Control of Insect Pest Incidences in Commercial Forestry

Abstract of a Presentation conducted by 

Tharindu Dilshan

Department of Forestry and Environmental Science

University of Sri Jayewardenepura, Sri Lanka

Commercial forestry aims to get maximum production of timber or other forest products as a business enterprise. However pest outbreaks cause devastating losses in commercial forestry sector. Therefore the pest outbreaks in commercial forest plantations should be controlled in effective manner.

In nature, most insect species are in a balance. However with catastrophic influences this natural balance can change favoring the insect species. This type of insect pests are called as indigenous insect pests. The introduction of new pests can also be catastrophic to natural environments, particularly where similar species do not occur naturally. Those type of insect pests are called exotic insect pests.

Teak skeletonizer, teak defoliator, teak stem borer and Hypsipyla shoot borers in Meliaceae are several insect pests which are causing damages to the Sri Lankan forest plantations.

Monitoring of insect pest diseases in forestry primarily can be done in three ways such as mechanical control, biological control and chemical control. In the late nineties, with the awareness about adverse effects of chemical control of insect pests integrated pest management concept was formed. Integrated pest management has two processes called decision process and action process. In decision process, a rational decision should be taken with available data. Then in the action process the decision comes in to the action. There are two strategies using here such as preventive strategies and suppression strategies. Under preventive strategies regulatory, cultural and genetic tactics are using prevent the insect pest incidents. Under suppressive strategies methods such as mechanical, biological and chemical control are using. The important thing is in integrated pest management, chemical control methods are using in the essential occasions only. So the damages to the environment and humans are minimal.

Pest Management in Commercial Forestry

Presented by

Madhushi Weerasinghe

Forest Pest can be defined as “any insect, disease or closely related organism which is harmful, injurious, or destructive to forest or timber”. All parts of a tree roots, stems, foliage, shoots and terminal leaders are vulnerable to attack by pests. Pest damage can range from slight damage that has no effect on the value of the harvested product to severe damage that stunts or kills the trees or reduces their market value. Tree pests include insects and mites, diseases, vertebrates, and nematodes.

There are several common pests that can be commonly seen in commercial forestry. In Tectona grandis the most common insects cause severe damage plantations are Leaf Skeletonizer (Eutectona machaeralis) and Defoliator (Hyblaea puera). In Swietenia macrophylla the most common pest is Mahogany Shoot Borer (Hypsipyla grandella). Moreover, there are insect pests in Eucalyptus grandis, such as Eucalyptus gall wasp (Ophelimus maskelli). Also some pathogens such as Leaf Spot Fungi (Cryptosporiopis eucalypti),Cylindrocladium Leaf Spot Blight-Fungi (Cylindrocladium reteaudii), Botryoshharia Canker (Botryosphaeria spp.) and Bacterial Wilt (Ralstonia solanacerum) are common. In Aquilaria malaccensis, Leaf spot Disease caused by Corynespora cassicola is common. Considering Sandalwood (Santalum album L.) there are some nursery diseases such as Damping off and Pre-emergence wilt.Also forest plantations can be damaged by Elephants and small mammals.

Managing tree pests effectively should be based on thorough consideration of ecological and economic factors. The pest, its biology, and the type of damage are some of the factors that determine which control strategies and methods should be used. Pest management decisions represent a compromise between the value of the product, the extent of the pest damage, the relative effectiveness and cost of the control measures, and the impact on the environment.

Here the concept of Integrated Pest Management (IPM) is mainly used. That relies on an understanding of the ecology of the pest, draws on this knowledge non-chemical approaches that will make the environment less suited to the development of the pest population. Integrated Pest Management practice may involve in the control program, the judicious and sensitive use of pesticides where necessary. There are five major steps in IPM. Monitoring is the first step. Monitoring forests and newly established plantations will help detect problems early, while there is still time to take action. Identification of pests and the diagnosis of pest damage is the second step of IPM. Threshold level is point at which the pest or its damage becomes unacceptable. The threshold level may be related to the beauty, health, or economic value of the tree crop and that comes as the third step of IPM. Selection of management strategy is fourth step and under this there are several management strategies such as, do nothing, cultural management, mechanical management, biological management and chemical management. Evaluation is the final step of IPM. It is very important to determine how effective the management and control tactics are. This information will determine whether any follow-up treatment is needed and will improve management strategies for next year.

Insect Management in Commercial Forestry

Presented by

Pabasara Gunawardane

All parts of a tree are vulnerable to attack by pests. Pest damage can range from slight damage that has no effect on the value of the harvested product, to severe damage that stunts or kills the trees or reduces their market value. Tree pests include insects and mites, diseases, weeds, vertebrates, and nematodes. 

Insects belong to the kingdom Animalia and in the phylum Arthropoda. Insects are categorised under the class Insecta. More than one million different species of insects have been identified. Some insects of orders such as Coleoptera, Lepidoptera, Hymenoptera, Hemiptera, Isoptera and Orthoptera are considered as pests in plantation forestry. Tectona grandis, Eucalyptus sp. Swietenia macrophylla, Santalum album and Aquilaria sp. are some of the major plantation species in Sri Lanka and the world

When consider about the insects, at least 174 species of insects have been recorded from the living teak tree. Most of these insects are not economically significant in their attacks. Teak defoliator (Hyblaea puera) causes severe defoliation and, hence, reduce growth rate of the tree. The larva of leaf skeletonizer (Eutectona machaeralis) feeds on the green leaf tissue between the network of veins, leaving the skeleton of veins intact. The most important stem borer in young teak plantations is Zeuzera coffeae. Another stem borer is Xyleutes ceramicus and it is found in older Teak plantations.

More than 920 species of insects are associated in Eucalypts. The most common pest problem of exotic eucalypts is mortality of saplings caused by root-feeding termites. Eucalyptus Gall Wasp has been reported in Sri Lanka in 2010 and it was successfully controlled by natural enemies of the pest insect.

Mahogany shoot borer (Hypsipyla robusta) outbreak is the most severe pest attack found in Mahogany. It is suggested that the relatively low level of attack in Sri Lanka may be due to good overhead shade where the trees have been planted.

Zeuzera coffease (red borer) Indarbela quardinotata (bark-feeding caterpillar) and Aristobia octofasiculata (heartwood borer) are some of the pests causing considerable damage to living Sandalwood trees. In agar plantation no such serious pests and diseases have been observed. A leaf-eating caterpillar (Heortia vitessoides) is considered to be the most destructive pest causing damage by complete defoliation of agar plantations. When compare with the other countries of the region the status of the pest outbreaks in forest plantations are lower in Sri Lanka.

In earlier attempts to control pest the commonly used method was to kill all the pests and with time plantation managers realized that pests need to be controlled only if they cause economic damages. The pest management concept is used to indicate management of the pest population to limit it to a tolerable level. With the advancement of knowledge and the science the concept of integrated pest management (IPM) has been introduced in order to manage the insects and pests in commercial plantations.

Lack of sufficient scientific research, inapplicability of sophisticated pest management methods used in developed countries and having the low attention on the pest management in forest plantation species by the government are major challenges in insect management in Sri Lankan forestry context.