Traps for Collecting Live Euphasiopteryx depleta (Diptera: Tachinidae) at a Sound Source

Abstract

After Wolcott (1940) reported rearing the tachinid Euphasiopteryx depleta (Wied.) from a Scapteriscus mole cricket (Orthoptera: Gryllotalpidae), interest has been shown in using this fly in introductions for the biological control of Scapteriscus. Fowler and Kochalka (1985) reported attracting E. depleta to the synthesized broadcast calls of S. acletus Rehn & Hebard in Paraguay. Using similar synthesizers (Walker 1982), Fowler and Garcia (1987) reported additional captures of E. depleta, and of rearing it from S. acletus, S. vicinus Scudder and S. abbreviatus Scudder. In those studies, attracted female E. depleta were captured with an aerial net over the synthesizer and larvae taken from them were placed on mole crickets to achieve laboratory parasitism. Subsequently, aerial nets were replaced with a sheet of plastic covered with Tanglefoot?, and large numbers of female E. depleta were obtained. However, in the laboratory, often the Tanglefoot would interfere with obtaining larvae, as many were killed in the female's body through asphyxiation, or were gummed and died as they left the female's body. Also, for some laboratory studies, healthy, gravid females were needed, which could not be obtained by sticky trapping. Using flashlights and aerial nets to capture females at sound synthesizers was not highly productive, as E. depleta tended to avoid lighted areas. To overcome these problems, two traps were designed and field tested (Fig. 1). Both traps were inexpensive, consisting of a wire frame, with muslin sides and funnels, which were used to direct flies into the trap. Cardboard baffles mounted on wire were used to hinder fly escape after capture (Fig. 1). The muslin base was built so that the trap could easily fit over a sound synthesizer (Walker 1982) or over a tape player. Trap designs were evaluated by comparison of the numbers of flies caught in each with the numbers caught on sticky traps. In December 1984, three sound synthesizers broadcasting S. vicinus songs were placed in the field in Rio Claro, state of Sao Paulo, Brazil. One synthesizer was fitted with sticky plastic sheeting, and the other two with the two trap designs. After each night, the location of each was switched. Each synthesizer was separated by 30 m from its neighbor. The sticky trap caught 132 flies during 2 weeks of trapping. Trap B, fitted with 5 funnels, of which 4 were lateral, was about 2.5 times as efficient as design A, consisting of only 1 funnel (Fig. 1). Trap B was about a third as efficient as the sticky trap. Field observations indicated that flies alighted on the muslin and walked extensively over the trap's external surface until they were channeled into its interior through the funnels. Many flies departed without ever reaching the trap's interior. This explains why the numbers of female E. depleta caught in the traps were much less than with sticky traps. If large numbers of flies are required, sticky traps should be used. If, however, viable healthy females are required, then trap design B should be used. Sticky traps are recommended for population monitoring. I thank Joao Justi and Madelena Lima Costa for their assistance with the field portion of this project. This study was funded in part by a grant, USDA No. 83-CRSR-2-