■ Tachinids of Bertha Armyworm
Winthemia head Winthemia body Winthemia
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Reared specimens examined. Winthemia quadripustulata (Fabricius): A series of five adults reared from bertha armyworm collected from Asquith, Saskatchewan on 20 August 1979 (SRCS).

Winthemia is a taxonomically difficult genus of common tachinids with 27 species recognized in the Nearctic region (Wood 1987). The species of America north of Mexico were revised by Guimarães (1972) and a revised key to females was published shortly thereafter by Sabrosky (1973). The keys of these authors improve greatly our ability to identify Winthemia species but they are not completely reliable because certain species are very similar and their intraspecific variation overlaps to some extent with their interspecific differences.

Winthemia rufopicta (Bigot) has been recorded from bertha armyworm in Manitoba by Wylie (1979) and Turnock (1984), and in British Columbia by Guimarães (1972). Winthemia quadripustulata (Fabricius) has been recorded from bertha armyworm in Manitoba by Turnock 1984). Probably the parasitism of bertha armyworm by Winthemia is uncommon and generally occurs only during bertha armyworm outbreaks (Wylie 1979). Winthemia quadripustulata is a Holarctic species recorded from Mamestra brassicae in the Palearctic region (Herting 1960, Turnock 1984).

Recognition. Winthemia is readily distinguished by eye haired, parafacial with hairs on upper half or more, facial ridge with hairs confined to area immediately above vibrissa, prosternum haired, first postsutural supra-alar seta at least as long and stout as first postsutural dorsocentral seta, middle basal seta of postpronotum displaced anterolaterally and forming a triangle with outer and inner basal setae, katepimeron haired, katepisternum usually with 2 setae, and abdominal tergites 3 and 4 with hairs recumbent.

Winthemia rufopicta and W. quadripustulata have prosternum with fine hairs only, 4 postsutural dorsocentral setae, and very narrowed vertex in male (0.20 head width or less). Winthemia rufopicta is further characterized in most specimens by mid tibia bearing 1 stout anterodorsal seta near middle, abdominal tergite 3 without median marginal setae, and male with hind tibia thickly and evenly ciliate. Winthemia quadripustulata is further characterized in most specimens by mid tibia bearing 1 stout anterodorsal seta near middle and 1 or 2 smaller setae above it, abdominal tergite 3 with more than 1 pair of median marginal setae, and male with hind tibia evenly ciliate and often with a longer seta near middle. Typical length for both species is 7-12 mm. The keys by Guimarães (1972) and Sabrosky (1973) should also be consulted.

The puparium of W. quadripustulata (?correctly identified) was described and illustrated by Greene (1922); the puparium of Winthemia sp. was described and illustrated by Guimarães (1972).

Biology. Adult females belonging to the Winthemiini, like those of the Exoristini, do not incubate eggs internally. Hence, eggs are laid directly on a host and do not hatch for some days. Females inevitably choose older host larvae upon which to deposit eggs, presumably as an adaptation to avoid having their eggs cast off during the frequent molts of younger host larvae (Guimarães 1972). According to the investigations of Schaffner and Griswold (1934) in northeastern United States, W. ?quadripustulata is active in the adult stage from May to September, has 2 generations per year, 1 or 2 larvae develop per host, and overwinter as fully developed 3rd instars in the soil. Schaffner and Griswold (1934) record the following differences for W. rufopicta: 2, possibly 3 generations per year, and 1-10 larvae develop per host. Larvae leave the host to pupate (Guimarães 1972). Danks (1975a, 1975b) reports that W. rufopicta in North Carolina is active from April to October, can complete development from egg to adult in less than three weeks on Heliothis species under optimum conditions, and could potentially have up to seven generations per year.

The following serves as a good summary of host range in the genus: "The hosts of Winthemia species in the Nearctic region are listed mostly as armyworms, larvae of other noctuid moths, and to a lesser extent larvae of Sphingidae and Geometridae, many of which are major or minor pests of alfalfa, tobacco, grass, or are defoliators of forest trees" (Guimarães 1972: 28). Arnaud (1978) cites a long list of hosts for W. quadripustulata but according to Guimarães (1972) many records published under this name were based on misidentifications of W. rufopicta. For this reason it is not clear what host W. quadripustulata most commonly parasitizes. The most cited host of W. rufopicta is the armyworm, Pseudaletia unipuncta (Haworth) (Guimarães 1972, Arnaud 1978).

Distribution. Winthemia rufopicta is found throughout North America (Guimarães 1972). Winthemia quadripustulata has three morphological forms with an overall distribution encompassing southern Canada and northern United States, south to California in the west and south to Kansas and Arkansas in central United States (Guimarães 1972).