two of the
best
unlabeled adult L.
iridescens
specimens were returned to the EntomologyMuseum at the University of California
at Riverside for long-term curation. The overall condition of the
specimens in the Koronivia
Collection is extremely bad and further deterioration will occur
without
immediate efforts aimed at preservation.
Published
outbreak records for L. iridescens
post 1925 housed in library collections were searched for in the using
Entomology Abstracts. Accessible citations that could be located were
used to
construct a
map documenting the location and year of the published
outbreak. The last published journal record was 1942 (17 years
post-release of B. remota) and the final mention in
the
literature of L. iridescens being
observed on Viti Levu was 1956 (31
years
post-release) (Paine 1994).
MSH and DPA Sands (CSIRO
Indooroopilly, Australia)
attempted to locate L. iridescens on Viti Levu over the period October 29 2002 -
November 6 2002
in
southeastern Viti Levu around
Vunindawa,
Colo-i-Suva, and Laucala Point. The search for larvae and adult moths
followed
two concurrent avenues: (1) visual inspection of palm fronds for larvae
and
coconut flowers for adult moths; (2) broadcast distribution of "wanted
posters" with colored images of L. iridescens adults,
larvae, and
trenched leaves to village residents, and (3) sweep netting flowers
(e.g., lantana) within coconut plantations. The poster images were
taken from
the
Tothill et al. (1930) treatise and $100 (US) bounty was offered for
the
successful capture of any life stage of L. iridescens. The
poster
campaign was unsuccessful; no Lepidoptera were turned in for
identification.
Tothill
et el. (1930) state clearly that visitors intending to witness L.
iridescens
damage to coconuts post-release of B. remota should visit two
islands in
the Rewa River Delta, Nukulau and
Makuluva. Bessa remota had
failed to
provide consistent control of L. iridescens on these small
isolated
islands and it was assumed that a lack of secondary hosts for B.
remota
to sustain itself during periods of low L. iridescens density
was the
major cause for this lack of persistent suppression (Tothill et al.
1930). A
similar situation with respect to secondary hosts and primary pest
suppression
currently exists on Cape Cod, Massachusetts U.S.A. Brown tail moth, Euproctis chrysorrhoea(Lepidpotera: Lymantridae) a serious forestry
pest, is
successfully suppressed by the tachinid C.
concinnata in more interior areas but E.
chrysorrhoea is unregulated in areas of Cape Cod where secondary
hosts are
unavailable to maintain high populations of C.
concinnata (J. Elkinton pers. comm. 2004).
Attempts
by MSH and DPAS to gain access to Nukulau and Makuluva by
motor boat were
thwarted due to a heavy military presence and successful interception
on the beach
of Nukulau. Both
islands have been
converted to prison camps to house militants responsible for the
attempted May 19
2000 coup d’etat
lead by Fijian Nationalist George
Speight and
public access is prohibited.
Further, the floral diversity of these two islands appears to have
increased
from Tothill et al.'s (1930) time. From the sea, visual observation
suggested
that the remnants of old coconut plantations were suffering from lack
of human
management as thick understoreys were evident. These prevailing
conditions
would most likely create habitat that would favor increased
lepidopteran
biodiversity, which may be conducive to sustaining B. remota
populations
leading to permanent suppression of L. iridescens on small off
shore
islands.
During an
outbreak, L. iridescens exhibits a clear attack sequence. It
preferentially attacks the tallest coconut palms in a highly localized
area.
Once these palms are defoliated, surrounding palms are then attacked
until the
lowest growing palms are infested last (Knowles 1919). Based on this
description of the outbreak ecology of L. iridescens, and the
fact that
severe and prolonged outbreaks no longer occur, it is most likely that
this
insect inhabits the tallest palm trees in areas that support small
populations.
Consequently, visual searches for L. iridescens larvae on small
immature
coconut palms in southeastern Viti Levu
were
unsuccessful in 2002.
With this
attack sequence in mind, aerial
malaise traps were deployed
at Serea,
Taulevu, Vunindawa,
and TogaIsland near
Nausori on
the Rewa River Delta over the period October 5 – 31 2004. Traps were
suspended
on ropes 20-25m above the ground between adjacent coconut palms and
immediately
under the palm crown. Traps were lowered on a rope pulley system and
collection
bottles with 95% ethanol were checked every 3-4 days for L.
iridescens,H. dolens,
and B. remota over a 4 week period.
None of the target species were collected.
Visual
searches of palm fronds for L. iridescens
larvae were greatly hindered by feeding damage caused by larvae of
another
frond trenching lepidopteran, the coconut flat moth, Agonoxena
argaula
Meyrick (Agonoxenidae).
This pest causes damage to
undersides of palm fronds identical to L.
iridescens. In direct contrast to L. iridescens, A.
argaula
larvae spin silk roofs over the open tops of trenches they inhabit.
Abandoned
trenches lack silk coverings and are impossible to distinguish from
those made
by L. iridescens larvae. Additionally, A. argaula
larvae drop to
the ground to pupate and they do not utilize vulu as a pupation site. Agonoxena
argaula was present in Fiji
during the "Levuana Campaign" but was apparently insignificant
(Simmonds 1921b; Tothill et al. 1930). Population densities of A.
argaula
may have increased substantially following the successful biological
control of
L. iridescens as competition for undersides of palm fronds would
have
been greatly diminished. The high population densities of A. argaula
and
the common occurrence of severe feeding damage on palms would indicate
that at
the time surveys for L. iridescens
were conducted, coconut flat moth was not being efficiently regulated
by
natural enemies.
The creditability of
Howarth's (1991; 2001) assertion that biological control of L.
iridescens
with B. remota in Fiji
is one of the "best documented cases of extinction" has been strongly
challenged by invasion biologists (Kuris 2003) and biological control
specialists (Sands 1997). Data supporting Howarth's claims that natural
enemies
have driven L. iridescens to extinction are non-existent or at
best must
be considered weak as no comprehensive and prolonged campaigns to
search for
this zygaenid have been undertaken to verify the continued presence of L.
iridescens in Fiji.
Unfortunately, the published extinction assumption of L. iridescens
and H.
dolens by B. remota has largely been accepted as fact (New
2005)
despite a lack of confirmatory evidence (Lynch et al 2001), museum
records to
the contrary, and published reports of persistent L.
iridescens
outbreaks up to 1956. Post 1956, research by entomologists
employed by
Imperial Bureau of Entomology (a.k.a. Imperial Commonwealth
International
Institute of Entomology) to service tropical countries in the BritishColonialTerritories
in the South
Pacific began to wane and research on Fijian coconut problems
diminished. By
1966, the post-war PacificIsland projects were ended and research
teams
returned to the United
Kingdom (Paine 1994). The reduced
presence
of skilled entomological observers working on coconuts (a crop of
declining
economic value) in Fiji
most likely accounts for the cessation of reports of L.
iridescens outbreaks and also the lack of observations on B. remota which has not been seen since
the last observation of L. iridescens
in 1956.
The
endemicity of L. iridescens to Fiji
is unresolved but has been vigorously questioned by Sands (1997) and
Kuris
(2003). If L. iridescens is native to
Fiji why did
persistent
outbreaks begin on Viti Levu around
1877? It
is possible that new varieties of coconuts that were being grown in
large
plantations and the associated habitat modification allowed L.
iridescens to completely escape any
regulatory effect of it’s suite of endemic natural enemies. Further,
this
creation of natural enemy free space via agricultural practices
inexplicably
extended to encompass a number of native Fijian palm species and other
unrelated crop plants (e.g., bananas and bread fruit). This natural
enemy free
space was initially restricted exclusively to Viti
Levu
before undetermined factors facilitated its extension onto nearby
islands in
1916. This scenario while interesting, is implausible and makes it more
likely
that L. iridescens is exotic to Fiji
as it exhibited persistent population outbreaks and continued to spread
into
nearby and previously uninfested islands. Today, these phenomena are
recognized
to represent scenarios typical of invasive species infiltrating new
areas.
The claim
that H. dolens is extinct in Fiji
and B. remota is responsible (Howarth
2001; New 2005; Robinson 1975) is particularly worrisome. There are no
published field or laboratory data that H.
dolens is attacked by B. remota
(Tothill et al. 1930), that larvae are suitable hosts for B.
remota on which to complete development, or that this fly
forages in habitat or on host plants used by this zygaenid. Further, H. dolens is known to exist on other PacificIslands
(e.g., Aneityum Island,
Vanuatu
[Robinson 1975]).
Unverified extinction claims in the literature have undoubtedly
amplified the
social perception of risk when conservation biologists and ecologists
suggest
extinction of non-target species by biological control agents is well
documented and L. iridescens is used
as the example (Howarth 1991; 2001).
It is
very difficult to prove that the relatively recent absence of a species
is due
to its extinction. Zygaenids that are well regulated by natural enemies
are
known to exhibit long lag periods between outbreaks and this is a
clearly known
facet of their ecology. For example, Artona
chorista was presumed to have gone extinct until an outbreak 100
years
after its initial description occurred in cardamom plantations in Sikkim
(Tarmann 2005).
A robust
approach would be to compile available data that a species is absent
and then
assess whether the combined weight of that evidence is sufficient to
assume
that extinction has occurred. This type of analysis is advocated by the
Committee on Recently Extinct Organisms (CREO 2004; Holloway 2005) and
editors
of peer reviewed articles should insist that these standards be reached
prior
to publishing statements that species extinctions have occurred. To
substantiate or refute the extinction of L.
iridescens by B. remota within
the framework suggested by CREO, a comprehensive multi-year search for L.
iridescens in Fiji should be conducted, preferably between August
and
December (this time of year was when outbreaks were most severe) and
efforts should
be concentrated in the southeastern corner of Viti Levu in the area
circumscribed by Serea, Taulevu, Vunindawa, Colo-i-Suva and Laucala
Point (see
Map). The tallest coconut palms in these areas should form the foci
of
searches.
Indirect
evidence for the existence of L. iridescens could come from the
discovery of pupal
cases on vulu whose silk chemistry properties are
identical
to those of cocoons in the Koronivia Collection. Two subsamples of L. iridescens cocoons from the Koronivia
Collection have been deposited in the EntomologyMuseum at the University of California Riverside. Very small
pieces from both cocoon
samples were removed from masses and subjected to analyses to determine
the
“protein fingerprint” of the silk. The results
of the analyses
indicated very little difference in the amino acid profiles for both
samples
indicating that they are most likely from the same species. These
profiles
could be used to compare “fingerprints” from silk cocoons collected
from vulu
in Fiji
to determine if they belong to L.
iridescens. Silk amino acid profiles are often very specific to
particular
species (C. Hayashi pers. comm. 2005) and this forensic analysis could
provide
strong indirect evidence for the continued existence of L.
iridescens in Fjij.
Direct
evidence of the presence of L. iridescens would be the capture
of adult
moths or larvae.
Aerial malaise traps should be hung between the
tallest palms
at canopy level in search areas to intercept adult moths flying to feed
on
coconut flowers, or seeking oviposition sites, or mates. Fogging of
palm
canopies with insecticides to knock down foliage feeders may result in
the
collection of adult or larval L. iridescens, but persistent
maritime
breezes will make this strategy very difficult (T. Irwin pers. comm.
2004).
Surveys may best be conducted after cyclones have hit the islands
because of
the disruptive effect major storms have on biological control agents
thereby
allowing pest species to temporarily escape natural enemy regulation
(Paine 1931;
1994). Confirmation of the existence of L.
iridescens should be followed with an intensive effort to live trap
adult
moths, especially females, to develop colonies.
Tothill
et al. (1930) speculated that pheromones played a major role in mate
location
by male L. iridescens. Isolation and
identification of a sex pheromone would enable the development of
pheromone
traps that could be deployed in island groups to the west of Fiji,
the presumed historical home
range of L. iridescens. Use of
pheromone traps would allow the efficient sampling of low density L. iridescens populations and would be
an important tool in delineating the geographic range of this moth
outside of Viti Levu. Pheromone traps
are used routinely for the
monitoring of western grapeleaf skeletonizer, Harrisina
metallica Stretch (= brillans
Barnes and McDunnough) (tribe = Procridini), a pestiferous zygaenid of
grapes
in the U.S.A.
(Soderstrom et al. 1985). Blends of pheromone constituents with known
attractiveness to H. metallica could
be deployed in Fiji
in anticipation of eliciting partial responses (cross attraction) from
male L. iridescens. However, L.
iridescens (tribe Artonini) may not
respond to procridin pheromone blends (Gerhard Tarmann pers. comm.
2004).
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the non-target impact and spread of B.
remota in the Fijian islands needs research attention. The best
approach to
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(Memmott
2000) in a manner similar to studies conducted in Hawaii to determine
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