Journal of Chemical Ecology, Vol. 21, No. I0. 1995

IDENTIFICATION OF AN ATTRACTANT FOR THE CANEBORER Sesamia grisescens WALKER (LEPIDOPTERA: NOCTUIDAE)

C.P.

WHITTLE, I'* R.A.

V1CKERS. I L.S. and E.R.

KUN1ATA, 2 T.E.

BELLAS, I

RUMBO ~

~(SIRO Divisi(m ~[ Ent~mu~h~gy, GPO 1700, Canberra, A. C. T. , Auxtrath~, 'Ramu Sugar Lid., Gusap. PO Box 2183 Lue. P~qma New Guinea (Received September 12, 1994: accepted May 16. 1995) Abstract--The ctmlposition of the sex pheromone of Sesalnia ,t~risescens was investigated using gas chronlat(~graphy, electroantcnnogranas, and field trapping. (Z)-I I-Hexadecenyl acetate and (Z)-I I-hexadecenol were identified in field tests as the major attractants. Trapping trials idcntified a 3:2 blend of these compounds as the most ell~z'ctive bait. Gas chromatograpfiy indicated the presence of fiexadecyl acctale. (Z)-9-hexadeceny] acetate, (Z)-9-hexadecenol, and (E)-I I-hexadecenyl acetate in the pheromone gland, but these compounds had no significant effect on trap catches when added to tile major components. Traps bailed with the maior components in a 1 : I ratio caughl more male moths lhan traps baited with virgin females. Key Words--Caneborer, sugarcane, trapping, electroantennogram, sex pheromone, attractant, Insecta.

INTRODUCTION T h e n o c t u i d b o r e r , S e s a m i a g r i s e s c e n s , h a s b e e n r e c o r d e d f r o m s e a level to 1600 m a b o v e s e a level o n t h e P a p u a N e w G u i n e a ( P N G ) m a i n l a n d a n d offs h o r e i s l a n d s ( S z e n t - I v a n y a n d A r d l e y , 1962; B o u r k e , 1968; A n o n . , 1969; B o u r k e et a l . , 1973). K n o w n h o s t p l a n t s i n c l u d e s u g a r c a n e , S a c c h a r u m officinarum L.; edible "pitpit," Saccharum edule Hassk; wild "pitpit," Saccharum r o b u s m m B r a n d e s a n d J e s w i e t e x G r a s s t ( B o u r k e , 1968; A n o n . , 1969; B o u r k e

*To whom correspondence should be addressed. 1409 (X}984)33119511(XX)*I4(~$07

5(}/(I ,c 1995 Plenum Publishing Corl~ralson

1410

WHITTLE ET AL.

et al., 1973: Young, 1982; Li, 1985); Saccharum spontaneum, Pennisetum purpureum, and Panicum maximum (Young and Kuniata, 1992). S. grisescens is the most important insect pest of sugarcane in the Ramu Valley of Papua-New Guinea. Although the extent of damage varies from year to year, losses are always significant, and in 1987 were estimated at $ A I 0 million (P. Sweet, Ramu Sugar Ltd., personal communication, 1991). Adult females deposit clusters of ca. 120 eggs beneath tightly folded leaf sheaths, from whence newly hatched larvae bore into the cane stems in which they complete their larval development and pupate before emerging as adults. Thus, no immature stage is amenable to control with contact insecticides. The systemic insecticide Furadan has proven ineffective and, so far, attempts at biological control with the larval parasite Cotesia (=Apantales)flavipes (Hymenoptera: Braconidae) have been of limited value. Lack of a suitable means of control, a risk of entry into Australia, and a desire by the Australian Quarantine Inspection Service for an effective means of detecting the presence of S. grisescens led to an attempt to identify the insect's pheromone, which could then be employed in traps for quarantine purposes and be evaluated as a mating disruptant for control. Attractants or pheromones are known for tour Sesamia species. S. cretica is attracted to a mixture of (Z)-9-tetradecenyl acetate (Z9-14 : O A t ) and (Z)-9tetradecenol (Z9-14:OH) (Arsura et al., 1977). These two compounds, together with (Z)-I 1-hexadecenyl acetate (ZI I - 1 6 : O A c ) and (Z)-I l-hexadecenol (Z1116 :OH), have been found in the pheromone gland of S. calamistis (Zagatti et al., 1988). Furthermore, ZI 1 - 1 6 : O A c and ZI 1-16:OH have been found to be components of the pheromone of both S. nonagtqoides (Sreng et al., 1985; Rotundo et al., 1985; Mazomenos, 1989) and S. inferens (Nesbitt et al., 1976: Wu and Cui, 1986; Zhu et al. 1987). It was considered likely that a combination of some or all of these compounds would also be attractive to S. grisescens.

MATERIALS AND METHODS

Insect Material. Pupae were collected from sugar cane at Ramu Sugar Ltd. plantations at Gusap in Papua New Guinea during the first week of August 1991. The male and female pupae (100 of each) were separated and packed in sealed containers, which were hand delivered to quarantine in Canberra, Australia (Whittle et al., t993). The timing of the collection was chosen as an additional precaution against accidental release and establishment of the pest in Australia since it is unlikely that it could survive under the climatic conditions in Canberra at this time of year. Moreover, there are no known host plants in the vicinity of Canberra. Male and female pupae were placed in separate cages in an environment cabinet with a relative humidity of 70-80 % and temperatures of 25 °C and 20°C, respectively, at 12L: 12D. At the beginning of each photophase, emerged adults

CANEBORER A F r R A C T A N T

1411

were collected and held individually in waxed paper cups fitted with clear plastic lids and a feeding tube containing 5% honey solution. At no time were the insects permitted to mate. At the end of the investigation, apart from voucher specimens lodged with the Australian National Insect Collection, all insect material was destroyed. Identification of Pheromone Gland Components. Observation of mating behavior in S. grisescens has shown that the moths become sexually active l hr before dawn (L.S. Kuniata, unpublished data). Ovipositors were excised from 3-day-old female moths 3-4 hr before the onset of photophase. The ovipositor was placed in a small test tube drawn from 4-mm-ID glass tubing and allowed to stand for 15 min in 15 #1 of hexane (Waters Associates, HPLC grade). The hexane extract (and washings, 5 p.1) was removed with a syringe and injected in 3-/A aliquots into a small glass tube packed with glass beads (60-80 mesh, 250 mg). Hexane was evaporated from each aliquot in a gentle stream of nitrogen (60 sec, 20 ml/min). Pheromone components were then evaporated from the glass beads under helium (5 ml/min) at 135°C for 10 min, and the effluent was trapped in a cooled (Dry Ice) glass capillary connected by glass-lined stainless steel tubing and PTFE sleeve. The trapped volatiles were washed from the capillary by injecting and then recovering a bead of hexane (2 x 10 ~1). A reference mixture of normal hydrocarbons (Cts, Cl,~, C2o, C22, C24; or Ci7, Cl~, C2~, C_,3; 10 ng/component) was added. The mixture was then examined by gas chromatography using Varian 3300 and Carlo Erba HRGC 5300 instruments fitted with splitless injectors and capillary columns (SGE BP20, polyethylene glycol, bonded phase 1.0 /xm, 25 m x 0.32 mm, 170°C and SGE BP5, 5% phenyl siloxane, 95% dimethyl siloxane, bonded phase 1.0 gm, 12 m x 0.32 mm, 210°C, respectively; career gas was He). Injections were made at 40°C and isothermal conditions maintained for 4 min (inlet purged after 2 rain). The column oven was then rapidly heated (50°C/min) to the operating temperature (170°C or 210°C) and the remainder of the mn completed isothermally at that temperature. Under these conditions the log/linear relationship between retention time and carbon number still applies and computed Kovats indices are reproducible to +0.3 units (Bellas, 1975; Guardino et al., 1976). Data were collected with a Hewlett Packard HP3392A integrator and a DAPA data system (DAPA Scientific Pty. Ltd., Western Australia). Peaks were assigned by coincidence with those obtained from known compounds. Etectrophysiology. Electroantennogram measurements were carried out as previously described (Rumbo, 1988), with a few small differences. Instead of using a glass electrode to connect to the tip of the antenna, the stump remaining after cutting off a few terminal segments from the tip of the antenna was covered with a conductive gel (Lectrogel, an electrosurgical preparation from Valleytab) and a Ag-AgCI electrode inserted into the gel. Lectrogel was similarly used to cover a slit made in the abdomen of the insect for the ground electrode. Sets of sources containing 10 p.g of Z and E isomers of C~4 and C~6 alkenyl

1412

WHITTLE ET AL.

acetates were tested against the male antennae. A blank source was added to each set and sources within a set were presented at random as prompted by a microcomputer, Each set of sources was presented to the same insect three or four times depending on the life of the antenna. A different insect was used for each set. To compensate for aging effects and varying sensitivity between antennae, the measurements were normalized to an average response of unity. Preparation am/Anal~wis of Baits. All synthetic acetates and alcohols were of >99% purity by gas chromatography and obtained from the Research Institute lot Plant Protection, Wagcningen, The Netherlands, and Shin-Etsu Chemical Co, Ltd., Japan. Synthetic pheromone baits were prepared by dispensing 10 ~1 doses from stock solutions of candidate components onto 20 mm lengths of surgical rubber tubing (4.5 mm ID, 6.5 mm OD), The stock solutions contained the candidate mixture as a 10% v/v solution in toluene. Rubber tubing dosed with 10/~1 of toluene alone provided blanks. The particular compounds or mixtures, together with ratios, arc indicated in Tables I and 3 below. In order to measure the volatiles released from a synthetic pheromone bait, five baits were threaded on a wire and placed in a glass tube through which was passed a stream of nitrogen at 60 ml/min. Volatiles in the nitrogen stream were trapped at the outlet with a small tube packed with glass beads (described above). After a collection time of at least 24 rain, the trapped volatiles were desorbed and analyzed by gas chromatography as described above using an SGE BPI0 column (14% cyanopropytphenyl siloxane, 86% dimethyl sitoxane, bonded phase 0.5 p.m, 12 m x 0.32 mm, 160°C). Field Trials. Field trials were carried out using traps similar in design to the Pherocon 1CP trap (Zoecon Company, Palo Alto, Calitbmia), hereinafter called wing traps. Synthetic pheromone baits were placed centrally on the bases of traps. Virgin female traps were baited with 2- to 3-day-old females obtained from field-collected pupae. They were placed individually in plastic tubes (75 x 26 ram) whose bases and lids had been replaced with fine copper mesh. One such tube was placed centrally on the base of each wing trap. Over the eight days of the trial, there were sufficient females available for a total of 14 trap nights, compared with 40 trap nights for each of the synthetic pheromone blends tested. Field trials were carried out at Ramu Sugar Ltd. plantations at Gusap, Papua New Guinea. In all trails there were five replicates of each treatment, and the treatments were assigned randomly to traps set 10.5 m apart within and between rows of cane at a height of 1.3-t .5 m. Catches were recorded and cleared daily, and all traps were moved forward one position daily. The first trap in each row was at least 10.5 m from the edge of the crop. Representative moths caught at each treatment were retained for species identification. Trial 1, using empirical blends (Table 1 below) was carried out in a 16.1ha plot of variety Cadmus cane between July 25 and August 2, 1991. For trial

1413

CANEBORER ATTRACTANT

2 (Table 3 below), blends were evaluated in a field of variety Q127 cane between September 20 and October 10, 1991. Because of a diminishing population in that field, the trial was reset in another field of the same variety between October 15 and November 4, 1991. In trial 3 (Table 3 below), two blends were compared in a field of H56752 cane between January 1 and March 18, 1992 (trial 3A) and repeated between May 30 and June 8, 1992 (trial 3B). Trial 4 was carried out in fields of Q135 (April 5-June 10, 1993) and Q127 (June l 1-August 10, 1993) cane. No blank or virgin female traps were incorporated in trials 2, 3A, 3B, or 4. In a fifth trial wing traps were compared with more robust plastic delta and Hara traps (Hara Products, Swift Current, Saskatchewan, Canada). All were baited with 1 #1 of a l : l ratio of Z I I - 1 6 : O A c and Z I I - 1 6 : O H and were evaluated in a field of Q127 cane from September 20 to October t0, 1991, Because of diminishing population levels, the trial was moved to another field of the same variety for the period October 15-November 4, 1991. Trap data were subjected to an analysis of variance, and the significance of differences between means determined using Duncan's MRT. Missing values, which occasionally occurred when rats removed baits from some traps, were replaced with the mean catch of the remaining replicates for the night that the bait was missing. Means shown in Table 1 have been back-transformed following a reciprocal transformation of the original data.

RESULTS

Initial field trials were carried out with a range of compounds and mixtures based on known pheromones or attractants tbr Sesamia species. The results are shown in Table 1, Most moths were caught at a 1:1 combination of Z I I 16:OAc and ZI 1-16:OH, although there was no significant difference between mean catch per trap with this bait and at the 3 : l ratio of the same components (P < 0.05). Combinations of Z9-14 : OAc and Z9-14 : OH were generally unattractive, and none of the single-component baits caught any S. grisescens, Over the period of these trials, virgin female traps were put out for a total of 14 trap nights (i.e,, the sum of the number of traps on each night that trapping took place), during which three male S. grisescens were caught, for a mean of 0.2 males/trap/night. On the same nights, two synthetic blends, 3:1 and 1 : 1 ratios of ZI 1-16:OAc and ZI l - 1 6 : O H , caught 0.5 and 0.4 males/trap/night, respectively. There were insufficient data to analyze for differences between these means. Electrophysiological and chemical studies were made to confirm the active components of the pheromone and to determine the ratio of these materials in the sex pheromone gland, Electroantennogram responses from male antennae to

1414

WHtTTLE ET AL.

TABLE I. MEAN CATCH PER TRAP 25 J u t . Y - 2 AUGUST 1991 OF A D U L r

grisescens

Sesamia

AT VARIOUS MIXTURES OF ALKENYL ACETATES AND ALCOHOLS (TRIAL 1 )

Compound(s) Z9 1 4 : O A t Z9 14:OH Z9 14 : O A t / Z 9 - 1 4 : OH

ZII 16:OAt ZI 1 - 1 6 : O H ZI 1-16: OAc/ZI I- 16 :OH

Ratio

19:1 3: I I:I 1:3 I: 19

19:1 3:I I: 1 1: 3 I: 19

Blank "Means not ftfllowed by the same letter are significantly

Mean catch/trap (N = 5)" 0 0 0 2.5b I.Oa 0 0 0 0 1.2a 7.8cd 16.0d 3.6bc 2.3b 0 different (Duncan's MRT. P < 0,05).

compounds of different carbon chain length, double bond position, and isomeric configuration produced significant profiles for tetradecenyl and hexadecenyl acetates (Figure 1). The lower response variability, as indicated by the standard deviations, for the hexadecenyl acetates and the greater response to ZI 1-16 : OAc and E11-16:OAc suggests that one or both of these compounds may be present in the pheromone. The response from Z 9 - 1 4 : O A c is likely to be due to binding to the same active site on the antenna. The gas chromatographic analyses of ovipositor extracts from individual virgin female moths showed peaks coincident with those for the compounds listed in Table 2. The average amount of the major component (Z1 I - 1 6 : O A c ) per gland was 44 ng; however, amounts ranged from 4 to 176 ng. The corresponding alcohol, Z11-16:OH, occurred in significant quantities in all of the extracts examined, although the relative amounts ranged widely (142-2728) about the average value shown in Table 2. The relative amounts of hexadecanol (nl6:OH) were also found to be extremely variable. This compound was not detectable in 18 of 21 analyses, but in one analysis n l 6 : O H was found to be twice as abundant as ZI 1-16:OAc. A small peak consistent with E 1 1 - 1 6 : O A c was observed in four of 21 analyses. Similarly E l l - 1 6 : O H was not usually detectable, but a small peak consistent with this compound was seen in two analyses. Analysis on the BP5 column showed peaks consistent with Z l l 16:OAc, Z11-16:OH, and hexadecyl acetate ( n l 6 : O A c ) as the major com-

CANEBORER ATTRACTANT

14 15

Tetradecenyl Acetates

Hexadecenyl Acetates 2

,,liiiiiijli!

ilia,

rr

(5 < w

~

1

o

O

I

I

I

l

l

l

I

I

I

I

I

z

0

O

t o

l l l l l l l l o o o O o O o o

~

~.~.~.~.~.~-~.~-~.~.~

h'h'h'hh'h'hh'hh'h'

StimulusCompound

Stimulus Com~und

FIG. 1, E l e c t r o a n t e n n o g r a m ( E A G ) r e s p o n s e s of m a l e a n t e n n a e from S. grisescens to tetradecenyl (14-carbon) and h e x a d e c e n y l ( 1 6 - c a r b o n ) acetates. W i t h i n e a c h set, results are n o r m a l i z e d to an a v e r a g e v a l u e of 1.0 and are s h o w n tbr each d o u b l e - b o n d p o s i t i o n and i s o m e r tested. E r r o r bars are + 1,0 SD. R e s p o n s e s not m a r k e d by the s a m e letter are s i g n i f i c a n t l y different ( D u n c a n ' s M R T P < 0.05).

ponents, although on this column E and Z isomers are not resolved. Half of one extract was treated with lithium aluminum hydride, which resulted in the disappearance of the acetate peaks in the gas chromatogram when compared to the untreated half of the extract. The results from the field trial of empirical blends (trial 1, Table 1) sugTABLE 2. COMPOUNDS DETECTED IN PHEROMONt- GLAND OF S. grisescens B',' G L C ON POLYETHYLENE GLYCOL C()LLIMN

Average rclalivc ;.Im()u n|

Componcn| n 16 : OAc Z9-16:OAc El 1-16:OAc ZI I- 16 : OAc n 16 : OH Z 9 - t6 : OH El [ - 1 6 : O H ZI 1- 16 : OH

Kov;.lls index

(N = 21)"

Range ''¢'

+_0.3

206 6 9 1000 122 19 1 953

nd-572 nd-39 nd-112 4-176ng nd-2277 nd-57 nd-I 1 142-2728

2318.2 2348.4 2354.3 2362,6 2404.7 2437.2 2441.8 2449.9

"Values normalized to 1000 for ZI 1-16:OAc 1'rid = not delected, values for ZI 1-16 : OAc given in nanograms.

1416

WHITTLE ET AL.

gested that the optimum ratio of Z 1 1 - 1 6 : O A c to Z 1 1 - 1 6 : O H lies somewhere between 3:1 and 1 : 1, while gland content analysis indicated that the addition of Z9-16 : OAc, Z9-16 : OH, and n 16 : OAc might enhance the attractiveness of the two component mixture. Further trials with the blends shown in Table 3 were undertaken to identify the optimum blend for trapping purposes. A 3 : 2 ratio of Z 1 1 - 1 6 : OAc/ZI 1-16 : OH caught significantly more moths than the 1 : I ratio or the 1 : 1 blend with the addition of minor components (P < 0.05) (trial 2, Table 3). While the addition of the minor components to 3 : 2 and 1 : 1 blends of the major components resulted in fewer moths being caught than were taken at the two-component blends alone (trials 2, 3A, and 3B, Table 3), the differences were not significant. Because of the significant EAG response to El 1 - 1 6 : O A c and the detection of a peak corresponding to this compound in the gas chromatographic analyses of gland components, 3 : 2 blends of ZI I1 6 : O A c / Z I I - 1 6 : O H with and without a small amount of E l l - 1 6 : O A c were compared (trial 4). There was no significant difference between mean catches at the two blends. The ratio of components emitted from baits loaded with a 3 : 2 mixture of Z 1 1 - 1 6 : O A c and Z1 1 - 1 6 : O H was measured daily for 12 days. The emitted ratio was found to average 10:9.1 + 0.8 SD.

TABLE 3. TRIALS 2, 3A, 3B, AND 4"

Compound/s

Mean catch IN = 51

Ratio

Trial 2 ZI 1 - 1 6 : 0 A c / Z I 1- t 6 : O H ZI I - 1 6 : OAc/ZI 1 - 1 6 : O H ZI I- 16 : OAc/ZI I- I 6 : O H / nl6:OAc/Zg-16:OAc/ Z9-16:OH

I:I 3:2

8.6(bt 13.8(a)

9:9:2:0.6;0,2

Trial 3 Z 1 1 - 1 6 : O A c / Z I I- 16:OH

5.61b) A

B

3:2

6.21a)

5.6(a~

6:4:1:0.3:0,1

3.4(a)

3.3(a)

ZI 1-16 :OAc/ZI 1 - 1 6 : O H / n l6 : O A c / Z g - 1 6

: OAc/

Z9-16:OH

Trial 4 Zt 1-16:OAc/ZI 1 16:OH ZI I- 16 : OAc/ZI 1 - 1 6 : O H / El 1-16:OAc

3:2 3:2:0.3

2.2ta) 3.0(;11

"Mean catch of Sesanlia ,~,risescens al various mixtures of Mkenyl acetaleS and alcohols. Wilhin lrials, means nol followed by Ihe same telter are significantly diflerenf (lriaI 2: P < 0.05. Duncan's MRT: trials 3 and 4: P < 0.10, t teslL

CANEBORER ATTRACTANT

1417

In a fifth trial the wing traps were tested against plastic delta traps and Hara traps (using 1:1 Z l l - 1 6 : O A c / Z I I - 1 6 : O H as bait) and mean catches (+SD) of 6.8 (2.1), 4.4 (2.0), and 0.8 (1.3), respectively, were obtained. Mean catch at the wing and delta traps were not significantly different from one another, but both were significantly greater than the mean catch at the Hara traps. In addition to S. grisescens, other moths were occasionally caught in the traps. For all trials involving mixtures of Z11-16: OAc and Z11-16: OH, the species caught were a pyralid, Chilo terenellus Pagenstecher (16), and three noctuids, Sesamia inferens (Walker) (3), a Mythimna sp. (2), and a Hydrillodes sp. (9).

DISCUSSION

The results from the field trials and chemical/electrophysiological investigations are consistent with the presence of ZI 1-16:OAc and Z11-16:OH as the principal components of the sex pheromone of S. grisescens. In this respect S. grisescens is similar to three of the tour Sesamia species for which information is available. S. cretica, which is attracted to a mixture of Z 9 - 1 4 : O A c and Z914:OH is the exception. Although Z 1 1 - 1 6 : O A c is the predominant pheromone component, S. grisescens differs in having a far higher proportion of Z1 l 16:OH compared to the other Sesamia species. The gas chromatographic (GLC) analyses of individual pheromone gland contents suggested that the two major components are produced, on average, in a ratio close to 1 : 1. However there were large differences between individual moths, which indicated that male moths might respond to a range of mixtures, and in the field trials it was tbund that although baits loaded with a 3:2 ratio were the most attractive to male moths, significant catches were also obtained with 1 : 1 and 3 : I blends. The GLC analyses of the effluvia from the 3 : 2 baits showed an OAc-OH ratio of 10:9, close to the average ratio found in the gland and well within the range of values tound in the pheromone glands for individual moths (Table 2). Nevertheless, the best definition of the optimum blend will require a study of the effluvia emitted by calling females, a study that was beyond the scope of the present investigation. The saturated acetate n l 6 : O A c was also identified as a pheromone gland component, but there was no evidence for any biological activity for this compound. Similarly, several compounds present in trace amounts were tentatively identified but, when added to the two principal components, failed to enhance the attractancy of the synthetic blend. This was unexpected, particularly with respect to EI I - 1 6 : O A c , which elicited a very strong electrophysiological response from antennae of male S. grisescens. It may be that S. grisescens needs to discriminate between the Z and E isomers to ensure its reproductive isolation

1418

WHITTLE ET AL.

from a sympatric species. However, if this is so, it would also be expected that the E isomer would have some inhibitory effect. For example, the tortricid Epiphyas postvittana shows strong EAG responses to both El 1-14:OAc and ZI 1-14:OAc. While the E isomer is the major component of the pheromone blend, the Z isomer is not present in the pheromone gland and is inhibitory when mixed with the E isomer at 10% or greater (Rumbo et al., 1993). E1116:OAc was not observed to be inhibitory for S. grisescens, and it is not yet known whether the male moth has separate sensory cells for the Z and E isomers. The observation that the addition of secondary components to a 3 : 2 blend of ZI 1-16:OAc and Z 1 1 - 1 6 : O H had little effect on trap catches, and in fact marginally reduced them in one trial, can be compared with the results of Mazomenos (1989). He reported that while the addition of individual secondary components to the major pheromone component of S. nonagrioides (Z11-16:OAc) reduced male capture, a combination of the major and all secondary components was highly attractive. Although it is possible that further adjustment of ratios or addition of minor components in suitable proportions might provide an improved attractant for S. grisescens, the attractancy of the 3 : 2 blend is sufficient to provide a bait for monitoring purposes. Certainly the synthetic blend was found to be more attractive than a caged virgin female moth. The availability of the synthetic attractant will permit monitoring in Australia for accidental introduction of the pest and allow the natural distribution of the species to be mapped in PNG. Little is currently known about the distribution of S. grisescens and, hence, the climatic extremes across its range are unknown. Using weather data for Ramu Sugar Ltd. plantations at Gusap in Papua New Guinea and for the Australian mainland, a climate matching computer program (CLIMEX; Maywald and Sutherst, 1991) indicates that cane-growing areas in the north of Australia might provide a suitable habitat for S. grisescens, This model wilt be refined when further data on the range of the pest becomes available. The use of the synthetic attractant in monitor traps for either quarantine or survey purposes will require further research. During trapping trials in PNG, other species that were occasionally found in traps included S. inferens, a Mythimna sp., and more often C. terenellus and a Hvdrillodes sp. S. inferens has a distribution that includes New Guinea and has been found to be a pest on sugarcane, but this insect has not been a problem at the Ramu Sugar Ltd. plantations where its population density is very low. A total of three S. inferens were trapped during all trials at Gusap, PNG. In a preliminary trial in Australia the synthetic blend attracted single specimens of a noctuid, Athenis reclusa (Walker), and a geometrid, Petelia medardaria H-Sc. No other moths were trapped, but further trials will be necessary to determine the specificity of the monitor traps in Australia. The use of synthetic attractants in traps to monitor populations of S.

CANEBORER ATTRACTANT

1419

grisescens in P N G m a y h a v e o n l y l i m i t e d v a l u e in pest c o n t r o l s t r a t e g i e s as the pest o c c u r s in s u g a r c a n e in d i s c r e t e g e n e r a t i o n c y c l e s that are readily d e t e r m i n e d by s a m p l i n g e g g a n d larval n u m b e r s . H o w e v e r , t h e r e is p o t e n t i a l for u s e o f a s y n t h e t i c b l e n d as a m a t i n g d i s r u p t a n t , a n d trials are c u r r e n t l y b e i n g p l a n n e d to a s s e s s t h e s u i t a b i l i t y o f a t w o c o m p o n e n t b l e n d f o r t h i s p u r p o s e . C o n t r o l o f S. grisescens m a y a l s o a s s i s t in t h e c o n t a i n m e n t o f t h e w e e v i l b o r e r R h a b d o s c e l u s obscurus B o i s d , t h e l a r v a e o f w h i c h e n t e r c a n e s t a l k s t h r o u g h h o l e s m a d e p r e v i o u s l y by S. grisescens.

Ackmm'ledgments--This research was partially funded by the Australian Centre tor International Agricultural Research (ACIAR Small Grant No, 680) and Ramu Sugar Ltd. The authors thank the Australian Quarantine and Inspection Service and the Bureau of Sugar Experiment Stations for advice. REFERENCES ANON. 1969. Insect pest survey for the year ending 30th June 1967. Papua New Guinea Agric. J. 2 [:49-74. ARSURA, E., CAPIZZI. A., PICCARDI, P,, and SPINELLI, P. 1977. (Z)-9-Tetradecen-l-ol and (Z)-9Tetradecenyl acetate: A potent atmaetant system for male Sesamia cretiea Led. (Lep., Noctuidae). Erperientia 33: 1423-1424~ BFLLAS, T.E. 1975. A computer program for calculating linear and logarithmic retention indices in gas chromatography. Chromalogruphia 8:38-40. BOURKE, T.V. 1968. Further records of insects from S~teeh~trum Q~eillorllm in the Territory of Papua and New Guinea with notes on their potential as pest species. Proe. Int. Soe. Su,ttorCane Teehnol. t3:1418-1423, BOURKE, T.V., FENNER, T.L,, STIBICK, J.N,U, BAKER, G.L., HASSAN, E., O'SULLIVAN, D.F.. and L, C.S. 1973. Insect pest survey for the year ending 3Oth June, 1969. Entomology branch, Department of Agriculture, Stock and Fisheries, Port Moresby. pp. XII + 57. GL!,XRD1NO,X., ALB,*,IGt~S,J,. FIRPO. G.. RODRiGL,r~z-VI~ALS,R.. and GASSIOT. M. 1976. Accuracy in the determination of the Kov~its retention index. Mathematical dead time. J. Chromatogr. 118: 13-22. LJ, C.S. 1985. Sugar cane insect pests with special reference to the moth borers in the Markham valley, Papua New Guinea. Mushi 50:13-18. MAyWALD, G,F., and StITHERST. R.W. 199I. Users guide to CLIMEX. A computer program tbr comparing climates in ecology. CS1RO Division of Entomology Report No. 48~ 2rid ed. 5I pp. MAZOMENOS, B.E. 1989. Sex pheromone components of corn stalk borer Sesamia nonagrioides (Lef.). Isolation, identification and field tests. J. Chem. Ecol. 15:1241-1247. NESBIXT, B.F., BEEVOR, P.S., HALL, D.R., LESTER, R., and Dyer