DIAMONDBACK MOTHS

THE DIAMONDBACK MOTH (Plutella xylostella Linn) has been recorded in Malaysia since 1925 (Short abbreviation as 'DBM'). Since 1941, it has been the major pest of crucifers grown in the Cameron Highlands and in the lowlands. I heard about the words or this insects since my secondary studies more than 40 years ago. The knowledge about the pests are more real during the 'farming hands-on project' on the final year syllabus at UPM, Serdang, Selangor. Our group has to declare 'war' against the pests due to severe attack on our crops. The length of the life-cycle is shorter in the lowlands than in the highlands, being 13 days and 27 days, respectively. There are usually four larval instars. A female moth may lay on an average 288 eggs in its life time. The insect occurs in higher numbers in the drier part of the year that was in January, Feburay and Mei-June. Initially the group noticed that nicotine extract was used to control the diamondback moth. However, with the introduction of synthetic organic insecticides, more farmers relied entirely on these insecticides. By 1957, the insect was found to be resistant to the chemical that was DDT and BHC. But we noticed that in the next seven years, malathion, diazinon and dieldrin proved to be ineffective. Within the next five years, the chemical such as endrin, telodrin and trichlorfon had to be replaced. By 1972, the cost of pest control accounted for about 30% of the cost of production of cabbages in vegetable growing at highland area at Cameron Highlands, Pahang, Malaysia. Resistance to insecticides was found to be common and the resistance factor to malathion was 2096. Farmers had by then resorted to mixing two or more insecticides at high concentrations and spraying at frequent intervals. An ecological approach was adopted in Malaysia in the early 1970s. A search for natural enemies resulted in the discovery of Apanteles plutellae Kurdj, Tetrastichus ayyari Rohw, an entomogenous fungus, Entomophthora sphaerosperma (Fres), syrphids and an unidentified chalcid parasitoid. However, existing natural biological control was very variable. Attempts were made to improve the situation by introducing four exotic parasitoids. This article in "Anim Agro Technology", I would like to share the information about the status of Diamondback Moth in Malaysia based on studies by Technical Group on DBM by Department of Agriculture, MARDI and various institutions.

Both Thyraella collaris Grav and Diadegma eucerophaga have established in the Cameron Highlands area especially those area with cabbage and other relevants crops. From my own observation and further studies from the groups, they also been able to conduct and evaluate entomogenous pathogens and other novel control measures. Many attempts have been made to develop a pragmatic pest management program for the crucifer farmers at Tanah Rata, Kg Raja and Brinchang area. The challenge facing the implementation of such a program is in educating the farmers (and their foreign workers - mostly from Bangladesh) to adopt the integrated pest management approach (IPM). Once the futility of a unilateral approach to controlling DBM was recognized, ecological studies were initiated which will aid an integrated pest management (IPM) approach to controlling this pest (Lim 1974, Ooi 1979a). Table 3 summarizes various developments in DBM control in Malaysia and the ccumulation of information that has led to the present situation. As Lim (1982) pointed out, the initial approach to managing DBM in Malaysia should hinge on spraying only when necessary. In order to achieve this, the most rational step is to develop pest threshold levels so that farmers have a criterion to follow before deciding on a spray operation. Even utilizing a tentative threshold level would lead to a reduction in number of sprays applied. 

The study by Jusoh et al (1982) has contributed to an understanding of yield loss caused by DBM and this information has been refined and applied in the IPM trials carried out by Sivapragasam et al (1984). The results showed that the IPM approach could reduce the number of sprays and yet secure marketable crops. More effective pesticide application technology would help in encouraging farmers to reduce their wastage in excessive dosage and spraying (Sivapragasam 1982). Another factor to consider in the IPM approach is the encouragement of biological control. The importance of biological control has been shown by Lim (1982) and Ooi (1979a). Apart from improving the environment to facilitate existing natural biological control (Lim 1982), there is also the possibility of introducing more exotic parasitoids to complement the existing ones. Attempts to do this have been reported by Ooi and Lim (1983) and more work is needed.

The development of other control methods for DBM has also been reported. Choi and Sudderuddin (1979) reported encouraging results with chemosterilants while studies by Tan (1981) have given encouragement to the approach of incorporating insect growth regulators in a pest management program. Laboratory studies by Hussan (1984) also showed that the granulosis virus of DBM could be used to control the pest. All these possibilities should now be pursued actively to improve the present IPM program. As a first step, there should be an urgent attempt made to consolidate all these research efforts. However, research information alone is insufficient in the implementation of a DBM management program. Bringing the information to the crucifer farmers is equally important but this is an area which is very much neglected (Sivapragasam 1982). For the successful implementation of a DBM management program, the farmer must 32 Ooi understand and accept its concept. To achieve this, Sivapragasam et al (1984) proposed that studies be carried out to understand the attitudes and behavior of the farmers. This will facilitate the education of the farmers as well as the education of the scientists as to the needs of the farmers. It is this understanding and co- operation between farmers and scientists that will eventually determine the success and failure of the DBM management program.

By,

M Anem

Senior Agronomist

Jalan Istana, Bandar Melaka,

Melaka, Malaysia.

(8 Syaaban 1434H)