Pest Management Guidelines |
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Progress Towards Pest Management in Litchi | ||
By: Vincent P. Jones, Carrie H. M. Tome, Christopher J. Robb
Department of Entomology, University of Hawaii at Manoa
Honolulu, HI 96822
This paper will discuss the progress made towards the development
of an integrated pest management program (IPM) for insect control
on litchi. It will briefly discuss what IPM is, then focus on
research progress made in the last year.
Tables and figures referred to in this document are unavailable
at this time.
What is pest management and what sort of information is
required?
The textbook definition is "the intelligent selection and
use of pest control actions that ensure favorable economic,
ecological, and sociological consequences". For our
purposes, pest management is preventing economic damage to the
crop the best way possible considering as many factors as
possible. We are not trying to just suppress one insect's
population, but look at all the pests population levels and how
they affect the health of the crop. You could conceivably apply
pesticides every day and control your pests, but it is
economically unfeasible and ecologically it would destroy all
your natural enemies. In addition, your neighbor would probably
turn you in to the DOA. We are trying to set up a pest management
program that works and is sustainable over time.
There are several pieces of information required for an IPM
program. First, what are the pests and natural enemies present in
the crop? For fruit crops, when does the female attack the fruit?
It doesn't pay to protect your fruit when there are no insects
present, or when the fruit isn't susceptible to the insect.
Another important piece of information is the differences in
damage between cultivars and locations. This information gives
you an indication of what sort of damage levels you can expect
under certain situations. Along this same line of thought, we
also need to have some measure of the population level of the
pest and the natural enemies, so we can look and see if the
problem is getting worse or better. You don't want to be applying
pesticides if the population is getting better on its own, only
when it is getting worse. You also need some sort of information
on optimal timing of control measures. We are trying to put on
the pesticide only when it is required, and before the population
comes out, not after half of it is out and the damage is already
done. If you put on the pesticide too late, all you're getting is
revenge.
Where is the pest when it is not attacking the fruit? In litchi
this is critical because oriental fruit fly is a major problem
that we have seen this past year, and it does not complete
development in litchi except very infrequently. Many eggs are
inserted into the fruit, but do not complete development. This
means that the population which is damaging the fruit is coming
from outside the orchard. Because of this, it is important to
know where the pests are when they are not in your orchard.
You need to know the effect of control measures on the natural
enemies as well as on the pests. You don't want to put on a
pesticide which controls your main pest but which kills off the
natural enemies which suppress other pests. This is the sort of
information you need before you can make up a pest management
program.
Progress on Litchi IPM
I was contacted by the tree fruit growers to investigate this
problem on litchi after the harvest was already done (in 1991),
and it was felt the damage was primarily from Cryptophlebia,
which is litchi fruit moth (Cryptophlebia ombrodelta - known as
macadamia nut borer in
Australia) and the koa seed worm (Cryptophlebia illepida). So the
objectives of the study, was first to confirm the identity of
Cryptophlebia spp. attacking litchi, and secondly, to estimate
what percent crop loss there was from this particular insect. We
also wanted to determine the period in time that the fruit was
susceptible to feeding by Cryptophlebia, and lastly to survey
natural enemies and pests which may be upset in the pesticide
applications we use.
PEST BIOLOGY
Cryptophlebia spp.
The two species of Cryptophlebia found in the islands have
similar life histories. The koa seed worm, C. illepida, is
endemic to the Hawaiian islands and was first reported in 1919 on
macadamia. It has 18 host plants listed of which macadamia,
litchi, and mango are the main economically important hosts.
Litchi fruit moth is an accidental import from Australia first
reported in 1958 with most of the same host plants. The two
species look very similar and have basically the same biology.
The physical differences between them are that the litchi fruit
moth is a bit larger and more robust, and there is a small
difference in coloration. Both are found in about equal numbers
on litchi, while on macadamia we find about 85 percent koa seed
worm and 15 percent litchi fruit moth. The larval stage has
off-white skin and dark little platelets on the back with hairs
coming out, and a black or dark brown head capsule. Damage seen
on litchi is frass or fecal pellets sticking out of the fruit
that is generally dry, and if you cut open the fruit, you will
find damage and larvae inside the fruit.
Oriental Fruit Fly
Damage to litchi by fruit fly became evident late in the season.
The fruit flies seen in the orchard were all Bactrocera dorsalis
(Hendel), the oriental fruit fly (OFF). The damage is caused by
the female fly during the act of egg deposition (oviposition).
The female fly uses the ovipositor at the tip of her abdomen to
insert the eggs through the skin of the fruit. The wound is
frequently frothy and causes the skin to turn brown around the
hole. In a large proportion of the cases, OFF eggs can be seen in
the hole or next to it from the outside with a 10x hand lens.
When the skin is peeled from the flesh, the inside has a large
brown circular mark centered on the oviposition hole. The eggs
are often on the surface of the flesh, but can also be found
inserted several mm deep into the flesh. Eggs are generally
deposited in a batch of more than 10 eggs. Fruit deterioration is
hastened by bacteria and/or fungi introduced during the act of
egg deposition.
Fruit were held to determine the species of fruit fly and the
ability of the fly to complete development in litchi. None of the
infested fruit yielded adult fruit flies. In conversations with
Dr. Jack Armstrong, USDA Fruit Fly Research Lab Hilo, he
indicated that only oriental fruit fly has been seen in their
studies and that litchi is a very poor host. Fruit flies can
complete development in litchi according to his studies, but the
survival rate is extremely low. In our collections we found
second and early third instar larvae. This suggests that litchi
does not harbor resident populations of OFF; they must disperse
into the orchard from alternate hosts.
MATERIALS AND METHODS
Study sites were set up at five different locations: two in Kona
near Captain Cook, one on Oahu near Mililani and two on Kauai,
one near Kapaa and the other near Princeville. At all sites, we
placed pheromone traps, which are synthetic sex lures from the
females moths, so that we can collect male moths to determine
population changes over time. The pheromone traps work for both
koa seedworm and litchi fruit moth. These traps were changed at
two week intervals before the end of May 1992, and at
approximately one week intervals after this period until harvest.
We have collected fruit from different cultivars when possible at
each location each time the pheromone traps were changed. The
cultivar types and locations are listed in Table 1.
At each location, we tried to collect a minimum of 75 fruit per
cultivar per week. This was done by randomly selecting 3-4 trees
of a given cultivar and selecting 25 fruit per tree. The samples
were shipped to Oahu and fruit size, fruit color, presence of
Cryptophlebia eggs or larvae, and fruit fly damage was recorded
from each fruit. Because it is not possible to distinguish eggs
of the two Cryptophlebia species, egg deposition is recorded only
as Cryptophlebia spp. rather than as each species separately.
Over all five sites and four cultivars, more than 8,000 fruit
were examined for this study. Damage is reported as all samples
and the last 2 weeks before harvest. The all sample estimates may
be misleading at certain sites because the data were not taken
for all cultivars over the entire season. The last two weeks
prior to harvest are a good indicator of what the grower finds at
harvest time.
RESULTS
Cryptophlebia Species Identity
The litchi fruit moth and the koa seedworm have both been
collected at all sites in the pheromone traps. In Kona, the
litchi fruit moth population density was approximately 60% lower
than the koa seed worm population density throughout the study
period. On Kauai, the trends were reversed with litchi fruit moth
population levels being higher. On Oahu, the population levels of
both moths are extremely low compared to both Kona and Kauai.
Cultivar Differences
The percentage of fruits found with Cryptophlebia eggs varied
markedly within a location and between cultivars (Table 2). At
the first site on Kauai, there were marked differences between
the percentage of fruits with Cryptophlebia eggs present. The
cultivar Kwai May-Pink had the highest percentage of fruits with
eggs, followed by Kaimana, Kwai Mi and Groff. The Kwai May-Pink
sampled at this location were in a different block that the other
three cultivars and to some extent the differences in levels may
reflect a higher population density in that particular block.
However, high egg deposition was also observed on Kwai May-Pink
at the first Kona site, suggesting that this is a cultivar
specific trait. Egg deposition at the second Kauai site on Kwai
Mi and the first Kona site on Kaimana were also high, while that
observed on Kaimana at the second Kona site and Kwai Mi and Groff
at the Oahu site were quite low.
Table 2. % fruit with eggs from Cryptophlebia spp. present at
five different locations.
Table 3. % Fruit Damage to Litchi from Cryptophlebia spp. at five
different locations.
Damage from Cryptophlebia did not necessarily follow the egg
laying pattern (Table 3). In particular, there was a high
proportion of fruits with eggs at the second Kauai site and at
the first Kona site, but damage on the Kwai Mi and Kaimana
varieties was less then 2.5% and on the Kwai May-Pink
approximately 6.67%. This points out that there is a tremendous
amount of Cryptophlebia egg mortality occurring on litchi and
mere presence of eggs is not a good indicator of damage with will
be observed. Instead, the number of eggs laid is a better
indicator of potential damage if all conditions are favorable for
Cryptophlebia population growth.
Time Fruit are Susceptible
Adult female Cryptophlebia moths have been shown to lay eggs
primarily on macadamia nuts that are greater than 20 mm in
diameter. We found that also occurs on litchi (Fig. 1). On the
cultivar Kwai Mi, Å 5% of the eggs were laid on fruit that were
less than or equal to 20 mm in diameter. Also, the size-egg
deposition relationship remained fairly constant between the
different sites (Fig. 1). When looking at the cultivars Kwai
May-Pink and Kaimana, it appeared that the moths were laying a
greater percentage of eggs on progressively smaller fruit , but
even so, at 20 mm, only 8.8 and 3.8% of the fruit had
Cryptophlebia eggs present (not enough eggs were laid on the
cultivar Groff at either site to determine the relationship for
that cultivar accurately). From these data, protection of the
fruit before they are 20 mm long appears to have little benefit
regardless of the cultivar grown.
Fig. 1. Cryptophlebia oviposition on various fruit sizes on 3
different cultivars at 3 different sites.
Groff litchi appears to be relatively non-susceptible to KSW
(Tables 2 & 3). This may be related to the relatively small
size of this cultivar (peak average size Å 26 mm) and the
relatively short period between which it achieves 20 mm in length
and harvest begins. At the location on Kauai, the average fruit
length was over 20 mm for approximately 21 days, but harvest was
occurring during the last two weeks of this period. Studies
performed in temperature cabinets have shown that Å 8 days is
required for egg hatch at 20°C. Therefore, the window in time
during which the female moth lays eggs and harvest is quite
narrow. For damage to occur on this cultivar in significant
amounts before harvest, females would have to be at high
population levels just when the litchi are slightly less than 20
mm in diameter. Prompt harvest assures that damage will not be
excessive.
The cultivars Kwai May-Pink and Kwai Mi both exhibited a rapid
fruit growth and an extended period where they were over 20 mm
long. At the Kona site, the Kwai May-Pink was greater than 20 mm
in diameter for a period of 55 days, and at the Kauai locations
for 49 and 50 days. The Kaimana litchi at Kona was greater than
20 mm for at least 46 days, and on Kauai for at least 44 days.
The longer period in time between 20 mm in length and harvest
makes a close synchrony between the moth populations and fruit
size less important and consequently, the potential damage from
Cryptophlebia on these cultivars is greater.
Oriental fruit fly
Regardless of its ability to complete development in litchi, the
dispersal of OFF into the orchard and subsequent fruit damage is
an extreme problem for litchi growers (Table 4). Damage levels
were high on all the cultivars (at least at one of the sites),
except for Groff. The most extensive damage was found on the
cultivars Kwai Mi (Å 31% damage) and Kaimana (Å 28% damage) at
the second Kauai site and the first Kona site, respectively.
There is considerable variation in damage within a single
cultivar between sites. This probably reflects the fact that
because litchi is a poor host to build up OFF populations, most
of the damage must come from flies which migrate into the orchard
from surrounding vegetation. It is particularly interesting to
note that the Kaimana cultivar at the two Kona orchards were less
than 1000 yards away from each other, yet the damage levels were
Å 28% and 0.4%, respectively. The orchard with the lower damage
level had coffee interplanted with litchi and was not irrigated,
while the other field was a mixed cultivar block in the center of
a large tropical fruit orchard. The other interesting comparison
is the high damage level on Kwai Mi at the second Kauai site
compared the other two locations.
Table 4. Percentage Fruit Damage to Litchi from Oriental Fruit
Fly at five different locations.
Time of susceptibility to oriental fruit fly.
As with other crops (such as papaya), the period of fruit fly
susceptibility is closely tied to the state of fruit maturity.
Because we recorded the color of each fruit as green, 1/3 red,
2/3 red or full red, we were able to determine at which stage
most OFF damage occurred. The general trend for all cultivars was
that within a site, damage at the green stage was fairly low to
non-existent compared to the 2/3 red or full red color (Fig. 2).
The Kwai May-Pink cultivar showed an unusual amount of damage on
the 1/3 red stage, but this may be related to the difficulty in
judging the more yellowish color of this cultivar.
Fig. 2. % Fruit damage by oriental fruit fly on three different
cultivars and four different ripeness stages.
Damage at different heights from Cryptophlebia spp. and Oriental
fruit fly. At the second Kauai site, we were able to take some
samples from high in the canopy and compare the damage to that
observed in the
lower part of the canopy. For both species, the damage was
significantly higher at the lower elevation (Å 2 meters) vs. the
higher elevation (Å 7 meters) (Fig. 3). This means that the
success of a management program could be determined from samples
on the lower branches without fear that the top of the tree is
suffering high damage levels.
Fig. 3. Effect of height from ground on damage estimates for
oriental fruit fly and koa seedworm.
Does Oriental Fruit fly only attack fruit damaged by
Cryptophlebia spp.? One of the questions I was asked was do fruit
flies only attack fruits already damaged by litchi fruit moth?
The answer to this is clearly no. Damage on a number of the
cultivars is much higher from oriental fruit fly than it is from
litchi fruit moth. At two of the sites, one in Kona and one in
Kauai, there was enough litchi fruit moth and oriental fruit fly
damage that we were able to do statistical tests of the
association, and the two types of damage were completely
independent.
Other Insects and Mites Found on Litchi
There is a wide variety of insects found associated with litchi.
Their economic importance varies depending on cultivar, location,
orchard cultural practices and treatment history. This makes
predicting the pest status or the effect of pesticide
applications on non-target species associated with the crop
difficult and imprecise at best.
Of the 18 species observed, four are serious pests which must be
deal with on a regular basis, 3-4 have questionable pest status,
6 are natural enemies of pest species, and 3 are pollinators
(Table 5). To reduce damage from this complex requires a
management plan which reduces the pest species, but does not
eliminate the natural enemies or the pollinator spp.
There are several pests other than Cryptophlebia and oriental
fruit fly which are important. The most widespread pest is the
erinose mite which occurs on the leaves. I found this everywhere
I worked on litchi. If left to itself, high population levels can
develop and leaves are severely deformed.
Spider mites were another problem, particularly in the drier
parts of the islands. They caused a significant amount of leaf
bronzing, but nobody seemed to care that much; I didn't see any
leaf drop, the population seemed to drop off in the warm part of
the summer. They are something surely to be concerned about in
the future. The predator mites are another thing we have to be
concerned with in the sense that they prey on the spider mites
and the erinose mites and if we contemplate using pesticides on
litchi we have to make sure that the predator mites are not
destroyed or you are going to have perennial spider mite and
erinose mite problems.
MANAGEMENT
Cryptophlebia spp.
Populations of these two moths can be monitored using pheromone
traps which can be obtained from several commercial sources.
Trece, Inc. [(408)-758-0205, Salinas California] is the direct
supplier. The traps required are the pherocon 1CP and the lures
are for the oriental fruit moth (OFM). Locally, Brewer
Environmental may be able to special order the traps and lures.
Lures should be replaced at 3 week intervals and the bottoms of
the traps when they get dirty. The number of moths found in the
traps should be recorded at approximately weekly intervals to
determine if populations are increasing rapidly at a time when
the fruit are susceptible (0.7" in diameter or 18 mm
diameter).
Registration of carbaryl is being completed for control of
Cryptophlebia. Carbaryl is used in Australia for control of
Cryptophlebia and is quite efficacious. Based on our studies,
Cryptophlebia do not attack fruit less than about 18 mm in
diameter (0.7"). Sprays should not be applied before this
time regardless of the population density recorded in pheromone
traps. The cultivars Kwai Mi and Groff probably do not have to be
treated, but Kwai May Pink will probably require treatment to
prevent damage. Kaimana may also need to be protected, depending
on the population level in the orchard and the surrounding host
plants.
The use of mating disruption has been tried on Cryptophlebia spp.
on macadamia in Hawaii. Mating confusion involves using the
synthetic sex lure used in pheromone traps to saturate the entire
orchard. This is thought to reduce mating because it is difficult
for males to find female moths. The trials on macadamia were not
a success, although egg deposition was reduced by 50%,
significant damage still occurred. Work on this in the future
will probably intensify and improved application technology may
make this a viable option in the future.
Oriental Fruit Fly
Oriental fruit fly does not complete development to any
significant degree in the litchi orchard. They migrate in from
the outside and deposit eggs into the fruit, which rarely
complete development. However, the act of puncturing of the fruit
to lay the egg results in a oozing wound and the introduction of
microorganisms into the fruit, rendering it unsaleable.
Strategies for management of the insect therefore require that
the fly is prevented from moving into the orchard. Because only
female flies damage the fruit, all control measures should be
aimed at the females.
Traps for monitoring oriental fruit fly should be aimed at the
females. Current trapping using methyl eugenol as an attractant
are useless for pest management. First, they trap only males and
secondly, as stated above, they may have an attractive radius of
greater than 1 mile. Considering that most of the tropical fruit
orchards are rather small, and that if the traps are placed near
the edges, many of the flies trapped are not from your orchard,
but instead come from the surrounding region. For pest
management, you want a trap with a limited radius of attraction
so that you can see what's happening in your orchard. If you want
to know population levels outside the orchard, place a trap
outside the orchard. Traps which should work for fruit fly
attraction are yellow panels coated with tanglefoot (an adhesive)
and having an ammonia lure (available commercially from several
manufacturers). Alternatively, yellow balls approximately 8.5 cm
diameter coated with tanglefoot should provide information on the
changes in population levels if trap catch is recorded weekly.
Traps should be replaced when dirty or when the lure expires.
Carbaryl, which is being registered for Cryptophlebia spp. on
litchi, is not effective against oriental fruit fly, therefore
the registration of malathion and a partially hydrolyzed yeast
protein bait (Nulure) should be pursued. This combination is
generally considered to be the most effective control measure for
fruit flies, because the female flies require the protein source
for egg production. The malathion generally has a preharvest
interval of less than 3 days. For example, the Clean Crop
Malathion 8 aquamul has a preharvest interval of 2 days on mango,
passion fruit and guava, but on citrus it is 7 days. The downside
of this pesticide is that the residue is short-lived, lasting
less than 7 days under even the best conditions. However, its low
mammalian toxicity means that it would probably be easier to
register than other materials. It would be wise to register this
material on any tropical specialty fruit that will be sold fresh
market. If it is easier to register malathion without Nulure,
this should be pursued.
Because of the long period that some of the litchi cultivars are
susceptible, a material with a longer residue should be
investigated. However, a systemic material is not desirable,
because the flies do not complete development in the fruit
anyway. A contact insecticide is required. Candidate materials
all require the approval of the manufacturer for registration.
Before any material is used on a widespread basis, its effects on
natural enemies must be tested to prevent what is known as
"the pesticide treadmill". The pesticide treadmill is
when natural enemies for secondary pests are eliminated by
pesticide treatments for a particular pest and then treatment for
the other pests is required because their natural enemies are
gone. This leads to more and more pesticide use. We currently
have few pesticides registered, but all new materials should be
introduced with caution.
Other possibilities include any pesticide with a repellent
action. This would be particularly effective in litchi because
the oriental fruit fly population is primarily moving in from
outside the orchard. A neem product (Azatin«) is discussed below
and may be good for fruit fly control.
Bait buckets used by some growers only capture adult males.
Because males do not damage the crop, this is a
"revenge" tactic which costs money, but does nothing to
reduce damage. The idea behind the bait buckets is that by
trapping out all the males in an area, that females will not be
able to mate and lay fertile eggs. However, in litchi, the
females are migrating in from outside the orchard and have a
flight range of greater than 1 mile. All females may not be mated
upon entering the orchard, but it is almost certain that a large
proportion are. In studies on other crops where oriental fruit
fly can complete development, it is clear that greater than 99%
of the males in the area must be trapped out before any reduction
in fruit infestation levels are found. This sort of tactic must
be applied to a large area. Studies by the USDA fruit fly
laboratory have shown that a 63 hectare papaya field with a very
high density of bait buckets (or other dispensers) were not able
to reduce damage levels.
Malathion can now be used on the windbreak trees to reduce
immigration into the orchard (see the Hawaii Tree Fruit Journal
#2 for information). In high population levels, this may not be
very effective, but in areas with low population levels, spraying
the windbreak trees with malathion and Nulure (protein bait) will
provide some relief for growers.
When a pesticide is registered for fruit fly control, they should
not be applied until the fruit begin to color. While green, we
almost never saw any damage. The Kwai may pink cultivar, which is
somewhat yellowish, should be watched closely because it and hard
to determine exactly when it begins to change
Litchi Erinose Mite
This mite is easily controlled by sulfur, but sulfur is not
registered on litchi. Studies in Australia have shown that
erinose mite moves between trees by traveling on honeybees (and
probably large flies, etc.). Erinose mite can probably be
controlled using Safer's Insecticidal Soap, if the coverage is
good. Coverage is extremely important, because Safer's has no
appreciable residue and kills entirely by contact. A benefit of
using Safer's is that it is generally not toxic to predaceous
mites which help keep erinose mite populations regulated.
Future Candidate Pesticides. The industry should pursue the
registration of materials which may control pests not currently
found within the state. A good candidate is Azatin« which is an
extract of the neem tree, Azadaractica indica. This product now
has a very favorable registration category which allows
registration with very minimal testing - the industry must
request it and phytotoxicity tests must be run according to the
manufacturer. Azatin« has activity against whiteflies, thrips,
and lepidopterous larvae. It also acts as a repellent in some
trials and may therefore be a good candidate for helping reduce
oriental fruit fly damage. As with any pesticide, the effects on
natural enemies must be examined.
PRECAUTIONARY STATEMENT
Use pesticides safely. Follow the pesticide label. Consult with
the Cooperative Extension Service or the Hawai'i State Department
of Agriculture for authorized special local need registrations or
additional information. The user is responsible for the proper
use, application, storage, and disposal of pesticides.
DISCLAIMER
Reference to a company or product name does not imply approval or
recommendation of the product by the College of Tropical
Agriculture and Human Resources, Cooperative Extension Service,
University of Hawai'i, or the United States Department of
Agriculture and does not imply its approval to the exclusion of
other products that may be suitable. All matenals should be used
in accordance with label instructions or manufacturers'
directions.