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Technical annual report 2000-01



Technical annual report 2000-01


Dept. of Regional Development, Primary Industry, Fisheries and Resources technical annual report; Department of Regional Development, Primary Industry, Fisheries and Resources technical and annual report; Reports; PublicationNT; Technical bulletin (Northern Territory. Dept. of Primary Industry and Fisheries) ; no. 295




Made available via the Publications (Legal Deposit) Act 2004 (NT).






Agriculture -- Northern Territory -- Periodicals; Fisheries -- Northern Territory -- Periodicals

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Dept. of Primary Industry and Fisheries

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Technical bulletin (Northern Territory. Dept. of Primary Industry and Fisheries) ; no. 295



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Department of Primary Industry and Fisheries 210 Ants (especially) Iridomyrmex spp. (Hymenoptera: Formicidae) Some species of ants at high densities can severely disrupt IPM programs, particularly those directed towards the control of red scale, honeydew-producing insects such as mealybugs, planthoppers and sooty mould. Honeydew is a favourite food source for several common ant species and ants entering the tree canopy in search of honeydew can interfere with predators and parasites seeking out pest species. Ants act to defend such pests, which are then able to rapidly build up to damaging levels, causing sooty mould stains on fruit or damaging the structure of trees. Observations have been made of some species of meat ant, Iridomyrmex spp., physically chewing the edges of citrus leaves. This behaviour is not understood and occurs only sporadically resulting sometimes in severe damage to new flush tissue. Meat ants give a nasty bite and are a nuisance to people pruning trees. Meat ant activity has been monitored at KRS to establish when ants are most active and damaging to tree crops. From November to March it is necessary to monitor and control meat ants. Bare soil under rows appears to encourage ants to nest because full sun and warm conditions are most suited to tropical ant species. Mulching beneath trees can increase soil organic matter, improve soil structure, reduce root temperature fluctuations and increase soil water retention. Mulching may also deter ants to some extent. Mulch was laid at KRS during July 2001 and ants will be monitored from November to assess the impact on ant numbers. Oriental spider mite Eutetranychus orientalis (Klein) (Acarina: Tetranychidae) Oriental spider mite (OSM) feed on plant tissue including leaves, fruits and green twigs of many host plants. OSM are distributed widely within Australia and are also found in South-East Asia and Africa. In the NT, OSM is found on citrus and other tree crops in the Katherine and Darwin areas. Eggs are deposited on the upper surface of leaves, commonly near the midrib and the life cycle can take as little as 10 days in warm weather. OSM feeds on the upper surface of leaves and exposed surfaces of fruit. Symptoms of mite activity are most obvious on mature leaves, giving them a white, mottled appearance (chlorosis) which then turns yellow and leaves may drop. Fruit is damaged when mite populations are heavy, causing chlorosis and dull patches at ripening. Monitoring results showed that infestations began to build at the onset of the Dry season, around May and remained active through the cooler months. Feeding activity is thought to be interrupted by heavy rains and excessively hot conditions over our Wet season so mites are less common in the tree canopy. Further studies into population dynamics are continuing. Predatory mites are not yet found commonly on citrus in the Katherine area but further studies may reveal these valuable predators. Stethorus sp. (Coleoptera: Coccinellidae) has been common at times and increases in numbers over the Dry season, thereby keeping mite populations in check. Adult beetles and their larvae feed on all mite life stages and especially mite eggs. Other common insects found to be pests on citrus are: red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae); spherical mealybug Nipaecoccus viridis (Newstead) (Hemiptera: Pseudococcidae); fruitpiercing moth Othreis materna (Linnaeus) (Lepidoptera: Noctuidae) cicadas (Hemiptera:Cicadidae); aphids Aphis gossypii Glover (Hemiptera: Aphididae); sap sucking bugs Oncocoris sp., Nezara viridula (Linnaeus) Mictis profana (Fabricius) etc. (Hemiptera: Pentatomidae); citrus butterflies Papilio spp. (Lepidoptera: Papilionidae); grasshoppers, katydids and crickets various species (Orthoptera).