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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 PG 1 of 8 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) PG 2 of 8 August 2001 © Copyright NZ Avocado Growers Association 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. August 2001 PG 3 of 8 Pests 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 PG 4 of 8 August 2001 Thripobius semiluteus attacking a thrips larva © Copyright NZ Avocado Growers Association 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 PG 5 of 8 Pests 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.) PG 6 of 8 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 © Copyright NZ Avocado Growers Association 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. Fullers 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 1990s 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 © Copyright NZ Avocado Growers Association 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. August 2001 PG 7 of 8 Pests Avocado Growers Manual 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 PG 8 of 8 August 2001 © Copyright NZ Avocado Growers Association