(TACHINIDAE: DIPTERA) 1. J.P. Roth2 and E.G. King3

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1 Entomology LARVPOSTONAL CYCLE OF LXOPHAGA DATRAEAE (TACHNDAE: DPTERA) 1 J.P. Roth2 and E.G. King3 ABSTRACT Larviposition by the tachinid Lixophaga diatraeae (Townsend) on methanol extracts of frass from Diafraea saccharalis (F.) larvae fed sugarcane began on the 7th day after female emergence from puparia and mating, peaked during the 8th to 14th day, and declined thereafter. Over 90% of the total number of maggots deposited were deposited by the 15th day. Life span of the female flies ranged from 8 to 23 days and averaged 17.5; therefore, mortality was not a significant factor in limiting larviposition. Flies 14 days or older behaved differently than younger flies larvipositing more readily near frass or other dead flies with little delay between maggot depositions. NTRODUCTON A large-scale rearing program was developed for production of the tachinid Lixophaga diatraeae (Townsend) on larvae of Diatraea saccharalis (F.) for testing the feasibility of using L. diatraeae in periodic releases for control of D. saccharalis4. L. diatraeae is a larviparous tachinid, native to several of the Caribbean Sea islands, that has been colonized in other areas, including Louisiana1 and inore recently Floridas. Van Whervin6 reported that the gestation period of female L. diatraeae was 7-8 days after mating. King and Martin3 conducted a study where L. diatraeae were serially dissected daily after mating. They found that eggs occurred in the fly uterus within 24 h alter mating and the embryonic period was about 5 days at 26OC. Further, the number of hatchable parasite maggots in a fly uterus peaked at 78/fly after 12 days. Thereafter, the maggot number decreased apparently due to random larviposition by the fly to release pressure of the maggots in the uterus as reported for similar Study conducted by first author in partial fulfillment of the requirements for the Doctor of Philosophy degree in Entomology at Mississippi State Univ., Mississippi State 39762, and in cooperation with the Delta Branch of the Mississippi Agric. and Forestry Exp. Stn., Stoneville (2) Present address, Department of Entomology, Mississippi State Univ., Mississippi State (3) Research Entomologist, Bioenvironmental nsect Control Laboratory, Agric. Res. Serv., USDA, Stoneville, Mississippi

2 ENTOMOLOGY tachinids by Clausen2. The study reported here was made to define the period in which female parasites were responsive to the larviposition stimulant in the host frass and to determine what influence parasite age had on this response. This information was needed in rearing of this parasite, timing of parasite releases, and in the development of bioassay procedures for isolating and identifying the substances in the host frass stimulating larviposition. MATERALS AND METHODS Mated female flies were held in aluminum frame cages (25 x 23 x 15 cm) covered with a double layer of 'seamless tubular gauze. They were obtained by removing pairs in the act of copulation and transferring 15 pairs to each of 4 holding cages. Male flies were removed from the holding cages 2 days later. Food was provided by sprinkling unrefined brown sugar on top of the cage covering immediately after flies were placed in the cages and at intervals thereafter. A 480-ml jar containing distilled water and 2 paper towels was placed inside each cage, and cages were lightly sprinkled 2-3 times daily with distilled water so the flies would have an additional source of moisture. The flies were held at 28OC and % RH with 14 h light and 10 h dark. Preliminary studies had shown that methanol extracts of frass from D. saccharalis larvae fed sugarcane plants was a highly effective larviposition stimulant. Thus fly larviposition was measured- by exposing them to the methanol extracts. A green wax candle with 3 holes (4 mm x 4 mm) bored into one side at 2.5 cm intervals was placed in each cage. A cotton plug saturated with the frass methanol extract was placed in each hole and replaced daily. Maggots in the cotton plugs and on the candles were counted daily with the aid of a binocular microscope. Dead flies; were removed from the cages daily and recorded. These flies were dissected to determine if they contained hatchable maggots. RESULTS The average number of maggots deposited per fly per day peaked during the 8th to 14th day after mating and declined thereafter. The average number of maggots counted per fly was Eighty-seven percent of these maggots were deposited during the peak larviposition period (8-14 days) and only 4% were deposited by 18 day old or older flies. Maximum generation larviposition occurred on day 15 by which time 90% of the expected maggots had been deposited (Table ).

3 J.P. ROTH AND E.G. KNG 541 TABLE. Larviposition and mortality of 60 female Lixophaga diatraeae adults continuously exposed to a larviposition stimulant. Accumulative Accumulative Day after Total number Mean numbera/ % for totalb/ % mating of maggots maggots/fly maggots for gen. mortality a/ Average number of maggots per fly per day (total maggot deposition + total live flies = total maggots per fly). b/ z maggots deposited each day + total number maggots deposited (1051) x 100. The niean life span of female flies was days ranging from 8 to 23 days. Thus most of the flies lived through the peak larviposition period. Dead flies were dissected and all contained hatchable maggots indicating that even with continuous exposure to the larviposition stimulant all maggots are not deposited. The age of the insects had a marked effect on their larviposition behavior. Flies 14 days old or older were much more erratic in their

4 542 ENTOMOLOGY behavior. Older flies tended to be less accurate in the placement of maggots near the frass, would often arviposit repeatedly without a recovery period, and often larviposited on dead flies at the bottom of the cage or randomly on sides of the cage. DSCUSSON These data indicate that L. diatraeae does not begin larvipositing until 6-7 days old, attains peak larviposition between 8-14 days and dies shortly thereafter. Results were similar in the study conducted by King and Martin3. Thus flies should be released in the field when they are 6 to 7 days old, if they are to be released at the start of the larviposition period. We considered the average number of maggots deposited per fly (23.5) as too low and indicative of the inefficiency of the collection method. Many of the maggots apparently escaped from the candle or were overlool$d. Nevertheless, many of the maggots were never deposited remaining in the dead fly's uterus. King et al4 developed a rearing program for L. diatraeae whereby the maggots are extracted from day old flies with a blender. Based on the data in this study as many or more maggots would be obtained by sacrificing day old flies in the blender as would be if they were allowed to larviposit normally. The larviposition behavior of flies over 14 days old was obviously not the norm and may have been the result of lowered stimulus thresholds. This would conform to the behavior of other tachinids under similar conditions as reported by Clausen2 and is evidenced by the fact that King and Martin3 found empty egg sheaths in the uterus of older flies which had not been exposed to larviposition stinlulant. 1. Bennett, F.D: (1969). Tachinid flies as biological control agents for sugarcane moth borers, pp n Pests of Sugarcane, J.R. Williams, J.R. Metcalf, R.W. Mungomery and R. Mathes [ed.), Elsevier Publ. Co., New York. 2. Clausen, C.P. (1940) Entomophagous nsects, McGraw Hill Co. New York, 688 p. 3. King, E.G. and D.F. Martin. (1975). Lixophaga diatradae: Development at different constant temperatures. Environ. Entomol. 4, King, E.G., D.F. Martin and L.R. Miles. (1975) Advances in rearing of Lixophaga diatracae (Tachinidae: Diptera). Entomophaga 20, Summers, T.E., E.G. King, D.F. Martin and R.D. Jackson. (1976). Biological control of Diatruca saccharalis in Florida by periodic releases of Lixophaga diatraeae. Entomophaga (n press). 6. Van Whervin, L.W. (1966). Ecology, biology and behavior of Lixophaga diatraeae Tns. and results of attempts ( ) to establish, it in Barbados for the control of the moth borer, Diatraeae saccharalis (F.). ~ufl, Dept. Sci. Agric., Barbados 43, 38 p.

5 J.P. ROTH AND E.G. KNG 543 CCLO LARVPOSCONAL DE LXOPHAGA DATRAEAE (TACHNDAE: DPTERA) J.P. Roth y E.G. King RESUMEN La larviposicion del taquinido L. diafraeae (Townsend) sobre extractos en metanol de deyecciones de larvas de D. saccharalis (F.) alimentadas con cafia, comenzo el 7.0 dia despues de la emergencia de la hembra, alcanzo su pic0 durante el 8.O al 14.0 dia y declino posteriormente. Mas del 90% del numero total de "maggots" fueron depositados por el 15.O dia. La longevidad de las moscas hembras vario de 8 a 23 dias con promedio de 17.5; por eso, la mortalidad no fue factor significativo en la limitacion de la larviposicion. Las moscas de 14 o mas dias se comportaron diferente de las moscas mas jovenes, larvipositando mas rapidamente cerca de las deyecciones o de otras moscas muertas, con poca demora entre deposiciones de "maggots".