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Unit D: Controlling Pests and Diseases in the Orchard

Lesson 3: Identify and Control Insects of Fruits and Nuts

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Terms

• Eggs• Nymph• Adult• Instar• Imago• Larvae• Pupa

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I. Understanding the vocabulary used when describing insects will help when controlling insects in the orchard. Some common terms include:A. Most insects develop from eggs which contain

the developing nymph.B. Nymph is the name given to the young stages of

those insects which undergo a partial metamorphosis. The nymph is usually quite similar to the adult except that its wings are not fully developed. It normally feeds on the same kind of food as the adult.

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C. The adult is the mature form of the insect which has the ability to reproduce.

D. Instar is the stage in an insect's life history between any two moults. A newly-hatched insect which has not yet moulted is said to be a first-instar nymph or larva. The adult (imago) is the final instar.

E. Larvae is the name given to a young insect which is markedly different from the adult: caterpillars and fly maggots are good examples.

F. The 3rd stage in the life history of butterflies and other insects undergoing a complete metamorphosis during which the larval body is rebuilt into that of the adult insect is called a pupa. It is a non-feeding and usually inactive stage.

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II. There are a number of insects which can cause damage in a fruit and nut orchard. The most common insects and their control methods are covered below. This is not an all-inclusive list and other insects may occur in your area.

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A. Leopard moth (Zeuzera pyrina)1. Life cycle and description

a. oval and salmon to orange-yellow color about 1.5 mm long. Females will lay 400-600 eggs under the bark of trees.

b. Adults Leopard Moths have a furry white thorax with six black spots.i. The wings are heavily spotted and are about

35–60 mm long.ii. Females are larger,iii. The moth flies from June to September

depending on the location.c. Larvae will hatch in about 10 days after eggs are

laid. d. Soon after they will burrow into the nearest bud,

twig or branch crotch.

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e. They will enter the pith and grow to about 25 mm by the end of the first season.

f. In fall, larvae bore tunnels that slant upward, 50 mm or more below the bark surface, where they remain dormant over winter.

g. Larvae resume feeding the following summer, pass a second winter in dormancy, and begin pupation the second spring after the eggs hatch.

h. Pupation takes about 4 weeks. i. The pupal cases remain in the exit holes

and is one method of determining their existence in the orchard.

8Adult

Larvae

Eggs

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2. Damagea. The caterpillar feeds on the

fruit and nut trees. b. It can burrow inside the

branches and feed for up to two years where it will emerge and pupate under the bark.

c. The earliest signs of damage will be girdled or broken twigs.

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3. Controla. It is difficult to control this pest once it has

burrowed into the stems and branches. b. Controlling the adults before they lay eggs or

the caterpillars before they burrow into the stems and branches will ensure control in the next year.

c. The best control is birds, also remove any infected branches and destroy them by burning.

d. Insecticides can be used in the tunnels. e. Since females do not move far from where

they pupated to lay their eggs, space trees far enough so that the moths will not move to other trees.

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B. Apple aphid (Aphis pomi)1. Life cycle and description

a. Eggs are shiny black and oval shaped. b. They are generally found on smooth twigs

and water sprouts.c. The green-colored young, called nymphs,

begin to hatch from overwintered eggs as soon as shoot leaves are rapidly expanding. i. The nymph is about 1.5 mm long,

yellow-green to dark green and oval shaped, generally found on smooth branches or leaf undersides.

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d. The adult can be winged or wingless about 3 mm long and bright green. i. The adult will commonly be

found on the underside of leaves.

e. The first aphids produced in the spring are generally female who produce live young asexually.

f. Towards the end of the season both male and females are born so that eggs can be produced for overwintering.

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g. During the spring and summer, females produce live young without mating.

h. In addition, they can complete a life cycle in as short as one week during the warm summer months.

i. The short generation time and ability of these aphids to reproduce asexually allows them to rapidly increase their populations and feeding injury to apple trees.

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Nymph

Nymph

Adult

Adult laying eggs

Eggs

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2. Damage a. Aphids feed by sticking their mouthparts into the

leaf and sucking out the sap. b. Leaves affected by aphids will often appear dried

and shriveled. Aphids produce a secretion called honeydew.

c. If large populations of aphids are present this honeydew can drip down onto fruit or other parts of the tree and cause sooty mold.

d. This will reduce marketability of fruit and weaken the tree.

e. Established trees are rarely damaged as any minor leaf loss will not have a major impact on fruit production.

f. Young trees can be greatly damaged or even killed if aphid infestations are too high.

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3. Controla. Natural enemies include lady beetles,

lacewings, parasitic wasps and certain fungi.

b. Organic insecticidal sprays are effective and often include liquid dishwashing soap.

c. Because of their size, aphids are often easily controlled by a strong blast of water to displace them from the leaves of the affected plant.

d. Dry weather also greatly reduces the population.

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C. Wooly Apple Aphid (Eriosoma lanigerum)1. Life cycle and description

a. Wooly Apple Aphid produces live young.b. The nymphs are about 1.25 millimeters long and

are reddish purple in color covered in a white cottony wax.

c. Wooly Apple Aphids (WAA) overwinters as nymphs.

d. The adults are about 1.5 millimeters long and similar in color to the nymph.

e. Females are generally observed on the apple tree, males are rare.

f. Females produce live young without mating.

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Left: first instar aphid. Middle: female carrying one egg. Right: Male aphid

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2. Damagea. WAA can attack the roots and

cause galls.b. Over several seasons the galls

will increase in size and cause major root damage.

c. Similar to the Apple Aphid, the WAA produces honeydew causing sooty mold on the fruit and tree.

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3. Controla. The most important natural enemies are green

lacewing larvae, lady beetle adults and larvae, and syrphid fly larvae.

b. Flowering plants in or on the borders of orchards provide nectar and pollen, which helps maintain and attract natural enemies.

c. If replanting or starting a new orchard, plant resistant rootstock.

d. The Malling Merton (MM) rootstock series, MM.106 and MM.111, have been bred to be resistant to WAA,

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e. WAA are easily controlled with broad-spectrum insecticides.

f. In order to significantly increase insecticide efficacy, it is recommended a horticultural oil be added to the tank mix.

g. Without horticultural oil the insecticide has difficulty penetrating the waxy covering of the colony.

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D. Green peach aphid (Myzus persicae) 1. Life cycle and description

a. Eggs are deposited on Prunus spp. trees.

b. The eggs measure about 0.6 mm long and 0.3 mm wide, and are elliptical in shape.

c. Eggs initially are yellow or green, but soon turn black.

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d. Mortality in the egg stage sometimes is quite high.

e. Nymphs begin greenish but turn yellowish.

f. Adults can be winged or wingless.

g. They have a black head and thorax and a yellowish green abdomen.

h. They measure 1.8 to 2.1 mm in length.

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2. Damagea. Green Peach Aphids will travel to any

plant available and will deposit a few young and then move on to another place.

b. Aphids will then begin to colonize on peach trees when the leaves begin to turn color and fall off.

c. The Green Peach Aphid damages trees much like the other aphids- by sucking out the sap from leaves and tender stems.

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d. The major damage caused by the Green Peach Aphid is through the transmission of plant viruses.

e. Both nymphs and adults can spread the virus, but adults can spread it more because of their mobility.

f. Over 100 viruses have been identified to be carried by the aphids.

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3. Controla. Natural enemies of the Green

Peach Aphid are the same as the other aphids- lady beetles, lacewings and parasitic wasps and fungi.

b. Using horticultural oils and insecticides are a very effective way to control large outbreaks.

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E. San Jose scale (Aspidiotus perniciosus)1. Life cycle and description

a. Partially mature nymphs overwinter on branches and in spring developed into winged males or females which do not move.

b. When the weather is warm and trees have budded out, females will lay eggs which hatch immediately.

c. The young are called crawlers.

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d. They look for new shoots and settle to feed until adults where they will overwinter to complete the cycle again.

e. Multiple generations per year are possible.

f. Scale is a very tiny insect covered in a scab-like structure.

g. If the scale is removed a yellow body can be seen.

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2. Damage a. San Jose scale can infest

branches, shoots, leaves, and fruit. Adults and nymphs suck plant juices and cause considerable damage. They have been known to seriously weaken branches and main scaffold limbs, thus causing permanent injury to mature trees. Crawlers settling on fruit may cause fruit spotting.

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3. Control a. Oil sprays can be effective in

controlling low to moderate populations of San Jose Scale.

b. Native predators are also very effective.

c. Predators include the twicestabbed lady beetle, Chilocorus orbus, and another small beetle Cybocephalus californicus.

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F. Olive scale (Aspidiotus hederae)1. Life cycle and description

a. The adult female scale is about 0.10 (2.5 mm) inch long, with a grayish, oval, waxy covering.

b. The male scale is more elongate with a black spot at one end.

c. If the coverings are removed, the scale bodies of both sexes are reddish purple.

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2. Damage a. Olive scale feeds on twigs, leaves,

and fruits.b. The first brood will emerge early in

the growing season and eat the young rapidly growing fruit.

c. A second brood in mid-season causes purple spotting on the green fruit.

d. Heavy infestations greatly reduce the productivity of the tree.

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3. Controla. Olive scale is effectively

controlled by natural enemies such as Aphytis maculicornis and Coccophagoides utilis.

b.Chemical treatment is rarely needed unless the biological control is disrupted.

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G. Citrus Whitefly (Dialeurodes citri)1. Life cycle and description

a. Adults are white and have a distinctive Y-shape on their back.

b. Whiteflies develop rapidly in warm weather, and populations can build up quickly in situations where natural enemies are destroyed and weather is favorable.

c. They grow in stages.i. the first nymph is a very small crawler, later

nymph stages settle and remain immobile and are flattened and oval.

ii. Older nymphs do not move.iii. Finally a winged adult emerges.iv. All stages feed by sucking juices from leaves.

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Nymph

Nymph

Adult Adult and eggs

Colony Citrus spp.

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2. Damagea. Whiteflies suck sap out of the phloem.b. Large populations can cause massive leaf

death.c. Whiteflies produce honeydew like aphids

so black sooty mold can occur.d. Low levels of whiteflies are not generally

damaging but some adults can carry plant pathogens.

3. Controla. Large populations of whiteflies are hard to

control and can be adequately controlled by beneficial insects.

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H. Citrus Leafminer (Phyllocnistis citrella)1. Life cycle and description

a. Adults are very small, about 4 mm wingspan, with white and silvery iridescent scales on the forewings.

b. There is a noticeable black spot on each wing tip.

c. The hind wings and body are white, with long fringe scales extending from the hindwing margins.

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d. Larvae are very small (3mm) and translucent yellow-green.

e. They can be found on the underside of leaves creating meandering paths inside the leaf.

f. Usually only one leaf mine is present per leaf but heavy infestations may have two or three mines per leaf.

g. larvae are protected within the leaf during their feeding cycle.

h. Larvae have four instars and development takes from five to 20 days.

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i. Pupation is within the mine in a special pupal cell at the leaf margin, under a slight curl of the leaf.

j. Pupal development takes six to 22 days.

k. Adults emerge about dawn and are active in the morning; other activity is at dusk or night.

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Adult Egg

LarvaePupa

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2. Damage a. Larvae mine into the leaves of citrus

trees.b. They eat through the leaf destroying

tissue and disrupting nutrient transfer. (see picture on bottom right of slide #51)

3. Controlc. Biological control and application of oil

are suitable methods to help reduce populations.

d. Because of their position inside the leaf, larvae may be hard to eliminate.

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I. Codling moth (Cydia pomonella)1. Life cycle and description

a. The Codling Moth is the main pest of apple.b. The adult moth is greyish with light grey and

copper stripes on its wings, with a wingspan of 17 mm.

c. The females lay eggs on fruit or leaves and the black-headed yellow larvae attack the fruit immediately upon hatching.

d. Each larva burrows into the fruit, eats for around three weeks, then leaves the fruit to overwinter and pupate elsewhere.

e. They mainly feed on the seeds of the apple.

55Larvae

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2. Damagea. Larvae bore into the interior of

the apple consuming the seeds and apple.

b. The infected fruits will often abort and fall off the tree.

c. Once the caterpillar has entered the apple it is of no use as a marketable fruit.

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3. Controla. Insecticides are generally the best method of

control for Codling Moths.b. Because of their location inside the apple,

they are protected from any natural enemies, leaving biological control out of the control methods.

c. Another method for control and sampling, 'trunk banding', consists of wrapping a corrugated cardboard strip around the tree trunk.

d. Larvae making their way back to the tree to pupate after the infested fruits are aborted will use bands as pupation sites.

e. Bands may then be removed and burned.

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J. Red spider mite (Tetranychus telarius)1. Life cycle and description

a. The adult female is approximately 0.65 mm long, rotund oval in shape, and pale yellow or greenish with two characteristic lateral dark green or black spots on the body.

b. The adult male is slightly smaller than the female and has a narrower, more pointed abdomen.

c. Eggs are spherical and very small (about 0.1 mm in diameter).

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d. Nymphs vary in coloration, depending on their host plant, but are normally pale yellow, pale green, or beige, with two green spots.

e. Frequently the end of the abdomen is a dark green.

f. The first stage is six-legged while the second stage is eight legged.

g. The adult females overwinter to begin the life cycle the next season.

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Eggs

Mites’ clumping habit

Adults

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2. Damagea. The Red Spider Mite will attack

grapes, raspberries and tree fruits.

b. They damage the plant by piercing the plant cells and sucking out the contents.

c. This results in a noticeable pale colored spotting on the topside of the leaf.

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3. Controla. There are a number of miticides

available for mite control in the orchard.

b. However, mites rarely reach a level that can cause major economic damage to an orchard.

c. In general, if fruit trees are healthy and well established a mite population will not have a major impact on production.

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K. Oriental mite (Eutetranychus orientalis)1. Life cycle and description

a. Adult females are larger than the males.

b. They are oval and flattened and are often pale brown through brownish-green to dark green.

c. The citrus brown mite can only be identified by the adult male and is easily mistaken for the Texas citrus mite (E. banksi).

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d. Females begin to lay eggs when only a few days old.

e. The eggs are laid along the main veins of the host plant leaves and hatch after a week or less.

f. The length of the entire life cycle is around 10-12 days.

g. Adult longevity lies between 1 and 3 weeks.

h. Under optimal conditions, there can be 10-30 generations per year, depending on the geographical location.

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Oriental red mite, left male on top of a darker female. Right males clustering around a pre-adult female

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2. Damagea. The presence of E. orientalis can be detected

by discoloration of the host leaves and pale-yellow streaks along the midribs and veins.

3. Controla. Oriental mites are primarily found on citrus.b. There are a number of miticides available

for mite control in the orchard.c. However, mites rarely reach a level that can

cause major economic damage to an orchard.

d. In general, if fruit trees are healthy and well established a mite population will not have a major impact on production.

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This is damage done by Oriental Mites on a palm. The damage will look similar on fruit trees- discoloration of the leaf especially along the midrib.

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Review/Summary

1. What is the common terminology used to describe an insect’s life cycle?

2. What are some common orchard insects and how can they be controlled?