VOLUME 18 PART 5 The Use of Light Traps to Control the Lachnosterna bidentata Burm. in Malayan Rubber Plantations

B. SRIPATHI RAO

Light traps developed over five annual flighting seasons gave promising results for the control of Lachnosterna bidentata Burm. in immature rubber plantations. The preferred design was illuminated by a 15-watt blacklight fluorescent tube and operated from a car battery. A study of the flighting habits of the showed that the trapping time could be limited to about 42 hours in a season.

One of seven of Melolonthid young plantation to another as the first affected whose grubs are known to infest the soil of fields lose their cover. rubber plantations in Malaya, Lachnosterna Economic considerations at present limit (Holotrichid) bidentata Burm. is a pest of im- the use of chemical treatment of the soil to mature plantations. Outbreaks are sporadic, protecting the main roots of the young rubber. generally occurring from about the second To be able to catch the beetles during their year, when the leguminous ground covers be- flight to the forest and back to the plantation tween the rows of rubber trees become fully after feeding and mating, thereby preventing established, to the fifth year, after which the them from laying eggs and initiating a new covers are largely shaded out. The females attack, promises great advantages. With this are apparently attracted to oviposit under the objective, light traps of various designs were legumes. There is an annual life cycle, the operated during the flighting season of larval stages lasting from about May to 1960-1964 in areas heavily infested with L. October, beetles emerging from the ground bidentata grubs in the previous year. during February and March of the following year and flying to the forest to feed, as they TRAP DESIGN AND OPERATION do not feed on rubber leaves. Outbreaks are There were three basic trap designs (see therefore confined to areas adjacent to pri- Figure 1), one to accommodate a bulb shining mary or secondary forest. upwards (A); one to take an 18-inch fluores- Attention is first drawn to an infestation by cent tube (B); one for a 12-inch, diameter the cover plants dying in patches which extend circline fluorescent tube (C). The traps until the cover is destroyed. Only then do used were: B4, an enlarged version of the the grubs attack the rubber roots, starting Pennsylvania trap of FROST (1957), with with the rootlets and progressing along the a straight fluorescent tube and four laterals, ultimately feeding on the tap root. vanes 8 in. wide and 19 in. high; A4, Small trees may be killed; better established a further modification to take a bulb and trees may lose their leaves and die back if not also having four vanes; C3, fitted with a circ- protected in any way. In eight areas in conti- line tube and having three vanes. All were guous parts of the states of Malacca, Johore constructed from 20-gauge aluminium sheet. and Negri Sembilan, outbreaks have in recent A circular rain shield was attached to the top years recurred annually over periods varying of the vanes and at the lower end to a 60° from two to seven years, spreading from one funnel of 20 in. diameter, narrowing to a

COMMUNICATION 374 243 Journal of the Rubber Research Institute of Malaya, Volume 18, Part 5, 1964

2 in. hole. The apex of the funnel projected of 1960) totalling nearly 60 thousand beetles, about two inches through the lid of a were distributed. collecting bin. The vanes and the inner sur- Power consumption. Trap A4-bb, the most face of the funnel were painted black; Frost successful of the three, had the disadvantage obtained higher catches when reflections were of high power consumption, limiting its use thus eliminated. to areas near a power line. Trap B4-bt, the next best, consumed so much less power that History of Trap Modifications it could be operated from a 12-volt car battery, Light source. Initially three light sources through a vibrator converter or a transistor were compared: a 125-watt black light bulb converter. (bb) and a 125-watt mercury-vapour bulb (wb) A unit of one battery and one vibrator con- in trap A4, and a 15-watt 18-inch blacklight verter was found to be sufficient to work four fluorescent tube (bt) in trap B4. The traps B type traps connected in parallel; as the were hung on posts to carry the centre of the current consumption is about ten amperes, a light source about six feet above ground. The 50 amp-hour battery operating for an hour posts were spaced about 100 yards apart in a a day requires recharging not more frequently line in a heavily infested area, and the traps than every three days. Transistor converters, were rotated daily so that each was operated used in 1964, considerably simplified the traps an equal number of days in each position. and their operation, but they did not make This principle was adhered to in all subsequent them any cheaper as a separate one was tests. Figure 2 shows how the catches in the required for each trap. three traps (operated daily between 7.00 p.m. Number of vanes. Reducing the number of and 10.00 p.m. during the peak flighting season vanes from four to three did not make much Q

Figure 1. Trap designs A (left), B (middle) and C (right).

244 B. S. RAO: The Use of Light Traps to Control L.bidentata in Malayan Rubber Plantations

I 125-waft blacklight bulb

Q 15-watt blacklighf tube

| 125-watt mercury-vapour buib

1 Ik nTli March ! April Figure 2. Comparative daily catches of beetles with three light sources during peak flighting season of 1960 (/5 March to April 4) difference to the catch: the results were 21 Size of trap. An enlarged B3 design with thousand for a B4-bt trap and 20 thousand for a funnel 24 inches in diameter instead of 20 a three-vaned version of it (trap B3-bt), com- inches and vanes 10.5 inches wide instead of pared from 17 to 26 March in 1962 (Table 1). 8 inches, but with the same light source (trap Loss of catch on the ground. Many beetles Bi3-bt), tested in 1963, caught more beetles that were attracted to the light fell short of and reduced ground losses. Two such traps the trap on the ground, settling on the illumi- caught a total of 42 thousand beetles during nated cover or foliage of rubber trees nearby, the whole of the flighting season, compared their numbers decreasing with distance from with 96 thousand caught by six B3-bt traps. the trap to about twenty feet. Trap design Further enlargement of the trap (using a C3 was an attempt to reduce this loss of catch. funnel 32 inches in diameter and vanes 14.5 Illuminated by a 32-watt blacklight circline inches wide (trap B23-bt) tested between 4 fluorescent tube (be), it was compared with a March and 2 April 1964, resulted in a further B3-bt trap, the losses being calculated by increase in catch: 6.8 thousand compared counting the beetles recovered from a 10x10 with 5.7 thousand caught in a Bi3-bt trap. ft sheet of black net spread on the ground Height of trap. The height effect was just below each trap. The total catches of studied during the same period, operating a beetles and the percentage losses on the ground Bi3-bt trap at three feet, six feet and ten feet over the sampled area during the flighting from the ground. At three feet the ground season of 1962 did not differ materially: 30 immediately around the traps is brightly thousand and 5.1 % for C3-bc and 31 thousand illuminated, while at ten feet much light shines and 3.2% for B3-bt. on the canopy of the rubber trees nearby,

245

COPYRIGHT © MALAYSIAN RUBBER BOARD Journal of the Rubber Research Institute of Malaya, Volume 18, Part 5, 1964 resulting in both cases in considerable loss of unit permits the operator to visit the traps beetles outside the trap. Though the catches only once a day, at any convenient time, to at the three different heights did not differ empty out the catch and replace the bin. If markedly—6.1 thousand, 6.3 thousand and the catch is to be taken nightly, after the traps 6.9 thousand respectively— losses on the are switched off, the bin may with advantage ground over a sampled area of one hundred be replaced by a large polythene bag (Figure 3). square feet immediately below the traps were Alternatively, the catch can be automatically 4.5%, 1.9% and 0.5% respectively. Losses disposed of into the soil by replacing the bin resulting from the beetles settling on the illumi- with a 3-inch diameter cylinder leading from nated foliage of rubber were not assessed. the funnel into a large hole in the ground Transparent vanes. The effect of having covered with a sheet of metal, the bottom and transparent vanes was tested between 25 sides of the hole being sprayed or dusted with February and 3 March 1964, when two traps a heavy dose of a contact insecticide to kill with vanes of transparent perspex sheets the beetles falling into it. (Trap Bi(3)-bt) caught a total of 10.2 thousand beetles, as against 12.1 thousand caught by SUMMARY OF RESULTS two similar traps, but with the standard vanes The numbers of beetles caught with different of black painted aluminium sheets. type of light traps operated on seven sites Disposal of beetles. Once inside the bin the during the five years are summarised in beetles are unable to get out; they can be left Table 1. Subsequent to trapping, these areas there to be collected and killed the next day. suffered only negligible damage or were not Incorporating a time-switch to control each reattacked at all, except Site 1 which was

Figure 3. Trap B\3-bt (left) with the bin replaced by a poly- thene hag, (right) with a device for automatic disposal of beetles into the soil.

246 B. S. RAO: The Use of Light Traps to Control L.bidentata in Malaya Rubber Plantations reattacked moderately severely—hence the by pouring four pints of 0.1% heptachlor repetition of trapping there. emulsion into crowbar holes around the bole, this being the standard treatment recommen- COMPARISON OF TRAPPING ded in all cases of cockchafer infestation in WITH SOIL TREATMENT young rubber. During the subsequent flighting The relative effectiveness of trapping and of season, trapping was conducted over an insecticidal treatment of the soil were com- area of approximately 150 acres of the field pared at Site 5, where a 40-acre section of the excluding the 40-acre section. Grub counts affected area projecting into the jungle in a made a year after the soil treatment in ten- U-shape was divided into four 10-acre plots yard-square pits dug at random in the plots in a line. In alternate plots, 25 pounds per treated with insecticide and in a like number acre of 10% heptachlor granules were broad- of pits in the control plots, as well as in the cast at a time when the grubs were actively rest of the previously affected area where light feeding. The rubber trees were treated to traps had been operated, gave averages of 2, protect the tap root and the bases of laterals 46 and 9 grubs per pit respectively.

TABLE 1. NUMBER OF L. BIDENTATA BEETLES CAUGHT IN LIGHT TRAPS IN SEVEN SITES OVER FIVE YEARS

Year Dates Trap design No. of traps Site Acreage Total catch Catch per trap

A4—b b 1 28,447 28,447 1960 10.2 to 13.4 A4 —w b 1 1 100 12,076 12,076 B4— bt 18,722 18,722 2 1 100 42,050 21,025 1961 10.2 to 30.4 B4—b t 2 2 20 33,220 16,610 2 3 10 14,606 7303 17.3 to 26.3 B4—b t 1 21,302 21,302 27.2 to 16.3 \ 10,643 \ 1962 17.3 to 26.3 f B3—b t 1 4 100 20.270J 30,913 27.2 to 26.3 C3—b e 1 30,047 30,047 B3— bt 6 5 150 96,851 16,142 1963 28.2 to 7.4 B3— bt 6 150 110,675 18,446 Bi3— bt 2 i 42,262 21,131

25.2 to 3.3 \ Bi(3)—b t 2 10,262 5131 Bi3— bt 2 12,101 6050 1 1 at 3 ft 6135 6135 1964 Bi3—b t \ 1 at 6 ft 7 20 6330 6330 4.3 to 2.4 1 1 at 10 ft 6901 6901 Bi3— bt 1 5699 5699 1 I B23—b t 6835 6835 Key to Trap Designs A, B and C Trap designs with 20 in. diameter funnel Bi and B2 Design B with 24 in. and 32 in. diameter funnels respectively 3 and 4 Number of vanes; transparent if bracketed bb 125-watt blacklight bulb wb 125-watt mercury-vapour bulb bt 15-watt blacklight fluorescent tube be 32-watt blacklight fluorescent circline tube

247 Journal of the Rubber Research Institute of Malaya, Volume 18, Part 5, 1964

The advantage appearing to lie with the In 1960 the traps were operated from 7.00 chemical treatment rather than with trapping, to 10.00 p.m. The catches for the three suc- it is of interest to compare the costs of the cessive hours, roughly in the proportions of two operations. Broadcasting heptachlor gra- 7:2:1, are illustrated in Figure 5. nules cost MS25.00 per acre. A set of four Almost all the beetles collected during the traps with battery, converter and cables cost early days of the flighting season are males, around MS400.00. The two units (costing but the proportion of females steadily increases $800) operated on Site 5 effectively covered an until, towards the end of the season, almost area of 150 acres and the cost of trapping for all are females. Figure 6 shows the proportion one year can thus be estimated to be just over of males and females in the daily catches in MS5.00 per acre, the cost of operation being 1960 and 1961, the ratios over the whole extremely low. As capital costs are charged season being 9:11 and 2:3 respectively. As against the first year, the units can be operated the trend of increase of females with the prog- in subsequent years at almost no cost. ress of the season was similar in all the three Incidentally the total number of beetles sites where trapping was done in 1961, the caught in traps on Site 5 (139 thousand) was catches from them were combined in the perhaps only about half of the total number figure. destroyed because of the exceptionally high During and after the peak flighting season, proportion that fell outside the traps that year beetles can also be seen to fly into the planta- and were killed by spraying the ground around tion from the jungle just after dusk and at the traps. daybreak; but there is no massed return of FLIGHTING HABITS AND SEX RATIO those that have fed and copulated in the OF THE BEETLE jungle. Emerging from the pupal case during dry A check on the gut contents of all the weather in late December or early January, beetles trapped in 1961 in three areas, squeezed the beetles remain below the ground until the out through the anus by pressing the abdomen, drought is broken, whereupon they burrow showed how the proportion that had fed and out of the soil in large numbers and swarm returned to the plantation rose from 0 to towards the jungle. The flighting season ex- 100%. A rise was also noted in the pro- tends from the latter part of February until portion of gravid females during this period, early April, with varying peaks of activity studied from the ovaries expelled at the same following rain between dry days. Beetle time. These are illustrated for 1961 in Figure catches in the five years of operation of the 7, where again the catches from the three traps are plotted along with rainfall in Figure 4. sites are combined. The emerging beetles make a neat cylindrical DISCUSSION hole about a centimetre in diameter and wait Light traps have proved valuable tools for the for darkness just below the soil surface. Just collection and study of many species of . after 7.00 p.m. they can be seen to push away The attractancy of various wavelengths includ- the soil closing the hole and putting their ing the ultraviolet has been extensively investi- heads out. Emergence takes place when it is gated. FROST (1953 and 1954) established a little darker, between 7.15 and 7.20. Flight- that radiations in the near-ultraviolet (3200 to ing is at its height between 7.20 and 7.45 3800 A) commonly termed blacklight, gene- (during which time the beetles can be seen to rise from the cover and fly in large numbers rally attract more insects than white light of towards the jungle), is reduced after 7.45 and the same intensity. TAYLOR and others (1956) becomes negligible after 8.15. The beetles reported that blacklight attracts almost all are particularly active on moonless nights, but insects of economic importance known to be rain during the flighting hour has a depressive photopositive. TASHIRO AND TUTTLE (1959) effect. caught seventy times as many European

248 •"-- Catch —- No trapping Site I. I960 D Rainfall 12 - (llth Feb-7th Apr)

- / \ A -f

^H-Lr7r"-""""""" - ... __P£^ FHTU ft, FK 1 1 11° [~ Site 1. 1961 - 4 - filth F*b-7th Apr) n/M ..A., I'

Site 4. 1962 24 - f24ih Fab- 7th Apr)

12

iILJ0

Site 5. 1963 16 -. (28th Feb-7+h Apr)

12

-"n

Site 7. 1964 - (25th Feb-2r>d Apr)

February March April Figure 4. The effect of wet weather on the emergence and flighting of beetles. 249 10

] 7pm to 8pm

[] 8pm fo 9pm

| 9pm to I Opm

_ HL Ik Ik. March I April Figure 5. Comparative daily catches of beetles in three hourly periods during peak flighting season of 1960 (15 March to 4 April).

| Males

!; Females

February

Figure 6, Proportion of males and females in daily catches in three traps on one site in 1960 {11 February to 13 April), and in six traps on three sites in 1961 (11 February to 30 April).

250 B. S. RAO: The Use of Light Traps to Control LMdentata in Malayan Rubber Plantations

March Figure 7. Proportion of (A) beetles that had fed and (B) gravid females among rhe female population, both shown in black, in daily catches in six traps on three sites in '1961 (7 March to 30 April). chafer beetles ( majalis Raz.) with the jungle edge would be sufficient to deal blacklight traps as with the most attractive with the beetles emerging in that area or flying chemically baited traps. into it from an infested area deeper in the The efficiency of light traps as a means of plantation. The traps are best hung on posts crop protection has often been questioned, about six feet above the ground, well below and indeed they are unlikely to be of use the leaf canopy of the three ot five-year-old against an which does not have clearly trees. The choice of spacing between the defined swarming times and periods. The traps, taken as 100 yards, remains largely restricted hours of flight and of the flighting arbitrary, and needs further study. season of Lachnosterna bidentata make the One criticism of insect control by light trap- species vulnerable to control by trapping. ping is that the catch comprises mostly males Trapping begins with the first rains during and the females that have already laid their the first two months of the year and occu- eggs (MAHEUX AND GAUTHIER, 1939; HEIT pies one hour per day over a period of AND HENRY, 1940; OMER-COOPER et al., 1941; approximately six weeks. Thus the time GAUTHIER, 1944; TASHIRO AND TUTTLE, 1959; spent in trapping the beetles is only about KALRA AND KULSHRESHTHA, 1961). That L. forty-two hours. bidentata is different in this respect is proved The Bi3-bt trap with an 18-inch 15-watt by the results shown in Figures 6 and 7. blacklight fluorescent tube, 24 in. diameter A possible objection to light trapping is that funnel and 10.5 in. wide vanes (Figure 3) was beneficial insects are destroyed at the same the most satisfactory of the traps tested. time. A typical catch in a plantation of young Further enlargement, unless a folding pattern rubber comprises predominantly Coleoptera, is devised, would make the trap unwieldy for Lepidoptera and Cicadellidae among Hernip- transport. The escape of beetles that alight tera. Winged stages of ants and termites are on the ground can most easily be prevented numerous at times when they are flighting. by spraying the area around the traps with a Small numbers of Orthoptera (Gryllidae, Gryl- strong dose of a contact insecticide. A chain lotalpidae, Tettigoniidae and Blattidae), Der- of traps placed in a line about 100 yards from maptera, (Cicadidae, Lygaeidae,

251 Journal of the Rubber Research Institute of Malaya, Volume 18, Part 5, 1964

Coreidae, Pyrrhocoridae, Pentatomidae and many helpful suggestions and advice in the Reduviidae), Odonata, Ephemeroptera and course of the work and for his assistance in Neuroptera are frequently present. Small preparing the manuscript for publication. Hymenoptera and Diptera are also attracted. Mr K. Suppiah of the Pathological Division Most of the beneficial insects among these, was in charge of the trapping operations, being tiny or flimsy, rarely fall into the bin. which involved much work at night near the Large Hymenoptera such as a few Scoliids, jungle edge. trapped at times, were set free at the time of taking the catch. Pathological Division Systematic light trapping for the control of Rubber Research Institute of Malaya L. bidentata was attempted only in 1963, the Kuala Lumpur April 1964 earlier work having been exploratory. Though the control achieved was not as complete as REFERENCES with soil insecticidal treatment, it cost only a FROST, S. W. (1953) Response of insects to black and fraction as much and reduced the grub popu- white light. /. econ. Ent. 46, 376. FROST, S. W. (1954) Response of insects to black and lation to a level too low for damage, leaving white light. J. econ. Ent. 47, 275. beneficial insects largely unharmed. Selective FROST, S. W. (1957) The Pennsylvania insect light trap. control is an ideal to be aimed at in all pest J. econ. Ent. 50, 287. control operations. This is especially so in GAUTHIFR, G. (1944) White grub control. 74th Rep. rubber plantations where, though a large ent. Soc. Out. 1943, 26. number of pests exist, both on rubber and on HEIT, C. E. AND HENRY, H. K. (1940) Notes on the species of white grubs present in the Saratoga the ground cover, they are normally held in forest tree nursery. J. For, 38, 944. check by their natural enemies. Trapping KAIRA, A. N. AND KULSHRESHTHA, J. P. (1961) Studies with light therefore is a promising control on the biology and control of / achtiosterna con- measure against this beetle. sanguinea (Blanch.), a pest of -cane in Bihar (India). Bull. ent. Res. 52, 577. ACKNOWLEDGEMENT MAHEUX, G. AND GAUTHIER, G. (1939) The most vul- nerable stage in the life cycle of June beetle. Grateful acknowledgement is made of the 69th Rep. ent. Soc. Ont. 1938, 90. assistance given by Managers and staff of co- OMER-COOPER, J., WHTTNALL, A. B. M. AND FENWICK, operating estates where trapping was conduc- E. M. (1941) The problem of South African turf in relation to invertebrate pests. S. Afr. J. Sri. ted: Tebong Estate (Sites 1 and 4), Kemuning 37, 273. Estate (Site 6) and Tay Swee Joo Estate TASHIRO, H. AND TUTTLE, E. L. (1959) Blacklight as an (Site 3) in Malacca, Regent Estate (Site 2) and attractant to beetles. J. econ. Repah Estate (Site 5) in Negri Sembilan, and Ent. 52, 744. Pengkalan Bukit Estate (Site 7) in Johore. TAYLOR, J. G., ALTMAN, L. B., HOLLINGSWORTH, J. P. AND STANLEY, J. M. (1956) Electric insect traps The writer is indebted to Dr A. Newsam, for survey purposes. U.S. Dept. Agric. ARS Head of the Pathological Division for his 42—3.

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