Distribution ofEumicrosoma benefica(Hymenoptera: Scelionidae) in Southern Chinch Bug (Hemiptera: Blissidae) Populations

Abstract

St. Augustinegrass, Stenotaphrum secundatum (Walter) Kuntze, is a widely used turfgrass in tropical and subtropical climatic regions (Sauer 1972). It is a commonly grown residential turfgrass species in the southern United States, covering 400,000 ha and accounting for 85% of the sod industry in Florida with an estimated value of $262 million (Haydu et al. 2005). The southern chinch bug, Blissus insularis Barber (Hemiptera: Blissidae), is the most serious insect pest of St. Augustinegrass (Crocker 1993). Management of this insect has been challenged by its development of resistance to several key insecticides (Reinert & Portier 1983; Cherry & Nagata 2005, 2007) and overcoming host plant resistance (Busey & Center 1987; Rangasamy et al. 2006). The egg parasite Eumicrosoma benefica Gahan is the only known parasite of southern chinch bugs in Florida. Reinert (1972) first noted the parasite on southern chinch bugs in Florida and noted various aspects of its biology. In a later study of the natural enemy complex of Florida chinch bugs, Reinert (1978) again noted that E. benefica was the only parasite found. These previous studies provided information on the biology of the parasite, but did not provide a large scale survey of the overall distribution or parasitism rates of the parasite in chinch bug populations in Florida. McColloch & Yuasa (1915) reported the E. benefica was an important factor in the control of the chinch bug B. leucopterus (Say) in Kansas. More recently, Wright & Danielson (1992) reported that the wasp parasitized large numbers of eggs of B. leucopterus in Nebraska. Because of the potential importance of E. benefica, the objective of this study was to better understand the impact of the parasite on southern chinch bug populations in Florida. Parasite samples were obtained from 3 contiguous counties (Palm Beach, Martin, and St. Lucie) located in the heavily urbanized southeastern coast of Florida. St. Augustinegrass is commonly used here and the chinch bugs have year round activity (Reinert 1972) because of the climate. Samples were taken for a 1-year period starting Jan 2009. Each 2 months, 1 different infestation was sampled in each county. Chinch bug infestations were located by driving in urban areas and looking for chinch bug damage (i.e., dead or yellow patches of St. Augustinegrass). The presence of chinch bugs (adults and nymphs) was then verified by visual examination for the insects in the grass. Chinch bug eggs are often found in crevices at the grass node or hidden between overlapping grass sheaths on St. Augustinegrass stolons (Nagata & Cherry 1999). These stolons are horizontally growing stems that root at nodes and vary in length e.g., similar to strawberry runners. Ten 50cm St. Augustinegrass stolons were cut and bagged at each location. These clippings were taken to a laboratory where they were cut by hand with scissors and washed through a series of sieves with eggs being caught in the smallest sieve (U.S.A. Standard Testing Sieve #325, 45 micrometer opening) made by Fisher Scientific Company, U.S.A. A microscope was used to find eggs in the sieve which were identified as southern chinch bug eggs based on Vittum et al. (1999). Eggs were placed in vials (1 egg/vial) on a small piece of moistened paper and stored at 25°C. Eggs were examined microscopically each 2-3 d for chinch bug or parasite emergence for 30 d. McColloch (1914) reported that the average length of life cycle of E. benefica ranged from 10 to 28 d depending on temperature. Parasites emerging were stored in alcohol for later species and sex identification. Sex identification of E. benefica was determined based on descriptions of Gahan