Download Main Points Moths (Lepidoptera) Brownheaded Leafrollers

Avocado Growers Manual
Pests
Pests
Main Points
• There are a range of insect, mite and mammalian
pests that attack avocados
• Leafroller caterpillars can cause severe damage
to an avocado crop and egg rafts on the fruit are a
quarantine problem
• Greenhouse thrips can cause severe
discolouration on fruit resulting in rejection for
export
• Sixspotted mite infestations can cause tree
defoliation reducing fruit size and yield
• To control pests some form of spray programme
is usually required
A range of insects, mites and mammalian pests are found
on avocados in New Zealand. Some of these insects and
mites are pests, while others are benign or beneficial. It
is important to be able to distinguish pests from nonpests in order to make effective management decisions.
The biology and symptoms of damage caused by the
main pests of avocado are described here, along with
some information about their most common natural
enemies.
Control of leafrollers currently depends on a programme
of suitable insecticide sprays on a calendar basis, or as
determined by results of leafroller scouting.
Brownheaded Leafrollers
Ctenopseustis obliquana (Walker) and Ctenopseustis
herana (Felder and Rogenhofer), Lepidoptera:
Tortricidae. These two species cannot be distinguished
by eye but produce different pheromones.
Damage
Damage by leafroller feeding causes scarring resulting
in fruit being rejected for export, and can also lead to
increased fruit drop. Egg rafts are a quarantine problem
on export fruit.
Larvae are found feeding on foliage throughout most of
the year, either within a leaf ‘roll’, or between two leaves
that have been woven together by silk webbing. In times
of new leaf growth, larvae can be found feeding in the
soft young tips of leaf shoots. Over the winter, when
there are not many young leaf shoots present larvae can
be found sheltering alongside the main vein on the
underside of mature leaves. Feeding sites are
characterised by the presence of silken webbing that is
produced by the larvae.
Moths (Lepidoptera)
Leafrollers (Lepidoptera: Tortricidae) are the most
important pests of avocados in New Zealand. These
include the native brownheaded leafrollers
Ctenopseustis obliquana and Ctenopseustis herana; the
native greenheaded leafrollers Planotortrix excessana
and Planotortrix octo; the native black-lyre leafroller
Cnephasia jactatana; and the introduced lightbrown
apple moth Epiphyas postvittana. In addition,
caterpillars of Stathmopoda spp. (Lepidoptera:
Gelechiidae) can sometimes be found damaging fruit.
The most important species on avocados are the
brownheaded leafrollers, which account for about 90%
of the caterpillars found on fruit. Occasionally larval
case moths are found feeding on avocado fruit but these
are only found very rarely.
Leaf roller larva damaging fruit
© Copyright NZ Avocado Growers Association
August 2001
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Pests
Avocado Growers Manual
Larvae feed on the surface of fruit, often at the stalk end
of young fruit, or between two touching fruit in a cluster
of mature fruit. When both mature and immature fruit
are present on the tree at the same time, larvae prefer
young fruitlets.
On unsprayed trees, up to 70% of the fruit can have
feeding damage especially when a high proportion of
fruit hangs in clusters where one caterpillar is able to
damage several fruit while remaining protected. In light
crops more fruit hangs singly and does not offer the
protected feeding sites of a large cluster and less fruit
are usually damaged.
Description
Adult moths have a characteristic ‘bell’ shape and are
approximately 8-15mm in length with a wing-span of
15-30mm. The wings are brown and tan and there is
considerable variation between individuals in the
patterning on the wings.
Life cycle
Females lay between 10 to 500 eggs over their lifetime.
Eggs are laid in groups referred to as egg rafts containing
10 to 50 eggs laid in an overlapping pattern on the upper
and lower surface of avocado leaves and also on fruit.
Leafroller egg rafts bear a superficial resemblance to
psocid (barklice) eggs. Psocids are not a pest as they
mostly feed on dry organic matter and fungi. However,
while individual psocid eggs are cylindrical in shape
and are laid adjacent to each other unlike leafroller eggs
that are flattened and oval in shape and are laid in an
overlapping pattern. Pscocid eggs are usually laid in
groups of eight or nine in a loose mass and are covered
with a fine webbing. There is no webbing on leafroller
egg rafts. Leafroller eggs take between 5 and 30 days to
hatch depending on temperature.
Piscod eggs
Newly hatched larvae are very small, measuring only
about 2mm in length. Leafroller caterpillars disperse
rapidly after hatching, by crawling and by transport on
wind currents by silken threads. Larvae moult five or
six times eventually reaching 15 to 20mm in length. After
the final larval stage, caterpillars form a pupa, often
within the final feeding site. Adult moths emerge from
the pupae after a variable length of time depending on
temperature.
Approximately three generations occur per year in
Avocado growing areas. These generations overlap so
that all life stages can be found throughout the year.
However, most damage to avocado fruit occurs between
fruit set and June.
Host Plants
Brownheaded leafrollers have an extremely broad host
range and more than 100 host plants have been recorded.
Host plants include a mix of native and introduced plants.
Natural enemies
Generalist predators that feed on various life stages of
brownheaded leafrollers include spiders, the predatory
wasp Ancistrocerus gazella, the predatory mite Anysistis
baccarum, and the common earwig Forficula
auricularia. Although these generalist predators can play
a role in population regulation, leafrollers only form a
part of their diet.
Leafroller egg mass (hatched)
Predatory mite (Anysistis baccarum)
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Avocado Growers Manual
Pests
Leafroller eggs are parasitised by Trichogrammatide
wasps that are less than 1mm in length and are adapted
to develop within leafroller eggs. The adult wasp lays a
single egg within each leafroller egg that hatches out
into a small grub that eats the contents of the leafroller
egg. Leafroller eggs that have been parasitised go black
after about 7 days.
T. brevifacies eggs on leafroller shoulder
Parasitised leafroller eggs
Leafroller caterpillars are attacked by a number of
parasitoids but the two most common are the wasp
Doligogenidia sp. and the fly Trigonospila brevifacies.
T. brevifacies pupal cases
Thrips (Thysanoptera)
Trigonospila brevifacies
The wasp Doligogenidea sp. lays eggs into young
leafroller caterpillars. The eggs hatch within the
caterpillar and the parasitoid larva eats the caterpillar
from the inside. It is not possible to see if a leafroller
larvae has been parasitised by Doligogenidea sp. The
parasitoid pupates outside the dead caterpillar enclosed
within a white silky case.
The fly T. brevifacies lays cream/white eggs on the
‘shoulder’ area of the caterpillar. After hatching the fly
larvae burrows inside the caterpillar eating the inside of
the larvae. The fly larvae then emerges from the dead
caterpillar and forms a brown pupal case, which often
has the old caterpillar ‘skin’ attached. Pupal cases of T.
brevifacies are similar in colour to leafroller pupae,
however they are much shorter and squatter.
© Copyright NZ Avocado Growers Association
Two kinds of thrips can be found on avocado trees the
damaging Greenhouse thrips and the harmless New
Zealand flower thrips. Greenhouse thrips is considerably
different in appearance to the New Zealand flower thrips
and the two should never be mistaken for the other.
Greenhouse thrips never infest flower parts of avocados.
The biology and life cycle of these two species of thrips
is very different.
Greenhouse thrips are usually controlled by broadspectrum insecticides used for leafrollers but if selective
products are used for leafroller control it may be
necessary to specifically target control measures against
greenhouse thrips. Good coverage is essential at the tops
of trees where thrips damage has often been noticeable
when ground spraying large trees. Helicopter spraying
should give a good result on large trees. Control of New
Zealand Flower thrips in avocados is not required.
Greenhouse thrips
Heliothrips haemorrhoidalis (Bouché). Greenhouse
thrips are found throughout the world. In New Zealand
they occur outdoors as far south as Nelson, and within
glasshouses in more southern regions.
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Avocado Growers Manual
last between 8 to 90 days. Pupae can be found sheltering
on the feeding surface. Pupation does not take place in
the ground.
Greenhouse thrips (Heliothrips haemorrhoidalis)
Damage
Feeding by both larval and adult greenhouse thrips
causes severe damage to avocado leaves and fruit. Thrips
damage the surface cells by causing a slivery-bronze
scarring that results in fruit being downgraded or even
rejected for export and in severe cases local market.
Adult thrips cause about six times as much damage as a
larvae, and a single adult feeding on a fruit over eight
weeks would cause sufficient damage for that fruit to be
rejected for export.
Greenhouse thrips larva
There are several thrips generations per year, and they
are active through autumn and into winter in warmer
districts and mild seasons. All stages of greenhouse thrips
can be found throughout the year in avocados and
populations often peak in autumn. Adult thrips do not
generally migrate onto new season fruit until late January
or February.
Host Plants
Greenhouse thrips has a very wide host range and has
been recorded on more than 40 types of plants. Host
plants include Acmena, Citrus, Camellia, Persimmon,
Kiwifruit, and Rhododendron.
Thrips damage on fruit
Description
The adult thrips are about 1.25mm long, narrow in shape
and black in colour, with a lighter central stripe formed
by the pale wings folded along the back. Greenhouse
thrips are relatively sedentary and are more often seen
crawling rather than flying.
Natural enemies
Several generalist predators have been recorded
attacking greenhouse thrips in New Zealand but these
have little effect on greenhouse thrips populations. A
specialist parasitoid, Thripobius semiluteus, has recently
been introduced to control greenhouse thrips. T.
semiluteus is a tiny wasp that lays its eggs within the
body of larval greenhouse thrips. The wasp larvae kill
the larval thrips before reaching pupal stage. At present
it is too early to determine the effect of T. semiluteus on
greenhouse thrips populations.
Life cycle
The adults are all female and lay eggs inside the plant
tissue. The egg development period depends on
temperature but ranges between 20 and 160 days. The
eggs hatch into wingless larvae that are transparent/
yellow in colour. The time spent as larvae can range
between 14 to 130 days depending on temperature.
Greenhouse thrips larvae carry globular faecal droplets
on the ends of their abdomen that fall onto the feeding
surface leaving very characteristic dark circular marks.
Greenhouse thrips has two non-feeding pupal stages that
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August 2001
Thripobius semiluteus attacking a thrips larva
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Avocado Growers Manual
Pests
Greenhouse thrips larvae killed by T. semiluteus
Oribatid mite
There is currently no recommended control programme
available for sixspotted mites.
New Zealand Flower Thrips
Thrips obscuratus (Crawf.)
Description
New Zealand Flower Thrips are native to New Zealand.
They are found throughout the year in flowers of native
and introduced plants. Adult females are usually dark
brown while adult males are a yellow colour. The thrips
are from 1 to 3mm in length with a lot of variation in
body size between different individuals. Two pairs of
long narrow wings are folded down the length of the
abdomen.
Sixspotted Mite
Eotetranychus sexmaculatus (Riley), Acarina:
Tetranychidae. Sixspotted mites were first recorded in
New Zealand in 1953, although they may have
previously been confused with two-spotted spider mite.
They are present in many countries including Australia,
China, Hawaii, India, Japan, Korea, and the USA.
Life cycle
Eggs are laid within plant tissue and hatch into pale
coloured, wingless larvae that pass though two moults
before becoming pre-pupae and then pupae. The nonfeeding pre-pupae and pupae stages have short wing
buds and are found on the ground beneath trees.
New Zealand Flower Thrips has been recorded in the
flowers of many plant species. Feeding by New Zealand
Flower Thrips on avocado flowers does not appear to
cause damage to fruit.
Mites
Mites can feed on plants, fungus or be predatory. A
number of different mites are found on avocados, most
of which do not feed on the plant. However, the plantfeeding sixspotted mite can be a serious problem,
especially in northern avocado growing regions. It is
important to be able to distinguish non-plant-feeding
mites such as oribatids, tydeids, and predatory mites
from sixspotted mites.
Six spotted mite (Eotetranychus sexmaculatus)
Damage
All life stages feed by sucking out the contents of plant
cells. Feeding occurs on the underside of the leaf,
adjacent to the main leaf vein, and appears as a purple
discolouration. The most serious effect of sixspotted
mites feeding is defoliation.
Oribatid mites, the hard, dark, “beetle mites”, are not
damaging to avocados or any other crop but can be a
significant quarantine problem. The predominant
species, Ingella bullager is native to New Zealand and
is also found on other crops, including kiwifruit, feijoas,
persimmons and citrus. Post-harvest treatments of
Pyrethrum are the most effective way of ensuring that
avocados are free of mites prior to export.
© Copyright NZ Avocado Growers Association
August 2001
Six spotted mite damage
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Avocado Growers Manual
Description
Adult sixspotted mites are about 0.3 mm in length and
are generally a light yellow colour with a number of
dark markings in the back and sides. Despite the name
there are not necessarily six spots visible and the number
and shape of the markings can vary considerably.
Life cycle
Adult females lay about 25-40 shiny white circular eggs
on the underside of leaves over 10-20 days. The eggs
take between 5 days to 3 weeks to hatch depending on
temperature. Once the eggs hatch the mites pass though
three immature stages before becoming adults.
Sixspotted mites can undergo very rapid population
increases in suitable conditions. Mites can be present in
orchards throughout the year but at present there is not
much known about the population dynamics of six
spotted mites. However, it appears that the cooler
conditions in autumn and spring are ideal for rapid
population growth and that high temperatures inhibit
sixspotted mite activity.
Armoured Scale Insects (Hemiptera)
Latania Scale and Greedy Scale
Hemiberlesia lataniae (Signoret) and Hemiberlesia
rapax (Comst.). These scale insects are found all over
the world. While greedy scale is present throughout the
North Island, it appears that the range of latania scale is
still expanding and is not yet present in all areas of the
Bay of Plenty. Armoured scale insects occur most
commonly on avocados in the Far North growing
regions.
Control is achieved by routine insecticide applications,
and if broad-spectrum materials are used for leafroller
control, these will also give some control of scale.
Damage
The presence of scale insects on fruit causes a cosmetic
defect. Occasionally the presence of a scale insect can
be associated with a small ‘dimple’ in the surface of the
fruit.
Host Plants
Sixspotted mites have been recorded on at least 40 types
of plants. Host plants listed in New Zealand include
kiwifruit, Robinia pseudoaccacia, fig, plum, and grapes.
Natural enemies
The natural predator populations of several species of
predatory mites and ladybirds usually effectively
controls Sixspotted mite populations. Predatory mites
include the whirly gig mite Anystis baccarum, the
stigmaeiid Agistemus longisetus and unidentified species
of Phytoseiid mites. Both adult and larval Stethorus sp.
ladybirds feed on eggs, and larval stages of mites.
Scale insects
Description
This group of scale insects are described as ‘armoured’
as they are basically a soft bodied insect protected by a
very hard ‘cap’ the so-called armour. The cap of mature
scale insects is round/convex and is a creamy/white
colour measuring about 2mm in diameter. The actual
body of the insect is a bright yellow ‘blob’, with very
little obvious structure. When scale insects die, they
remain attached to the plant, but the scale body becomes
brown and dried out.
Ladybird larva (Stethorus sp.)
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Life cycle
Mature female scale insects produce a young stage
known as ‘crawlers’ which are the only life-stage with
legs and capable of dispersal. Crawlers disperse by
crawling or are blown by wind currents. The crawler
eventually ‘settles’ on a plant where it attaches to the
plant and begins to secrete the waxy scale cap. Once
attached the scale insect is unable to move, and is
permanently fixed in one place for the rest of its life.
August 2001
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Avocado Growers Manual
Pests
The crawlers settle on all parts of the avocado tree
including wood, fruit and leaves. Once settled, the scale
insect passes through three developmental stages,
separated by a moult, before becoming mature.
Scale insects have 2 to 3 generations each year, but most
stages are present at any one time. It has been shown
that significant numbers of scale insects settled on mature
fruit over the flowering period in an orchard in the Far
North (Blank et al. 1994.) but the pattern of scale insect
settlement over the season for other districts is not
known. The options for controlling scale insects over
the blossom period are limited due to the risk of
insecticides causing bee toxicity.
Beetles/Weevils
Adults of several species of beetle (bronze beetle and
grass grub) and a weevil (Fullers Rose weevil) can
occasionally cause damage to foliage of avocado trees.
The grass grub, Costelytra zealandica, is a New Zealand
native insect. In late spring and early summer the adult
beetles emerge from the soil to mate and disperse. During
this period they feed voraciously at night on attractive
host plants and during the day they drop to the ground
and hide in the litter or surface soil. The bronze beetle
Eucolaspis brunnea is also a native insect. The beetle
is mostly active between October to January but are
present until Autumn. Fuller’s Rose Weevil,
Asynonychus cervinus, can be found feeding on avocado
foliage between December and April.
Host Plants
Armoured scale insects have a very wide host range,
occurring on many woody plants. They can be found on
many commercial horticultural crops, many commonly
used shelterbelt species, and some native plant species.
Natural enemies
There is little information available about the predation
of scale insects. In the 1990’s a predatory mite,
Hemiscarcoptes coccophagoous was released into New
Zealand, but at this stage its establishment and role in
controlling scale insect populations is unknown. There
are two very small parasitic wasps (Encarsia citrina and
Signiphora merceti) that have been recorded attacking
both greedy scale and latania scale.
Bronze beetle (Eucolaspis brunnea)
Minor Pests
These are usually controlled by the insecticide
programme to control other pests.
Mealybugs (Hemiptera: Pseudococcidae)
These are a minor pest of avocados, not usually
damaging the tree or the fruit, but occasionally occur as
a quarantine problem. The most common species is
Pseudococcus longispinus.
Fullers Rose Weevil (Asynonychus cervinus)
Mealy bug
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Mammalian Pests
Rabbits and Hares can damage newly planted trees,
while opossums and rats will damage fruit on the trees.
Physical barriers around young trees will prevent rabbit
and hare damage or a repellent based on thiram can be
used. Opossum or rat control is best achieved by baiting,
trapping and shooting.
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FURTHER READING
Avocado Pests and Disorders; ed Roger Broadley,
1991. Queensland Department of Primary Industries.
Blank, R., 1994. Latania Scale Establish on Avocados
During Pollination. The Orchardist, May; Psocid Eggs
Unwanted Passengers on Avocados. The Orchardist,
June, 1994.
Steven, D., 1990. Kiwifruit Science and Mangement;
Ian Warrington and Graham Weston. Chapter 13,
Entomology and Kiwifruit, pp 362-412.
Stevens, P., 2000. A review of spider mites on
avocados with particular reference to the sixspotted
spider mite Eotetranychus sexmaculatus (Riley).
Report for the New Zealand Avocado Industry
Council.
Stevens, P., Froud, K., and Jamieson, L., 2000.
Greenhouse thrips in avocados. AvoScene, March: 1316.
Stevens, P., Jamieson, L., and Cave, J., 2001.
Sixspotted mites on avocados. Report for the New
Zealand Avocado Industry Council. Also on the
website: http://www.nzavocado.co.nz/.
Stevens, P., McKenna, Cathy., and Steven, D., 1995.
Pest Management for Avocados in New Zealand.
Proceedings World Avocado Congress III. (pg 429432).
Web site: http://www.hortnet.co.nz
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