NATURAL CONTROL OF DIATRA EA SACCHARA LIS (FABR. 1794) EGGS IN SUGARCANE FIELDS OF SAO PAUL0

Transcription

1 Entomology NATURAL CONTROL OF DIATRA EA SACCHARA LIS (FABR. 1794) EGGS IN SUGARCANE FIELDS OF SAO PAUL0 F. Oscar Teran Centro de f ecnologia Copersucar ABSTRACT Extensive data (from May 1975 to December 1977) was accumulated on the fate of sugarcane horer (Diatraea saccharalis F.) eggs in several commercial cane fields, to determine the rates of natural control. Freshly laid eggs were placed among sugarcane leaves, sirnulating as far as possible, a natural situation. They were checked periodically until their complete maturation or destruction. Results show an average of 76.16% natural control, with differences between locations and years. Predators appeared as the major component of this natural control (63.64%), while parasites take account of only 3.90% of eggs, and the remaining 8.36% is attributed to other causes (possibly adverse climate, mechanical damage, disease, and even sucking predators). Actual rates of parasitism and predation by sucking insects may have been higher as chewing predators destroyed both healthy and parasitized eggs. INTRODUCTION Populations of the sugarcane borer, Diatraea saccharalis (F.) are usually controlled by many natural factors which reduce their rate of increase in sugarcane fields. These natural control agents affect practically all borer stages. The mode of action of some of these factors, especially the larval parasites, have been studied extensively, but other natural control factors have been studied less. Same work done in Louisiana showed borer predators as being very important natural control factors (Negm and a ens ley 3, Charpentier et a1 '1, even more impmtant than larval parasites. It is very difficult to obtain quantitative information on natural control of other borer stages. Studies and written information regarding eggs are almost always concentrated on their parasites, especially Trichogramma. Attempts have been made to use them for biological control of the borer (Metcalfe and ~reniere~). Meanwhile, other natural enemies of borer eggs, especially predators, have been shown to be much more important in Louisiana (Negm and ~ensle~~l.

2 ENTOMOLOGY The need for quantitative information to improve borer population management schemes motivated this study to quantify the role of all natural control components of borer eggs, under commercial canefield conditions. EXPERIMENTAL PROCEDURE Fresh borer egg masses obtained from mass rearing were used. Egg masses were obtained from insectaries located in Sao Jose and Barra Grande Mills and from those of Copersucar's experiment stations located in Jau and Piracicaba. Egg masses were conditioned on paper strips. These are paper pieces with 2 to 4 eggs masses, marked with a circle and with a number indicating the total eggs in each mass, as shown in Fig. 1. Details of these paper strips were recorded in special blank forms prepared for this study. These records allowed identification of eggs masses that may have been completely destroyed by chewing predators. The paper strips were attached to cane leaves to simulate natural oviposition (Fig. 2). These strips were distributed in commercial cane fields. The cane field characteristics were also recorded. FIGURE 1. Egg masses conditioned on FIGURE 2. Paper strips attached to cane paper strips. leaves to stimulate natural oviposition Regular visits were made to determine the fate of the egg masses. If all egg masses of any strip were destroyed, it was removed and the fate of eggs recorded. The other egg masses, still in good condition, were retained in the field until the embryos reached "black head" stage (ready to hatch). At this stage, they were then taken to the insectary and kept until they hatched or until parasite emerged. After a reasonable time all eggs which had not yet yielded borers or parasites were considered to be "non-hatched" or non-viable. Following the above procedure, paper strips were distributed fortnightly in the same cane field of each location.

3 - Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. FIGURE 3. Natural control of parasitized D. saccharalis eggs. R ESU LTS A summary of results is presented in Table 1 and graphically illustrated in Fig. 3. These results show an average 76.16% natural control, without well-defined variations among months. Variations are well marked among the 4 locations (Tables 2 to 5). Since white coloured,strips could affect natural control, some comparative tests were run with egg masses oviposited on white and green paper. Results are shown in Table 6. Table 7 shows results of natural control of borer eggs exposed in plant and ratoon canes. DISCUSSION AND CONCLUSIONS Results in Sao Paulo differ somewhat from those found in Louisiana (Negm and Hensley3). Average egg predation in Sao Paulo was higher and chewing predators destroyed much more eggs than sucking predators, differing from data of

4 TABLE 1. Natural control of Diatraea saccharatis eggs, in the State of Sao Paulo, Brazil. Weighed averages of studies carried out in some sugarcane fields from May 1975 to December Parasitized eggs Preyed ^'=Eggs Non hatched eggs Natural control Month Exposed Exposed masses eggs No. % Chewed Sucked Total % No. % No. % JANUARY FEBRUARY MARCH APRIL MAY JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER TOTAL I 0 r 0 <

5 -, I -: -.*. $1~. TABLE 2. Natural control of borer eggs in cane fields of Sao JosC. Average records from May 1975 to December , Parasitized eggs Preyed Eggs Non hatched eggs Natural control ", Month Exposed Exposed D z masses eggs No. % Chewed Sucked Total % No. % No. % JANUARY $4.86 FEBRUARY MARCH APRIL ;*-" - - MAY " 143" " 7.03" 1316" 83.40" - AUNE " 96" " 9.04" 940" 52:ll" JULY x 345" " 9.01" 2453" 85.65" AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER n 9 n -I TOTAL X 1645" "

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8 F. OSCAR TERAN z 03? w 0 c Q) 2 b 8 2 d- n!.- (V '3 0 b I-. r C aj 2 0) I/ +5,%

9 1713 ENTOMOLOGY Negm and Hensley. However, it was observed that some of the "non-hatched" eggs were probably damaged by sucking predators (according to newest experiences on symptoms of preyed eggs). Total preyed eggs could have been higher, especially those caused by sucking predators, than the data show. However, differences still remain when compared with results of Negm and Hensley. Results found by sanford4 in Louisiana are also quite different from those reported here and from those of Negm and Hensley. But, as pointed out by Sanford, his data were taken from an area that had received yearly insecticide applications for 10 or more years. Nevertheless, the high percent of parasitism (40.7%) of borer eggs found by Sanford can probably also found in Sao Paulo, if the action of predators can be eliminated. Residues of parasitized eggs chewed by predators were frequently observed. As many parasitized eggs were probably destroyed by predators, the actual rate of parasitism may have been masked. On the other hand, previous tests in Campos, Rio de Janeiro State, showed results similar to those reported by Negm and Hensley. Two preliminary tests in April 1975, showed 37.29% average predation by chewing predators alone, and no difference was found between eggs located in the interior of cane fields (34.85%) and eggs located outside of cane fields or close to pathways (33.37%). A third test in Campos in December 1975, gave results similar to those in Sao Paulo. It showed an average 64.70% natural control, 50.22% being caused by predators, 4.52% by parasites, and 9.95% by other unknown causes. These tests also showed that natural control was higher in ratoon cane (84.62%) than in plant cane (80.56%). This difference was later confirmed in Sao Paulo (Table 7). Parasitized eggs were found in ratoon cane, while there was a complete absence of parasitized eggs in plant canes. This should be carefully studied in the future. Differences from one location to another and from one period to another were the most striking evidence shown by these studies. These differences are probably quitedecisivefor future success of borer populations, and consequently one of the governing factors responsible for differential infestations found in cane fields. In the light of the data shown in Table 6, it was concluded that white paper does not influence results of natural control. Eggs oviposited on green paper were even more preyed and parasitized than those oviposited on white paper. However, no comparisons were made between eggs on paper and eggs on cane leaves. The major conclusion from this research is that predators appear as the major components of natural control of borer eggs. A few eggs were parasitized by Tricho gramma sp, and another small fraction was destroyed by unknown factors (possibly adverse climate, mechanical injury, diseases, and sucking predators). These figures however, are probably masked by final action of chewing predators, which do not distinguish healthy eggs from those previously parasitized or fed on by sucking predators. These studies are being continued to discover the most important factors causing differences in the natural control of borer eggs.

10 F. OSCAR TERAN 1714 REFERENCES I 1. Charpentier, L. J., W. J. McCormick and R. Mathes (1967),Beneficial arthro- I pods inhabiting sugarcane fields and borer infestations. The Sugar Bull. 45(20) : Metcalfe, J. R. and J. Breniere (1969). Egg parasites (Trjchogramma spp) for control of sugarcane moth borers. In Pests of Sugar Cane, J. R. Williams et a1 (ed), Elsevier Publ. Co., New York, USA. 3. Nehm, A. A. and S. D. Hensley (1972). Role of predaceous arthropods of the sugarcane borer (Diatraea sacchatalis (F) in Louisiana. Proc. ISSCT 14: Sanford, J. W. (1976). Sugarcane borer: seasonal distribution and fate of eggs deposited on sugaraane in Louisiana. J. Georgia Entomol. Soc. 11(4):332- ' CONTROL NATURAL DE HUEVOS DIATRAEA SACCHARALIS (Fabr., 1794) EN CMAVERALES DE SAO PAUL0 F. Oscar Teren RESUMEN Se acumularon muchos datos (desde Mayo-75 hasta Diciembre - 77) sobre sobrevivencia de huevos del barrenador en varios catlaverales comerciales, donde se indujo su control natural. Huevos recien ovipositados se colocaron en el follaje de las caiias, simulando en lo posible una situacion natural. Estas fueron inspeccionadas periodicamente hasta su completa maduracion 6 destrucibn, Los resultados muestran un control natural promedio de-76.16%, con variaciones marcadas entre las distintas localidades y aiios. Estas diferencias parecen decisivas para el futuro exito de las poblaciones del barrenador. Los predatores se presentan como 10s mayores componentes de yste control natural (63.63%), mientras que 10s parasitos toman cuenta solo de 3.90% de 10s huevos, y el restante 8.63% es atribuido a otras causas (talvez clima adverso, dazos mecanicos, enfermedades y hasta predatores succionadoses). Sin embargo, estos datos estan probablemente en mascarados por la accion fina1,de 10s predatores masticadores, quienes no distinguen huevos sanos de aquellos succionadds 6 parasitados. C.!