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Plantwise Technical Factsheet

dry wood termite (Postelectrotermes militaris)

Host plants / species affected
Acacia decurrens (green wattle)
Camellia sinensis (tea)
Casuarina equisetifolia (casuarina)
Cedrus (cedars)
Cinnamomum camphora (camphor laurel)
Cryptomeria japonica (Japanese cedar)
Erythrina subumbrans (December tree)
Eucalyptus robusta (swamp mahogany)
Eucalyptus spp.
Grevillea robusta (silky oak)
Stenocarpus salignus (Beefwood)
Tephrosia vogelii (Vogel's tephrosia)
List of symptoms/signs
Roots  -  internal feeding
Stems  -  internal feeding
Whole plant  -  internal feeding
Symptoms
P. militaris rarely produces winged forms and its spread to healthy bushes is mainly through contact with the roots of neighbouring bushes. This explains why attacks are confined to groups of about 10 bushes in a patch, although up to 200 bushes may be affected in a patch (Seneratne, 1986). Hutson (1923) considered P. militaris the most formidable tea pest as it is often not noticed during the early stages of attack. Infestation begins in a side root and the galleries extend upwards towards the main root, other roots, rootlet stems and branches. During this process, only the heart wood is consumed, the sap wood remains untouched and the plant functions normally. Apart from wilting of some branches, particularly during drought, the infestation progresses unnoticed until wide galleries in the branches reach about 2ft above the ground and become exposed at pruning. In cases of prolonged attack, often only the external shell of the plant remains. The hollowed out cavities in stems and branches are filled up with earth-like matter comprising mainly of termite faecal matter (Pinto, 1941; Rananweera, 1962; Cranham, 1966).
Prevention and control
Early Detection

As a cryptic pest, P. militaris is very difficult to detect until the galleries reach the branches when they can become exposed during pruning. The possibility of using a microphone and electric telephone for the detection of P. militaris was investigated by Snyder (1948) in the 1940s. This work was revived in 1990s at the Tea Research Institute in Sri Lanka when a portable ultrasonic detector with specific sensors was developed to detect the presence of cavities formed by P. militaris in tea bushes. However, due to problems including high cost this method was considered unfeasible for use in the field (Thirugnanasuntharan, 1991, 1992).

Cultural Control

The advanced stage of termite infestation within the tea bush can only be detected at pruning time. When such infestations are noticed, the frames of adjoining bushes are also examined for signs of galleries and the infested bushes, along with two concentric rings of bushes surrounding them, are also uprooted until they show no sings of termite attack. Following uprooting, the patch is thoroughly forked to remove all roots, which are then burned in situ. As it is not practical to remove all roots, there is always the chance that a few small roots will be left behind to carry residual populations, from which re-infestation could occur. To prevent the build-up of these residual populations, the uprooted area is planted to a non-host soil rehabilitation crop for an extended period (4 years), during which time the root fragments decay along with the termites within. Thereafter, the field is either infilled or replanted depending on the size of the uprooted patches (Anon., 1983; Seneratne, 1986).

Use of Resistant/Tolerant Clones

Screening clones for resistance/tolerance to P. militaris under field conditions would take a long time. Laboratory methods, in addition to field experiments, have therefore been used to screen clones for resistance/tolerance to P. militaris over a shorter period of time and have proven to be very reliable (Thirugnanasuntharan, 1987, 1988, 1989,1990).

Biological Control

Due to the concealed habitat of P. militaris, it has not been possible to control this pest using insect parasites and predators. However, this habitat shows some promise for soil-borne entomopathogens, such as entomopathogenic nematodes. Studies carried out under laboratory conditions revealed that Sri Lankan isolates of the entomopathogenic nematodes Heterorhabditis spp. and Steinernema carpocapsae were better control agents than commercial formulations of S. carpocapsae (Biosafe) and S. feltiae ('Nemasys') imported from Biosys, California, USA, and the Agriculture Genentic Company, UK, respectively (Amarasighe and Hominck, 1993a). However, the effectiveness of these isolates under field conditions has yet to be proven. Field studies carried out with commercial formulations of S. carpocapsae and S. feltiae gave good control only at the higher dose of S. carpocapsae, however, these results were not consistent (Amarasinghe and Hominick, 1993b).
Impact
Although a serious pest of tea, P. militaris, is localized and distributed mostly at high altitudes (>1000 m a.m.s.l.). It can only be detected at the late stage of infestation due to its cryptic habitat. At this stage, the tea bush is too debilitated for revival and has to be uprooted, causing a loss of about 40% of the total stand in that location (Sivapalan, 1999).
Related treatment support
 
External factsheets
DPI NSW factsheets, New South Wales Government, Department of Primary Industries, Australia, 2014, English language
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