Chapter 6 Forest Insect Pests and their Signs 158 6. Forest Insect Pests and their Signs Imagine, you are suddenly struck with severe knows his/her plants and also knows a bit head ache. Soon afterwards, you start to sweat about the pests that can affect them as well as and you feel very hot. As soon as you get rid the symptoms of plant diseases. of your clothes, your body is shivering. Even Imagine another example: during a visit to two blankets can’t warm you up. Now, your your Hoop pine plantation you find particular neck starts to ache as well and your limbs feel branches starting to wilt and to turn yellow as heavy as lead. From these signs of an and brown. A closer view shows that the wilt illness, the symptoms, you assume that you starts at a distinct and sharp line and affects are suffering from malaria. Since you get the part of the branch towards the tip. But you really worried about your health, you ask a cannot yet find out what causes the wilt, friend to take you to the hospital in order to whether it is microorganisms or animals like seek medical advice. There, you tell the doctor rodents, mites or insects. This is now the about your symptoms and that you believe that difficult part, because very often one can’t see it might be malaria. He checks you and the rat or the caterpillar causing the disease. confirms that the symptoms look very much But a good diwai doctor doesn’t give up that like malaria. The diagnosis of your illness is easily. A further scrutiny might be helpful, so based on the observation of the symptoms that you decide to cut open the affected area of the you described. In order to confirm this branch and as a result you find another diagnosis, the doctor decides to collect a important symptom: galleries in the branch. blood sample and sends it to the lab. The The first step is done now, all the symptoms result of the pathologist confirms your and the are found. In this example, a very close look doctor’s diagnosis - malaria. Since the cause into the galleries uncovers the mystery and of the sickness has been identified as a elucidates the cause of the wilt. Tiny little particular strain of Plasmodium, the doctor black beetles and their white larvae feed can prescribe chloroquine as a curative inside and burrow into the branchlets, causing treatment. After having taken the medicine, the needles to turn into yellow and brown. The the symptoms disappear and your disease is job left to be done is to collect some larval cured. Only when and if the disease has been and adult beetle specimens as well as some of diagnosed, can the disease be cured. A the affected plant material. A view through a curative treatment is not possible if the doctor magnifying glass or a stereo microscope is not able to diagnose the illness, ie. if he reveals that it is Hyrlurdrectonus araucariae. does not know exactly what you are suffering The diagnosis of this disease is confirmed. from. Now curative measures can be taken, for Cultivated plants and all other organisms in instance high pruning if the infestation is not general can suffer from diseases and become yet too severe, otherwise the application of an sick, too. The task of an agriculturalist or insecticide would be justified. It would be a forester is to recognise a disorder and its waste of money and time to apply a pesticide symptoms early enough so that curative if we were not able to exactly diagnose the measures can be applied in time and thus the disease, ie. we were not sure whether an insect plant can be saved. The situation is a bit more or a fungus caused the disease. We might end difficult than in the above example, since we up spraying and wasting an insecticide that is can’t ask the diseased plant what’s wrong with not effective because the disease is a fungal it. A pathologist or entomologist can be infection. engaged to assist in the identification of the In this example the attempt to find the pest pest and to recommend a suitable remedy, but was successful, but even without the it is the sole responsibility of the agricultural- discovery of the beetles, one could have made ist or forester in charge to find out any an exact diagnosis, since there is no other pest abnormal conditions during regular checks of that causes these symptoms. In most cases the crop. A good forester or agriculturalist however, it will be difficult or even unusual to 6. Forest Insect Pests and their Signs 159 detect the insect, for instance because it feeds sucking mouthparts like hemipteran bugs or only during the night or is present for only a mites pierce parts of their host plant, causing short period of time. Then we have to draw up the affected area to become brown or resulting a diagnosis from the symptoms that are often in wilt or a tumour-like growth, but there is available. Therefore an agriculturalist or a never any part of the plant missing. forester has to be familiar with the specific Insect signs such as cocoons, larval skins, symptoms of the various diseases that can eggs or silk shelters are another indication of affect particular crops. The first part of this the kind of insect responsible for particular chapter focuses on the symptoms. Just as a damage and are also very helpful to determine medical doctor uses particular terms to the causal agent. Generally insect damage and describe the symptoms of an illness, there are signs are divided into four categories: certain terms used by professional foresters, · leaf damage agriculturalists, entomologists and patho- · seed and cone damage logists to describe the disorders of a plant. The · shoot, twig, trunk and root damage use of these terms is like a common language understood by various professionals. One of · insect signs the advantages of this is for instance that the However, the damage seen will rarely fit symptoms can be clearly and exactly exactly into one of the categories, more often described by an agriculturalist who is seeking it is a combination of two categories. a piece of advice from an entomologist. The second part of this chapter deals with the various diseases of tree crops in Papua New 6.1.1 Leaf Damage Guinea caused by insects. The symptoms of the diseases, the insects that are responsible · Leaf and needle mines are caused by for the particular damage and - if known - insects with chewing mouthparts Feeding their biology are described. Furthermore, occurs inside the leaf or needle on the meso- suitable remedies for the control of the phyll, between the lower and upper epidermis respective disorders and preventive measures (fig. 6-1 A, B). The different types of mines are discussed as recommended by the Forest are described according to their shape as Research Institute (FRI). linear mine, serpentine mine, blotch mine, digitate mine, leaf blister (fig. 6-1 B), needle mine or a combination of one or more. · External leaf or needle damage is caused 6.1 Insect Damage and Sign by insects with chewing mouthparts feeding Categories externally on the leaf or needle. A leaf or needle chewed from the outside, called free feeding (fig. 6-2 C, G), is sometimes left with A closer look at the damage caused by a only the tough veins and the middle rib as particular insect gives us a general idea of skeleton (skeletonizing, fig. 6-1 D). A small which kind of insect has caused the damage. patch eaten through all layers of the leaf, The signs as a result of an insect with creating a hole in the leaf is referred to as hole piercing-sucking mouthparts look very differ- feeding (fig. 6-1 C). If only one surface of the ent from the feeding traces of an insect with leaf is affected resulting in a more or less chewing mouthparts. Chewing mouthparts transparent ‘window’, we talk about window result in parts of the plant being chewed or feeding (figs. 6-1 C, E). torn off so that there is for instance a hole in a leaf. This type of damage is most likely to be · Stippling damage is caused by the piercing caused by caterpillars of moths and butterflies, and sucking action of hemipterans and mites. by maggots of flies and wasps or by adult Usually these animals inject saliva for the beetles or their grubs. Insects with piercing- external digestion of the plant juices prior to 160 6. Forest Insect Pests and their Signs A B C D E F G H I J Fig 6-1: Leaf damages: (A) leaf mine; (B) leaf blister caused by the leaf blister sawfly Phylacteophaga sp. (Hymenoptera; Pergidae); (C) multiple damage consisting of free feeding, hole feeding and window feeding; (D) sketetonized leaf; (E) window feeding; (F) dead spots; (G) leaf tying and free feeding; (H) leaf rolling; (I, J) leaf galls (photos Schneider, M.F.) their ingestion. The toxic effect of the saliva 6-1 I, J). The immature stages of gall-forming results in small, circular ‘dead’ spots (fig. 6-1 insects develop and feed inside a gall. Galls F) on the leaf. can also be induced by saliva injected during · Shelter feeding refers to foliage that is the piercing-sucking action of Hemiptera and modified into a shelter in which an insect mites. Galls of other plant tissues are shown hides and feeds.