Stenoma
catenifer,
the avocado seed moth, is a new world species that is thought to feed
exclusively on the fruit and seeds of plants in the family Lauraceae.
It has
been recorded feeding on fruit of avocados (Persea
americana) and the greenheart tree, Chlorocardium rodiei, an important
timber tree in Guyana
(Cervantes Peredo et al., 1999). Stenomer
catenifer is a well known avocado pest attacking fruit in Mexico, Guatemala,
Costa Rica, Panama, Bolivia,
Colombia, Peru, Ecuador,
Venezuela, and Brazil
(Acevedo
et al., 1972; Boscán de Martínez and Godoy, 1984).
Avocados in Guyana
are likely attacked as this moth has been recorded from fruit of
greenheart in
this country (Cervantes Peredo et al., 1999).
Levels of S. catenifer
infestation in avocados can be high. In some avocado growing regions of
Brazil
100% of the crop can be infested with S.
catenifer (Nava et al., 2005a), and in orchards that are sprayed
with broad
spectrum insecticides 7-11 times over the course of a
single
growing season up to 60% of fruit can be infested with larval S. catenifer (Nava et al., 2005b). Consequently,
this pest is considered to be one of the major impediments to
commercial
avocado production in Brazil
(Nava et al., 2005a,b). In Venezuela,
avocado fruit infestation with S.
catenifer larvae can be as high as 80% (Boscán de
Martínez and Godoy,
1982).
Eggs
and
Oviposition:Stenoma catenifer
eggs are small and oval in shape (on average eggs are 0.59 ±
0.04 mm long and
0.38 ± 0.2 mm wide) (Cervantes Peredo et al.,
1999). Eggs
are laid singly and are initially white or pale cream when first laid
and later
darken as they mature. Female moths oviposit at night with peak
oviposition
occurring within four hours of darkness in which time 80% of eggs are
laid
(Nava et al., 2005a). Stenoma catenifer females
tend to lay eggs on rough surfaces and in crevices such as the fruit
pedicel or
necrotic spots on fruit (Hohmann et al., 2003).
Oviposition studies in
cages
indicate that up to 68% of oviposited eggs can be laid on the branch to
which
the avocado fruit pedicel is attached (Hoddle unpublished data, 2007).
In the
laboratory, caged females can be induced to lay eggs on rough quilted
paper
towel as long as avocado fruit are provided as a stimulus to induce egg
laying
(Nava et al., 2005a).
Larvae: First instar larvae are pale cream to a very light
violet in color. As
larvae pass
through successive instars they become progressively more violet in
color. The
final fifth instar (up to 25 mm in length) is characterized by having
violet
dorsal coloration contrasting strikingly with a blue-turquoise colored
ventral
surface. When fifth instar larvae are ready to pupate the majority
(>95%)
will abandon the seed or fruit within which they are feeding, initiate
active
walking and climbing for approximately 12 hours, after which they will
enter a
quiescent period for another ~12 hours, often in a protected spot
(e.g., under
paper towel in the lab). During this quiescent period larvae will spin
a very lose and
fragile silk
tent within which they will pupate.
Pupae:
Pupae are “free” chrysalises that may be loosely attached
with fine weak silk strands to a substrate but can be easily dislodge
with
gentle prodding. In the field, S.
catenifer pupate in the soil at 0.5-2.0cm depth
after leaving the fruit they were feeding in (Boscán de
Martínez and Godoy, 1984). Young pupae are a striking turquoise
blue in color
and within 4-8 hrs of initial pupation this color becomes reddish-brown
as pupae
mature and melonize. Male and female pupae can be separated based on
the
presence of a small “suture” that divides abdominal segment 9 in the
males
(Cervantes Peredo et al., 1999). Some S. catenifer
larvae (<5%) will pupate within the seed in which they were feeding
(Hoddle
unpublished data).
Adults:Adults
moths are light tan color, and wings are
marked with numerous black spots. The most characteristic marking on
the
forewings is the easily observable “C” shape of spots as the distal end
of the
forewings. Adult females are about 15 mm in length (tip of head to tip
of
wings) when in the resting position with wings folded across the
dorsum. Wing
span for females with forewings fully spread is around 28-30 mm in
breadth.
Males tend to be slightly smaller (2-3 mm shorter) than females and are
similarly
colored (Hoddle unpublished data 2007).
During the day, the majority of adult S.
catenifer rest in dried leaf duff, weeds, and other litter in
avocado orchards and this behavior has been recorded in more natural
forest situations as well (Cervantes et al., 1999). Flight monitoring
of 45 laboratory-reared adult S.
catenifer into an avocado orchard at 2:00pm in the afternoon
revealed the following: (1) Adults (n=15) released individually at 1.5
meters on open ground in full sun all flew immediately into orchard
weeds and dried avocado leaves and hid. (2) Adults (n=15) released
individually at 1.5 meters immediately under the shade of an avocado
canopy all flew directly to the ground and similarly hid amongst and
under dried avocado leaves or in soil cracks. (3) Adults (n=15)
released individually at ~3.5 meters of height within the canopy of
avocado trees all flew directly to the ground to seek refuge. The
distance measured for adult Stenoma
flight upon release from plastic vials ranged from 3 to 12 meters.
Table 1.
Mean
developmental times for eggs, larvae, pupae and egg to adult for Stenoma catenifer reared on Breda avocados (from Nava
et al., 2005c).
Feeding
Damage, Oviposition Preferences, Influence of Altitude on Distribution,
and Avocado Cultivar
Preferences
The major economic damage caused by S.
catenifer larvae is feeding inside fruit and subsequent damage
to seeds and fruit pulp. Infested fruit hanging in trees with obvious S.
catenifer damage are characterized by whitish exudates (a
mixture of seven carbon sugars composed primarily of
perseitol) that run
down
the side of the fruit, accumulations of frass kick outs at the end of
feeding
galleries, and easily observable holes in the side of fruit. Opened
fruit may
show frass accumulation in the void that forms around the seed as the
pulp
separates from the seed as the fruit matures, seeds with feeding holes,
or
seeds completely destroyed by larval feeding can be found inside opened
fruit. Complete seed destruction
can
occur in small fruit that harbor more than two S. catenifer
larvae. Surveys of Hass avocados collected from
commercial orchards in Guatemala have revealed that 1-2 larvae per seed
is the
most common level of infestation. However, it is not uncommon to find
the
occasional seed with 3-4 S. catenifer
larvae, and occasionally 7-8 larvae may be found feeding in one seed
(Hoddle
unpublished data 2007). In Brazil
>55% of avocado fruit that are attacked by S. catenifer are in the upper half
of the
tree
(Hohmann et al., 2003). Surveys of damaged Hass fruit in Guatemala
indicate that 8% of S. catenifer holes are in the top
1/3 of
the fruit, 38% are in the middle third, and 54% are found in the bottom
1/3 of
the fruit. Approximately 14% of fruit exhibit more than one S.
catenifer hole (Hoddle unpublished
data 2007).It is possible that fruit
infested with S. catenifer larvae
fruit may be prematurely aborted and will drop to the ground where
larvae
continue feeding in the seeds before emerging from fruit to pupate in
the soil.
In the laboratory, when given a choice between Hass avocados or
Criollos that are 85% mature, Stenoma
females will lay significantly more eggs, up to 2.69 times more eggs on
Hass fruit than Criollos. The reason for this preference is unknown,
but it is possible that ovipositing female Stenoma can distinguish between
fruit types of different qualities and preferentially lay more eggs on
higher quality fruit. Hass is well known for its high oil content, a
characteristic that makes this cultivar popular with humans. Stenoma may also prefer lipid rich
avocados as hosts for offspring. Alternatively, the rough bumpy texture
of Hass fruit in comparison to smoother skinned Criollos may be
attractive to ovipositing females. Oviposition studies in the
laboratory have demonstrated that Stenoma
prefers to lay on substrates that have a rough texture (Nava et al.,
2005a). Whatever the stimulus (oil content or rough skin), under
laboratory conditions it appears that Hass avocados are a preferred
variety for ovipositon by Stenoma females.
Surveys of Hass avocados in Guatemala support this suggestion
that Hass are a preferred cultivar as an average of 45% fruit in some
commercial orchards exhibit feeding damage by Stenoma larvae.
In Guatemala,
S. catenifer infestations of avocados
appear to be limited to altitudes below 5,200 feet. At higher altitudes
(>5,500 feet) S. catenifer is very
uncommon (possibly non-existent) and not readily detected in harvested
or
dropped fruit collected in Hass orchards or from criollo trees (Hoddle
unpublished data 2007).
Avocado varieties vary in their
susceptibility to S. catenifer (Ventura et al., 1999;
Hohmann, 2000). Attack rates may be as low as an average of 4.5% of
fruit in
Booth, intermediate in Fuerte at 23% and high in Rincon at 54% damage
(Hohmann
et al., 2000). Field observations in 2007 in Guatemala indicated that
Hass avocados are readily attacked by S.
catenifer, with damage averaging 45% from 600 randomly sampled
fruit that were examined on three different occassions (i.e., 200 fruit
examined per sampling event). The results of field surveys on Hass
avocados in Guatemala would suggest this cultivar is amongst varieties
highly preferred for attack by Stenoma.
In Brazil,
S. catenifer eggs are attacked by Trichogramma
sp. and Trichogrammatoidea sp. parasitoids and
up to ~60% of eggs can be parasitized. However, this level of attack is
not
high
enough to prevent economic damage (Hohmann et al., 2003). Larvae in Brazil
are
attacked by a variety of hymenopterous parasitoids which can cause up
to 30-40%
parasitism. Larval parasitoids recorded from S. catenifer
larvae include: Cotesia
(Apanteles) spp. Dolichogenidea sp., Hypomicrogaster
sp., Chelonus sp., and Hymenochaonia
sp. (all Hymenoptera: Braconidae)
(Nava et al., 2005b). Ichneumonids have also been recorded from S. catenifer larvae and include: Eudeleboea
sp., and Pristomerus sp. (Nava et al., 2005b).
In Guatemala, the dominant
larval
parasitoid attacking S. catenifer is
a gregarious Apanteles
sp. which can succcessfully parasitize
50-100% of larvae. Estimates of parasitism levels from surveys in
Guatemala are affected by
location, number and time samples were taken (Hoddle unpublished data
2007).
Young Apnateles sp. larvae
erupt out fifth instar S. catenifer
larvae and
about 4-8 hours after emergence the majority of larvae have spun silk
cocoons. The number of parasitoid larvae emerging from S. catenifer larvae ranges 2-27,
and averages 8-9 larvae per host. A small number of S.
catenifer larvae die in avocado seeds and
parasitoids pupate within larval feeding galleries within the avocado
seed. Adult parasitoids are black with orange coxae. The sex
ratio is around 53% male and 87% of adult parasitoids successfully
emerge from cocoons (Hoddle unpublished data 2007).
The second most important parasitoid
attacking S. catenifer in
Guatemala is a solitary braconid, Macrocentrus
sp. Adult parasitoids are dark yellow in color with brown markings.
This parasitoid causes third and fourth instar S. catenifer larvae to abandon
avocado fruit before fully maturing. A single pale colored parasitoid
larva emerges from hosts which have a contracted dehydrated appearance.
Macroncentrus larvae spin a
very distinctive beige colored and cigar shaped cocoon.
Terrestrial predators are likely to be important natural enemies of S. catenifer because mature S. catenifer larvae emerge from the
protection of avocado seeds to pupate in the soil and adult moths seek
refuge in leaf duff on the orchard floor during day light hours. One
very common ground predator encountered in Guatemalan avocado orchards
during the day and night was the lycosid spider Hogna sp. In laboratory trials,
this predator readily consumed larval, pupal, and adult S. catenifer. Spiders were still
alive 36 hrs post-feeding indicating that immature and adult S. catenifer life stages did not
have any adverse intoxicating effect on these predators.
Establishing and Maintaining a Stenoma catenifer Colony
Introduce adult moths into a cage (e.g., commercially available
bugdorms [see photo] are perfect rearing cages for adult S. catenifer) and supply adults
with 10% honeywater in a vial with cotton wick suspended from the roof
of the cage. Honeywater is a food source and should be changed
every 5 days as it begins to ferment. Provide clean avocado fruit to
stimulate oviposition. Fruit should be thoroughly washed and dried to
remove contaminants (e.g., dirt, predatory mites, scales, and mealy
bugs) before introducing into the cage. Female Stenoma will
oviposit on fruit,
pedicels, and branches attached to fruit. Female moths will also lay
eggs on
dimpled paper towels (Nava et al., 2005a) and clean avocado seeds that
are placed in the cage.
Every
7 days remove fruit, seeds, and paper towel from cage. Replace with new
fruit,
seeds, and paper towel. With the removed fruit, seeds, and paper towel
do the following
things:
1) Cut pedicel (leave about 1-1.5 cm of pedicel on the fruit. This will
reduce the rate at which fungus will grow into the fruit from the
exposed button) from fruit and place in a box with clean fresh avocado
seeds that have had the seed coat (testa) removed. Seed coat removal is
very easy. Crack open ripe, uninfested avocados that may be just
starting to show signs of mold/fungus growth. Remove the seed and clean
vigorously with paper towel. The coarse paper towel will remove the
seed coat. Seed coat removal has two advantages: (i) it reduces greatly
the likelihood of fungus growing on the seed, and (ii) very young Stenoma that hatch from eggs on the
pedicels and branches can more easily burrow into the clean seeds.
Place clean avocado seeds and avocado pedicels/branches that have Stenoma eggs in a ventilated sealed
container with two layers of paper towel. The eggs will hatch on the
avocado pedicel/branch and the young larvae will attack the seeds. At
this time remove paper towels and seeds from the oviposition cage as
these may have
eggs and place in a ventilated container with clean avocado seeds and
with two layers of paper towel (larvae will pupate between the layers
of paper towel). Larvae hatching from eggs on the paper towel will
burrow into the clean avocado seeds and commence feeding.
2) Remove the avocado fruit with eggs from the
oviposition cage and place in either a sealed ventilated container
or another cage. Leave the fruit undisturbed for about 2 - 2.5 weeks.
During this time the
Stenoma eggs will hatch and the young
larvae will burrow through the avocado pulp to the seed to start
feeding. After
2 - 2.5 weeks crack open the fruit, extract the seed, clean and place
in a
ventilated container with two layers of paper towel. The larvae will
continue to feed and develop within the cleaned seeds.
3) Every week get 40-50 avocado fruit to use for egg laying in the
oviposition cage (about 12 fruit in the cage). The unused fruit should
be opened when ripe and the seeds extracted and cleaned for feeding to
young caterpillars.
4) After 3-4 weeks the mature Stenoma
caterpillars will exit the seeds and begin vigorous walking in the
container for about 12 hrs. After this time the majority will hide
between the sheets of paper towel and will begin to pupate. After an
additional 12-24 hrs remove pupae from ventilated container and place
in the oviposition cage or seperate for use in experiments.
5) After about 10 days the pupae will finish development and the adult
moths will emerge into the oviposition cage. The adults will mate and
lay eggs in the cage and the cycle will repeat.
Acevedo,
E.,
Vasquez, J., and Sosa, C. 1972. Estudios sobre el barrendor del
heuso del
aguacate
Stenoma catenifer Walsingham
(Lepidoptera: Stenomidae). Agrociencia 9: 17-24.
Boscán
de
Martínez, N. and Godoy, F.J. 1982. Apanteles
sp. (Hymenoptera: Braconidae) parasito del
taladrador de fruto del aguacate Stenoma catenifer Walsingham (Leipidoptera:
Stenomidae) en Venezuela.
Agronomia Tropical 32: 319-321.
Boscán
de
Martínez, N. and Godoy, F.J. 1984. Observaciones preliminares
sobre la biologia
de Stenoma catenifer Walsingham (Lepidoptera: Stenomidae) taladrador del aguacate (Persea americana Mill.). Agronomia Tropical
34:
205-208.
Cervantes
Peredo, L., Lyall, C.H.C., and Brown, V.K. 1999. The stenomatine moth, Stenoma catenifer Walsingham: a
pre-dispersal seed predator of Greenheart (Chlorocardium rodiei
[Schomb.]
Rohwer, Richter and van der Werff) in Guyana. Journal of Natural
History
33: 531-542.
Garcia,
A.M.,
Villa, M.M., Gutiérrez, A.M. 1967. El aguacate: plagas and
enfermades. Fitofilo
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Hohmann,
C.L., Dos Santos,
W.J., Menegium, A.M. 2000. Avaliação de técnicas
de manejo para o controle de
broca-do-abacate, Stenoma catenifer
(Wals) (Lepidoptera: Oecophoridae). Rev. Bras. Frutic. Jaboticabal 22:
359-363.
Hohmann,
C.L., Meneguim, A.M., Andrade, E.A., Novaes, T.C., and Zandoná
C. 2003. The
avocado fruit borer Stenoma catenifer
(Wals.) (Lepidoptera: Elachistidae): egg and damage distribution and
parasitism. Revista Brasileria de Fruticultura 25: 432-435.
Nava
D.E.,
Parra, J.R.P., Diez-Rodríguez, Bento. J.M.S. 2005a.Oviposition
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Stenoma catenifer (Lepidoptera: Elachistidae): chemical and physical
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and diel pattern of egg laying. Annals of the Entomological Society of
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D.E., Parra, J.R.P., Costa, V.A., Guerra, T.M., and
Cônsoli, F.L. (2005b). Population dynamics of Stenoma
catenifer (Lepidoptera : Elachistidae) and related
larval parasitoids in Minas Gerais, Brazil. Florida
Entomologist 88: 441-446.
Nava D.E., de Lara Haddad, M., and Parra,
J.R.P. 2005c. Exigências térmicas, estimativa do
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Ventura, M.U.,
Destro, D.,
Lopes, E.C.A., and Montalván, R. 1999. Avocado moth
(Lepidoptera: Stenomidae)
damage in two avocado cultivars. Florida
Entomologist 82: 625-631.
Stenoma
catenifer,
the avocado seed moth, is a new world species that is thought to feed
exclusively on the fruit and seeds of plants in the family Lauraceae.
It has
been recorded feeding on fruit of avocados (Persea
