Spring-Feeding Caterpillars

Table of Contents

1. Introduction
2. Leafrollers
3. Green Fruitworms
4. Eye-spotted Bud Moth
5. Tent Caterpillars and Fall Webworm
6. Gypsy Moth
7. Monitoring and Management

Introduction

The spring-feeding caterpillar complex comprised of several species of Lepidoptera (moth family). These include leafrollers, fruitworms, cankerworms, budmoths, tent caterpillars and fall webworm. In general, these caterpillars are active early in the season, from 1/2 inch green to mid- June. The biology, physical description and damage of each group is described below.

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Leafrollers

There are numerous species of leafrollers belonging to a family of moths called Tortricidae that attack apple. These include the redbanded leafroller, Argyrotaenia velutinana (Walker), the variegated leafroller, Platynota flavedana (Clemens), the fruit tree leafroller, Archips argyrospila (Walker), and the oblique-banded leafroller, Choristaneura rosaceana (Harris). All are general feeders, consuming leaves of many species of fruit and shade trees.

The redbanded leafroller (Figure 1) was a major pest in the late 1950s and 1960s when the use of DDT eliminated most of the parasites that normally kept them in check.

Since that time the use of organophosphates has again relegated this insect to minor pest status in Ontario.

Figure 1. Red-banded leafroller moths in pheromone trap.

Currently the leafroller causing the greatest concern is the obliquebanded leafroller (Figure 2) which has become resistant to organophosphate insecticides in some major apple-growing regions in the province.

Most leafroller species overwinter as larvae in hibernacula or as pupae. However, the fruit tree leafroller overwinters as an egg. There are two generation of most leafroller species. Female moths lay eggs on the upper surface of leaves in flattened, overlapping clusters of 20-200 pale yellow to brownish eggs, depending on species.

Figure 2. Larva of obliquebanded leafroller.

Leafrollers become active as soon as green tissue is visible (feeding on young developing leaves or boring into buds). As the leaves expand, larvae begin to web and roll terminal leaves where they remain hidden when not feeding. Leaf feeding, if severe, can reduce photosynthetic activity. Leafrollers can quickly become a major problem in nursery plantings and newly planted orchards if not controlled (Figure 3).

Some leafroller species suspend themselves from silken threads, which allows them to disperse to other trees with the slightest breeze. Infestations are therefore often most severe around the orchard periphery and adjacent to wood lots.

Figure 3. Terminal feeding injury and spring-feeding caterpillar.

Leafrollers will also feed on blossoms and, later, developing fruitlets as well. This early season feeding results in large corky scars and indentations on the fruit (Figures 4 & 5), which often drop prematurely. Summer-feeding on developing fruit will result in downgrading of apples to juice quality (Figure 6).

Figure 4. Aborted fruitlets from early season caterpillar feeding.

Figure 5. Spring-feeding caterpillar injury to mature fruit.

Figure 6. Late season injury to fruit.

Leafroller larvae are generally green with black or brown head capsules. If disturbed they have a habit of violently wriggling backwards. This behaviour, in addition to being an escape mechanism, startles potential predators.

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Green Fruitworms

The most common species of green fruitworm in Ontario orchards is the speckled green fruitworm, Othosia hibisci (Guenee). The pupa overwinters underground. The moths, members of the Moctuidae family, emerge in early spring. After mating, eggs are laid singly on developing leaves and are a whitish grey with distinct ridges on the sides, visible when viewed through a microscope. Larvae, which resemble tiny inch worms when they first hatch, feed on buds, leaves, blossoms and developing fruitlets. The deep corky feeding scars are difficult to distinguish from leafroller injury.

Approximately 70% of attacked fruit will abort prior to or during June drop. Larvae often feed extensively on one fruit, but sometimes can damage up to a dozen or more.

The full-grown caterpillar is quite large, 30-40 mm long and a lime to dark green colour, including the head (Figure 7).

Small white spots cover the body with several white longitudinal stripes running the length of the caterpillar. There is only one generation per year.

Figure 7. Green fruitworm larva.

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Eye-Spotted Bud Moth

The eye-spotted bud moth, Spilonota ocellana (Denis and Schiffermullar), overwinters as a partially grown larva within a silken case attached to the base of spurs and twigs. The larva, which is dark brown (Figure 8), becomes active in early spring, when apples reach the 1/2 inch green stage.

The insect burrows into, and feeds on, opening flower buds and form shelters by tying leaves together. Bud moth larvae will also burrow into developing shoots, which can cause economical damage in nursery and non-bearing plantings when infestations of the pest occur.

Figure 8. Larva of eye-spotted bud moth.

Larva pupate after five to seven weeks and emerge as a small moth with grey and white markings and resembling a bird dropping when at rest. A second generation is active in mid- July through early August. Young larvae from this generation feed on leaf undersides and construct shelters of leaves and frass. Fruit in contact with infested leaves may also be attacked.

The feeding injury is characterized by tiny, shallow, circular excavations on the fruit surface (Figure 9), similar to injury from summer generation obliquebanded leafroller.

Figure 9. Eye-spotted bud moth injury to fruit

Tent Caterpillars and Fall Webworm

The Eastern tent caterpillar, Malacosoma americanum, overwinters as a golden brown egg mass encircling young twigs (Figure 10), often detected during winter pruning. Each eggs mass can have 200-300 eggs.

The eggs hatch in early spring and young larvae spin a characteristic tent in a limb crotch (Figure 11), in which they reside as a colony, leaving only to feed on newly developing leaves in the mornings and evenings.

Figure 10. Eastern tent caterpillar egg masses

Figure 11. Eastern tent caterpillar nest in tree

The full-grown larva is 40 to 50 mm in length, hairy and brownish black with blue spots along the body and a white stripe running the length of the back. One colony can strip the leaves of whole branches. Fruitlets on these branches fail to develop. Adult moths emerge in late June with egg laying occurring in July. There is only one generation per year.

The fall webworm, Hyphantria cunea (Dru.), is not really a spring-feeding caterpillar. The larvae are active from July through September spinning large webs or tents in host trees (Figure 12). Not usually a problem in commercial orchards, they can occasionally be found in apple trees where little or no summer insecticides were used, and in non-bearing blocks.

Figure 12. Fall webworm nest.

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Gypsy Moth

The gypsy moth, Lymantria dispar (Linnaeus) is normally considered a forest pest.The species, introduced from Europe, is very cyclical, with population exploding roughly every 10 years. The overwintering egg masses, consisting of 500 eggs or more, are laid on tree trunks, usually within several feet of the base. These masses are several centimetres in diameter, a pale yellowish brown and covered with hairs from the female's abdomen. Eggs hatch around the petal fall period on apple. Young larvae disperse on silken threads, a behaviour called "ballooning", into orchards from adjacent hardwoods.

The larvae are very hairy and black with five pairs of blue dots, and six pairs of red dots along the back (Figure 13). Feeding is restricted to leaves. Young larval feeding results in small pinhole-type injury (Figure 14) while older larvae consume whole leaves.

Figure 13. Gypsy moth larva

Figure 14. Gypsy moth "shothole" feeding injury on leaves.

Caterpillars pupate on tree trunks. The adult is active in July. Females are cream coloured, heavy bodied and do not fly. The males are brown, smaller than the female and have feathery antennae. There is one generation per year.

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Monitoring and Management

Since spring-feeding caterpillars feed on a wide variety of deciduous trees and shrubs, herbaceous plants and brambles they are most often detected in apple orchard peripheries adjacent to these alternate hosts. However, many species are dispersed by wind currents deeper into the orchard interior, so monitoring should not be restricted to the orchard perimeters.

Note that, especially in early spring, tiny larvae in buds and developing terminal are difficult to detect without pulling the plant tissue apart and observing with a 10x or 16x hand lens.

Tent caterpillar, webworm tents and gypsy moth activity can be noted during regular orchard inspections while monitoring for other pests.

Depending on spring temperatures, timing of this spray may occur either per-bloom (usually at pink) or at petal fall. Insecticide options are defined in the Pest Management Decision Guidelines in Chapter Five of Publication 310: Integrated Pest Management for Ontario Apple Orchards.

Tent caterpillar and webworm tents do not require insecticide treatment. Pruning out of infested branches is the most practical approach.

Gypsy moth caterpillars require no special monitoring and are normally controlled with petal fall insecticides applied for other pests.

Many predatory and parasitic insects attack spring-feeding caterpillars. Predators include ground beetles (Carabidae), stink bugs (Pentatomiidae), assassin bugs (Reduviidae), and spiders. Birds such as chickadees, bluebirds, warblers and woodpeckers also predate heavily on caterpillars. Parasitic wasps (Braconidae, Ichneumonidae) and flies (Tachinidae) attach caterpillars and minute Trichogramma wasps often parasitize moth eggs. A number of fungal and viral diseases also impact on caterpillar populations, particularly during warm, wet springs.

To conserve and encourage natural enemies of spring-feeding caterpillars, apply insecticides only if the action threshold is reached and then select the most benign and narrow-spectrum materials available.

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