I Entomology ASSESSMENT OF ALLORHOGAS SP.N. (BRACONIDAE, HYMENOPTERA) AS A BIOLOGICAL CONTROL AGENT OF THE SUGARCANE TOP AND STEM BORERS Djoko Pramono & Boedijono Wirioatmodjo Indonesian Sugar Research Institute (ISRI), Pasuruan - Indonesia ABSTRACT Several experiments were carried out in the laboratory to study the biology of Allorhogas sp.n. (Braconidae, Hymenoptera) and its potency for controlling the sugarcane top and stem borers. Allorhogas sp.n. was found to be a promising biocontrol agent of the sugarcane borer, as indicated by the following attributes: (a) each female was able to parasitise 4 larvae; the average number of maggots laid per host was 21, (b) it was not strictly host specific, (c) it was easy to mass rear, (d) it showed a linear functional response. It preferred to parasitise top borer rather than stem borers. INTRODUCTION The top borer (Tryporyza nivella F.) and stem borers (Chilo auricilius Dudg. and C. sacchariphagus Boj.) are major pests of sugarcane in Burma, Ceylon, China, Formosa, India, Japan, Malaysia, Philippines, Thailand and Indonesia (Williamsl1). Boedijono2 stated that the average rate of infestation of the top borer in Indonesia is 50%, with a sugar loss of about 10%. He also reported that 1 % of joint infestation of the stem borers corresponds to 0.5% sugar loss. To control sugar cane borers, mechanical, chemical and biological means are used. Mechanical controls are very laborious. Insecticides are not effective due to the concealed habit of the borers, especially the top borer. Diatraeophaga striatalis Tns., as a larvae parasite, is used to combat the stem borers. Trichogramma sp., an egg parasite of both top and stem borers, was widely used, but gave inconsistent control. Allorhogas sp.n. (Braconidae, Hymenoptera) has been reported in the literature as a parasite of graminaceous stem borers. The original collection was found in Mexico on May 25, 1981 (Bennett3). Des Vignes5 reported that Allorhogas sp.n. can be reared by using four species of Diatraea in Trinidad. He added that Allorhogas sp.n. was more effective than Apanteles flavipes CAM. and Lixophaga diatraea Tns. In June, 1982, cocoons of Allorhogas sp.n. were received from Pakistan, through the courtesy of CIBC. The present work was undertaken to evaluate the effectiveness of Allorhogas sp.n. as a biological control agent for top and stem borers. I Keywords: Sugarcane, top borer, stem borers, Allorhogas sp.n., biology.
' DJOKO PRAMONO AND BOEDIJONO WIRIOATMODJO 569 MATERIALS AND METHODS Host preferences A pair of adult Allorhogas sp.n. were introduced into wooden-frame cages measuring 20x20~30 cm. Each cage contained ten internodes of sugarcane infested by the borers to be tested. Each experiment was run for one week, after which the parasites were removed. The numbers of parasitised borers, maggots, cocoons and adult parasites were recorded. The preference between the following species was tested: Tryporyza nivella F., Chilo auricilius Dudg., and C. sacchariphagus Boj., using 20 three week old larvae per species. The experiment was replicated three times. Biology Top borers were used as the host of Allorhogas sp.n. to study its biology. The top borer larvae were collected and reared in wooden-framed cages measuring 20x20~30 cm containing 10 internodes of sugarcane. Two larvae of the top borer were allotted to each internode and two wasps were put into each cage. The cages were kept at 24 "C to 27 "C and 70% to 80% relative humidity for one week. The parasites emerging from the parasitised hosts were then reared to the adult stage. To evaluate the effect of food quality on the longevity of adults, five different kinds of food were tried, comprising honey solution in three concentrations (lo%, 15% and 20%), sugar cane and distilled water. Fresh food was provided daily until the adult died. Mass rearing The same kind of cage was used for mass rearing. The cages were grouped according to the following functions. 1. parasitisation of hosts, 2. rearing of parasitised hosts, 3. emergence of adult parasites. Ten internodes of sugarcane containing 20 three week old larvae of the top borer were exposed to five pairs of parasites in the parasitising cage. After one week both parasitised hosts and maggots were collected and transferred to rearing cages where they were kept for one week. The pupae formed were collected and stored in the emergence cages. The adults were kept and were given 20070 honey solution. Distilled water was sprayed in the cages to increase the relative humidity. Functional response The experimental set-up for functional response was similar to the above. The parasite densities used were respectively 4,8,12,16,20, and 24. The host densities were respectively 5,10,15, and 20 larvae of the stem borer. Each experiment was replicated three times. RESULTS AND DISCUSSION Host preferences Tryporyza nivella F. appeared to be preferred as a host over Chilo auricilius Dudgeon and Chilo sacchariphagus Bojer. The relationship between parasite density, the percentage of hosts parasitised and development of parasites in the different host species are presented in Figure 1 and 2 respectively. Those figures show that T. nivella F. was the favoured host
-. L 570 ENTOMOLOGY for Allorhogas sp.n., followed by Chilo auricilius Dudg. and Chilo sacchariphagus Boj. O Tryporyza n~vella Fr Chllo aurlclllus Dudg - 0 Chllo saccharlphagus B paraslte denslty FIGURE 1 Relationship between parasite density and percentage of host parasitized. The fact that Allorhogas sp.n. can be reared on the three species of sugar cane borer, showed that the parasite is rlot strictly host specific. H ~ffaker~,~ states that the most successful biological control agents are not "strictly" host specific, but all must have, or must develop, a high preference for the target pest. Biology The adult female parasitised its host in the cane by first piercing the stem with its ovipositor, paralysing the larva, and then ovipositing. The larvae developed as ectoparasites and within five to nine days formed a mass of cocoons within the stem. The adults emerged seven to nine days later. The life duration was 33-39 days. The morphological characteristics of each stadium are summarised in Table I and Figure 3. In the adult, females may be distinguished by their larger size and the presence of an ovipositor. Mated females could produce 18 to 49 eggs with a sex ratio of 21.67% male and 78.33% female. Unmated females produced only male offspring. Table I1 shows that adults fed with honey solution had a longer life span than those fed with distilled water. Doutt6 stated that there is a growing awareness of the essential role of honey in the longevity and fecundity of insects. Honey solution consists of glucose (35%-41%), vitamins, minerals, fructose, sucrose and hormones which could play an important role in the assimilation system (Anon1). The positive effect of honey solution on the longevity and fecundity has been mentioned by Pramono and Boedijonol0 on Encarsia flavoscutellurn Zehntner.
Tryporyza n~vella I --- F Maggot Pupae paraslie dens~ty FIGURE 2. Relationship between parasite density and development of parasite on three species of host.
FIGURE 3. The life cycle of Allorhogas sp. A. the adult female parasitizes its host B. egg laid in front of its host; C. maggot lives as an ect~parasit~; D. mass of cocoon.
DJOKO PRAMONO AND BOEDIJONO WIRIOATMODJO 573 TABLE I The morphological characteristics of Allorhogas sp. n. Average Stadium Size (mm) Colour Life span (day) Egg 0.6-0.7 White 1-2 Larvae 4-7 White yellowish 4-7 Pupae (inside cocoon) 4-7 Yellow brownish 7-9 Adult : Male 2.5-3.5 Yellowish 8 Female 3.5-4.5 Yellowish 14 Kind of food Average adult longevity (day) Male Female No food (control) 7.98 a*) 14.18a*) Distilled water 8.85 a 15.30 a Sugarcane 18.42 b 20.16 b 10% Honey solution 19.57 c 42.50 c 15% Honey solution 21.35 d 45.13 d 20% Honey solution 27.73 e 48.04 e LSD(5%;df=18) = 1.51 02 1.8549 *) Means marked with similar letters are not significantly different. 1 Mass rearing The method of mass rearing is presented schematically in Figure 4. It was simple and easy, and it was possible to get as many as 21 parasite larvae on each hast. Thus the total number of larvae which could be obtained from each cage, containing 20 borer larvae, varied between 120 and 250 parasite larvae depending on the most species used. I Tryporyza nivella F. is difficult to mass rear in the laboratory, therefore Chilo I L auricilius Dudg. is suggested due to the ease of rearing. However, it should be noted that the host should be changed periodically to T, nivella F. This is because selection pressures may lead tp genetic deterioration of mass reared arthropods (Morrison and King9). Such deterioration can mean the loss of behavioural traits, basic to the effectiveness of released natural enemies, thereby jeopardising the success of
574 L ENTOMOLOGY FIGURE 4 Schematic representation of mass rearing Allorhogas sp. Functional response A functional response is defined as the change in the rate of attack per parasite with variation in the host density (Chua and Dyck4). Figure 5 presents graphically a linear f~nctional response which follows the curve of Nicholson's concept. It means that the number of host bodies attacked depends only upon the searching capacity. If that is constant, the number attacked is directly proportional to the density of the attacked species, with the proportion attacked being constant (Huffaker and Messenger8). CONCLUSION Allorhogas sp.n. lives as an ectoparasite on the larvae of the top and stem borers of sugar cane. Its life duration was 33 to 39 days. The longevity of adults can be lengthened by giving a honey solution as food. The results seem to indicate that Allorhogas sp.n. is a promising biocontrol agent of cane borers, especially the top borer, as indicated by the following attributes: (a) each female was able to parasitise 4 larvae; the average number of eggs laid
I DJOKO PRAMONO AND BOEDIJONO WIRIOATMODJO per host was 21, (b) ir was not strictly host specific, (c) it was easy to mass rear, (d) it showed a linear functional response. However, to be able to exploit this parasite in a biological control program more detailed research is required especially on its development, dispersal and survival in the field.
576 ENTOMOLOGY REFERENCES 1. Anon. (1972). Gizi. Departement Kesehatan Republik Indonesia. Direktorat Gizi. Penerbit PT. Dian*Rakyat, Kawasan Industri Pulo Gadung. Jakarta, 125 p. 2. Boedijono, W. (1973). A brief report of the sugarcane pests at present and its control: Berita th. 1973. Nr 1. Indonesia Sugar Experiment Station. Pasuruan-Indonesia, 25 p. 3. Bennett, F.D., Cock, M.J.W. and Diaz, F.A. (1983). Allorhogas sp.n. (Braconids) a potential biological control agent.for graminaceous stem borer from Mexico. Entomology Newsletter No. 14: 9-12. 4. Chua, T.H. and Dyck, V.A. (1982). Assessment of Pseudogonatopus flaviflernur E. & H. (Dryinidae, Hymenoptera) as a biocontrol agent of the rice brown planthopper. Proceedings: International conference on plant protection in the tropics. 1-4 March, 1982. Kuala Lumpur, Malaysia. 253-265. 5. Des Vignes, V.G. (1983). Laboratory competition studies between Allorhogas sp.n. Cotesia (Apanteles) flavipes Cam, and Lixophaga diatraea Tns. exotic parasites which are reared for the biological control of Diatraea sp. on sugarcane in Trinidad. Entomology Newsletter, No. 14: 7-9. 6. Doutt, R.L. (1966). Biological characteristic of entomophagous adults. In. De Bach, P. (1965). Biological control of insect pests and weeds. Reinhold Publishing Crop. New York, 145-167. 7. Huffaker, C.B. (1971). Biological control. Plenum Press. New York-London, 511 p. 8. Huffaker, C.B. and Messenger, P.S. (1976). Theory and practice of biological control. Academic Press, New York-San Francisco-London, 788 p. 9. Morrison, R.K. and King, E.G. (1977). Mass production of natural enemies. In. Ridgway, R.L. and S.B. Vinson (1977). Biological control by augmentation of natural enemies. Plenum Press. New York-London, 183-218. 10. Pramono, D. and Boedijono, W. (1982). Biologi kutu bulu putih (Ceratovacuna lanigera Zehnt.) dan parasitnya (Encarsia flavoscutenurn Zehnt.). Fak. Pertanian-UNIBRAW, Malang. 33-35. 11. Williams, J.R., Metcalfe, J.R., Mungomery, R.W. and Mathes, R. (1969). Pests of sugarcane. Elsevier Publ. Company. Amsterdam-London-New York, 568 p.