CARIBBEAN FOOD CORPS SOCIETY

SERVING THE CARIBBEAN SINCE 1963 CARIBBEAN FOOD CROPS SOCIETY 39 Thirty Ninth Annual Meeting 2003

Grenada Vol. XXXIX Number 1 Proceedings of the Caribbean Food Crops Society. 39(2):180-146. 2003

MEASURING THE EFFICACY OF THE BIOLOGICAL CONTROL PROGRAM FOR SUGARCANE BORER D1ATRAEA SACCHARAUS (F.) IN BARBADOS: JOINT INFESTATION SURVEYS FOR THE PERIOD 1999-2002

/ 2 1 Litta Paulraj and Ian Gibbs . Caribbean Agricultural Research & Development Institute, P. O. Box 64, Cave Hill Campus, St Michael. 2Ministry of Agriculture & Rural Development, Graeme Hall, Barbados.

ABSTRACT: This paper reviews the biological control program for the sugarcane mothborer (F.) in Barbados over the period 1999-2002. The data for this period were analyzed, fitting infestation level to variety, crop, rainfall zone, and year, assuming a logistic regression model with a Poisson distribution of all main effects (variety, crop, rainfall zone, and year). The results showed that all first order interactions were highly significant (p<0.001) and that the overall joint infestation levels remained below the Economic Threshold Level (ETL) of 5% joints bored. This finding suggests that the pest is continuing to be effectively controlled by its two parasitoids Cotesia flavipes and Lixophaga diatraeae.

INTRODUCTION

The sugarcane moth borer, Diatraea saccharalis (F.) (: Pyralidae: ), is the major pest of sugarcane in Barbados. Gibbs (1995) also listed the types of damage this pest causes to sugarcane plants and the resultant losses in cane quality, amount of extracted juice, percentage sucrose, and purity of the juice. Borer injury can also cause the color of the clarified juices and syrups to darken and their turbidity to increase. Secondary infection by fungi such as Glomerella tucumanensis (Speg.) Arx and Muller, which causes red rot disease, can occur through the holes bored into the stalks and can lead to the inversion of sucrose to glucose. It is generally considered that bored cane does not keep as well as the sound cane after it is cut for milling. Losses caused by the moth borer, therefore, may be divided into field loss and factory loss. Each percentage point of joints bored is considered to lead to a 0.5% loss of sugar yield (Cock 1985 citing Metcalfe, 1969). Moth borer control by pesticide is not a feasible method in Barbados and biological control is considered to be the best and safest control strategy for this pest. Gibbs (1995) reported on the history of the biological control programme for sugarcane moth borer on the island. Prior to 1966, Diatraea saccharalis infestation in Barbados had averaged up to 15.5% joints bored (Alam, 1980). The Caribbean Agricultural Research and Development Institute (CARDI) started rearing in the laboratory the moth borer's major parasitoid Cotesia flavipes (Cam.) (Hymenoptera: Braconidae) in 1994 and releasing it throughout the island, particularly in areas/varieties that had infestation levels greater than the accepted Economic Threshold Level (ETL) of 5% joints bored. The efficacy of this program is monitored by conducting an annual joint infestation survey at harvest time.

143 MATERIALS AND METHODS

The annual joint infestation survey was conducted only on sugarcane that would be cut by machine harvesters. Three-stalk samples were taken every 20 stools from the uncut cane next to the open (harvested) side of each field. Sampling was conducted every 10 rows in order to cover a wide area and a total of 100 stalks per field were checked. The percentage joint infestation was determined as the proportion of joints bored expressed as a percentage of the total joints in the 100 stalks. The field name, sugar cane variety, date of sampling, plantation name, crop (plant cane or ratoon), acreage and rainfall zone were recorded for each sample. Approximately 5% of the total sugarcane acreage is sampled during each annual joint infestation survey.

RESULTS AND DISCUSSION

The crop area occupied by the six major sugarcane varieties grown during the period 1999-2002, compiled by the Agronomy Research & Variety Testing Unit (ARVTU) Barbados Agricultural Management Company Ltd. is presented in Table 1.

Table 1. Percentage of the total crop acreage occupied by the six major varieties grown in 1999- 2002.

Variety Percentage of the total crop acreage for the year 1999 2000 2001 2002 B62163 9.09 7.37 3.51 1.90 B74541 12.69 10.91 11.22 10.30 B77602 22.02 21.61 24.19 21.28 B80251 7.68 8.73 8.86 7.37 B80689 10.31 9.30 12.04 11.90 B82238 16.20 17.85 20.04 23.06

The average yearly percentage joint infestation by sugarcane mothborer for all varieties over the island during the period 1999 -2002 is shown in Figure 1 (Paulraj, 2002).

181 Figure 1. Sugarcane moth borer percentage joint infestation for 1999-2002.

4.5 ,

4

3.5 xï 3 mM 2.5 % infestation 2

1.5 1

0.5 0 1999 2000 200.1 2002 Year

An Analysis of Variance (ANOVA) was performed,on the data for this period (1999-2002), fitting infestation level to variety, crop, rainfall zone and year, assuming a logistic regression model with a Poisson distribution of all main effects (variety, crop, rainfall zone and year). The results showed that all first order interactions were highly significant (p<0.001). The mean percentage joint infestation levels in the various crop stages of the major varieties during the same period are presented in Table 2.

Table 2. Mean percentage joint infestation levels for 1999-2002 in the different crop stages of the six major sugarcane varieties. Variety Percentage joint infestation in crop stage Plant canç ratoo——n 2^ratoon 3 ratoo•n- ratoon B62163 2.32 (5)* 2.77 (7) 1.92,(11) 1.93 (6) 1.22 (7) B74541 2.99(12) 1.78 (13) 1.56(12) 2.27 (8) 1.22 (6) B77602 3.67 (35) 1.39 (29) 0.88(16) 1.38 (21) 1.19(4) B80251 4.61 (8) 2.61 (3) 1.79(10) 1.43(10) 1.71 (3) B80689 8.14(20) 3.58 (13) 2.91 (14) 1.79 (8) 4.44 (3) B82238 4.81 (24) 2.33 (26) 2.86 (25) 2.44(14) 1.73 (4) *VaIues in parentheses are thç numbers of observations

The joint infestation levels for the six major varieties for high, intermediate and low rainfall zones during the 1999-2002 period are givçn in Table 3.

182 Table 3. Percentage joint infestation of sugarcane moth borer in the major varieties grown in the three rainfall zones for the years 1999-2002. Variety Percentage joint infestation in rainfall zones High Intermediate Low B62163 1.95 (31)* 1.65 (5) 3.93 (1) B74541 2.00(14) 1.98 (35) 2.74 (5) B77602 1.96 (41) 1.73 (37) 2.71 (29) B80251 2.22 (28) 1.93 (3) 4.66 (3) B80689 4.84 (33) 6.03 (16) 5.28(10) Β82238 3.11 (46) 3.03 (33) 2.89 (25) *Values in parentheses are the numbers of observations

Table 4 presents the data collected showing the joint infestation levels in the five crop stages of the six major commercial varieties with respect to rainfall zone.

Table 4. Sugarcane mothborer joint infestation levels in the crop stages of the six commercial varieties, according to rainfall zone. Crop stages Percentage joint infestation in rainfall zones High Intermediate Low Plant cane 4.8 (53)* 4.1 (39) 5.5 (23) 1st ratoon 2.26 (40) 1.8(32) 2.6(19) 2nd ratoon 1.85 (46) 2.02 (21) 1.5 (21) 3ld ratoon 2.14(37) 1.98 (21) 2.8 (9) 4th ratoon 1.35 (14) 2.17 (12) 1.8(1) * Values in parentheses are the numbers of observations

The six major varieties account for 75.8% of the sugarcane planted in Barbados (Table 1). It is thought that these varieties fairly represent the overall situation with respect to mothborer infestation in the entire sugarcane crop grown each year of the period under review. The levels of joint infestation, determined by each annual survey, can be seen in Figure 1. These levels are consistently below the Economic Threshold Level (ETL) of 5% joints bored and suggest that the biological control program is working successfully. Moth borer damage is usually higher in plant cane than in subsequent ratoon crops (Table 2). Gibbs (1996) reported on similar findings for the period 1984-1991 and again for 1996. This phenomenon is probably due to a lack of adequate parasitoid numbers in the plant cane, and also plant cane is in the field for a period of eighteen months before it is harvested. Infestation levels decreased with crop ratoon age and were thought to be a result of increasing parasitoid populations and parasitism rates. In relation to the rainfall zones, percentage infestation of the six varieties was generally higher in the low rainfall zone (Table 3). This was probably due to decreased mortality of moth borer larvae, particularly in the neonatal larval stage before they bore into the stalk. These larvae can be easily washed off the plants by rainfall in the higher rainfall zones and be subjected to prédation by ants and predatory beetles on the ground. Data in Table 4 showed again that infestation levels in plant cane are generally higher than in ratoons, irrespective of rainfall zone.

183 A total of 26,380 C.flavipes wasps were reared in the laboratory and released across the island during the reviewed period. These parasitoids were mainly released in areas/varieties identified by the annual infestation survey as having infestation levels greater than the accepted ETL of 5% joints bored. This distribution was an effort to suppress borer infestation and to build up sufficient parasitoid numbers in these 'hot spots'. Table 5 shows the amounts of sugar and money saved in the years 1999 to 2002 as a result of the biological control program of the two larval parasitoids Cotesia flavipes and Lixophaga diatraeae.

Table 5. Sugar production and the amount of sugar and money saved through the action of the two larval parasitoids C. flavipes and L. diatraeae in Barbados during the period 1999-2002. Year Acreage % Joint Amount sugar Sugar price Amount sugar Amount Bds$ Infestation produced (t) received saved (t)* saved** (Bds$/t) 1999 21,281 3.6 52,317 1,132 3,139 3,553,348 2000 21,541 2.6 58,373 992 3,736 3,706,112 2001 20,834 2.6 49,796 964 3,237 3,120,468 2002 19,648 2.5 44,819 925 2,913 2,694,525 Mean 20,826 2.8 51,326 1003 3,233 3,242,699 *Based on the Joint Infestation level of 15.5% prior to the use of the two parasitoids C. flavipes and L. diatraeae and the reduction of 0.5% sugar yield for every 1.0% joint infestation. **Based on the price received for exported raw sugar.

The data in Table 5 assume that the joint infestation level would have remained at the parasitoid pre-introduction average of 15.5% and that this level would have not been adversely affected by the change in varieties grown since that period. Using these assumptions, the average amount of sugar saved per year for the four-year period would be 3,233 t, which represents an average of Bds$ 3.2 million saved per year as a result of the biological control program.

ACKNOWLEDGEMENTS

We thank the Barbados Agricultural Management Company (BAMC) for funding all four years of the survey. The authors gratefully acknowledge the assistance of Mr. F. Worrell, Technical Assistant, CARDI, for collecting the data. Also, we would like to thank Mr. Harm de Boer and Dr. S. Bellamy, Agronomy Research and Variety Testing Unit (ARVTU) for providing information on plantations and varieties and Mr. B. Lauckner, Biometrician, CARDI for advice on the design and methodology of the survey and for analyzing the survey data.

184 REFERENCIAS

Alam, M.M. 1980. Biological and ecological factors affecting the of sugarcane borer (.Diatraea saccharalis F.) in Barbados. Proceedings of the XVII congress of the international society of sugarcane technologists. Feb 7-11, Manila, Philippines. Vol.2, page 1831- 1842. Cock, M.J.W. 1985. (ed.) A Review of Biological Control of Pests in the Commonwealth Caribbean and Bermuda up to 1982. Commonwealth Institute of Biological Control, Commonwealth Agricultural Bureau, UK. ρ 61. Gibbs, I.H. 1995. Integrated Pest Management of Sugarcane Moth Borer. Report to Β AMC for the period March 1994 to May 1995. Caribbean Agricultural Research and Development Institute, Barbados. 32pp. Gibbs, I.H. 1996. Integrated Pest Management of Sugarcane Moth Borer. Report to the Barbados Agricultural Management Company on the 1996 Sugarcane Crop Moth Borer Joint Infestation Survey. Caribbean Agricultural Research and Development Institute, Barbados. 8pp. Paulraj, L. 2002. Sugarcane mothborer joint infestation survey 2001-2002 crop. A report to Barbados Agricultural Management Company Ltd. by Caribbean Agricultural Research and Development Institute, Barbados. 20pp

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