Insect parasitoids, such as tachinid flies (Tachinidae), affect the population dynamics of their hosts in both managed and natural systems, 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 endoparasitoids of arthropods (almost exclusively insects) that typically kill their host before pupating 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 tachinid biology and are lacking for many species. Here we present a host record for Zelia tricolor (Coquillett).
The tachinid, Z. tricolor, belongs to the Dexiini (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 Rhabdoscelus obscurus (Boisduval) (Curculionidae) as a host of this species, citing Wray (1950). Wray (1950) cited a record by C. S. Brimley from Wilson, North Carolina, in which Z. tricolor was reared from a larval Rhodobaemus 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 (Curculionidae), 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 species 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 Asteraceae (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 generation 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 cerambycid 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 puparium on 12 May 2008 and was identified as Z. tricolor 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 larvae (n = 479) were identified as D. texanus by Ted C. MacRae (Chesterfield, Missouri) based on Linsley & Chemsak (1995).
This rearing record demonstrates that in nature Z. tricolor overwintered as a larva within an overwintering D. texanus larva. Our specimen had a 5-day pupal time period under lab conditions. We reared only 1 Z. tricolor from 480 overwintering D. 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 incidental parasitism.
A single specimen of Zelia tricolor (Diptera: Tachinidae) fly, was reared from a larval Dectes texanus (Coleoptera: Cerambycidae) overwintering in soybean in southeastern Missouri. This represents the first record of Z. tricolor from D. texanus and the second host record for Z. tricolor. Our specimen of Z. tricolor overwintered as a larva, had a 5-day pupal period, and represented a parasitism rate of 0.2%.