Zelia tricolor(Diptera: Tachinidae): First Host Record fromDectes texanus(Coleoptera: Cerambycidae)

Abstract

Insect parasitoids, such as tachinid flies (Ta chinidae), affect the population dynamics of their hosts in both managed and natural sys tems, and are a major component of global biodiversity (Smith et al. 2006; Stireman et al. 2006). There are about 10,000 described species of tachinids and probably some thousands more undescribed species (O'Hara 2008). Tachinid species have been used in applied biological control, sometimes with great success (Grenier 1988). All tachinid species are koinobiont endo parasitoids of arthropods (almost exclusively insects) that typically kill their host before pu pating within the remains of the host or leaving the host to pupate elsewhere (Stireman et al. 2006). Most tachinids parasitize the larval stage of their hosts; however, 5-10% of species parasitize adults, and none are known to attack eggs or pupae (Stireman et al. 2006). Host records are the beginning of understanding ta chinid biology and are lacking for many species. Here we present a host record for Zelia tricolor (Coquillett). The tachinid, Z. tricolor, belongs to the Dexi ini (Dexiinae), a tribe that almost exclusively parasitizes beetles. It is widely distributed in North America from Nevada to Pennsylvania, and south to Mexico and Florida (O'Hara & Wood 2004). Arnaud (1978) listed only Rhabdo scelus obscurus (Boisduval) (Curculionidae) as a host of this species, citing Wray (1950). Wray (1950) cited a record by C. S. Brimley from Wil son, North Carolina, in which Z. tricolor was reared from a larval in a Dahlia stem on Aug 30, 1939. Rhabdoscelus obscurus does host tachinids (Waggey & Beardsley 1974), but is known to occur only in the Australasian and Oceanian regions (Halfpapp & Storey 1991). Wray (1950) did not identify the host to species and Arnaud (1978) assumed it to be R. obscurus, but it is more likely that the Rhodobaemus of Wray is Rhodobaenus (Cur culionidae), of which 2 species occur in North Carolina: R. tredecimpunctatus (Illiger) and R. quinquepunctatus (Say) according to the insect collection at North Carolina State University (NCSU 2010). Both of these Rhodobaenus spe cies feed on Asteraceae (Blatchley & Leng 1916) and are likely to be found in Dahlia. Therefore, the previously known host for Z. tricolor should be correctly stated as Rhodobaenus sp. Dectes texanus LeConte, is a wide-ranging North American cerambycid that primarily feeds on herbaceous plants in the family Aster aceae (Lingafelter 2007) and can be a pest of sunflower (Helianthus annuus L.) (Rogers 1977). It was first reported as a pest of soybeans (Glycine max (L.) Merr.) in 1968 in Beaufort County, North Carolina (Falter 1969) and in New Madrid and Dunklin Counties, Missouri (Hatchett et al. 1973). Dectes texanus has 1 gen eration per year (Falter 1969; Hatchett et al. 1975), and partially grown larvae overwinter inside the stem of the host plant (Hatchett et al. 1975). Several species of Hymenoptera in the Braconidae, Ichneumonidae, and Pteromalidae are known to parasitize D. texanus in Ambrosia (Hatchett et al. 1975); however, there are no published records of parasitoids of D. texanus from soybeans (Niide 2009). On 7 May 2008, a puparium of a larva was found that had emerged from a D. texanus larva. The D. texanus larva was part of a cohort of cer ambycid larvae from the 2007-growing season taken from soybean stems in Southeast Missouri during late-winter 2008 and reared on artificial diet (Hatchett et al. 1973, Product #F9703B, Bio Serv, Frenchtown, NJ) in an insect rearing room (16:8,24?C). The adult fly eclosed from the pupar ium on 12 May 2008 and was identified as Z. tri color by Norman E. Woodley of the Systematic Entomology Laboratory, Agricultural Research Service, U.S. Department of Agriculture (Lot# 0806898). The specimen currently resides in the University of Missouri Enns Museum collection (Columbia, Missouri). The remaining individuals of the aforementioned cohort of cerambycid lar vae (n = 479) were identified as D. texanus by Ted C. MacRae (Chesterfield, Missouri) based on Lin sley & Chemsak (1995). This rearing record demonstrates that in na ture Z. tricolor overwintered as a larva within an overwintering D. texanus larva. Our speci men had a 5-day pupal time period under lab conditions. We reared only 1Z. tricolor from 480 overwintering!), texanus larvae, representing a parasitism rate of 0.2%. Additional work is needed to determine the parasitism rate of Z. tricolor in other populations of D. texanus and what role it may play in D. texanus population dynamics or if this report was a case of an inci dental parasitism.