Austral Entomology (2018) ••, ••–•• Host plants and habitats of Helicoverpa punctigera and H. armigera (Lepidoptera: Noctuidae) in inland Australia Peter C Gregg,1* Alice P Del Socorro,1 Kristian Le Mottee,1 Colin R Tann,2 Gary P Fitt3 and Myron P Zalucki4 1School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia. 2Agriculture Flagship, CSIRO, Narrabri, NSW 2390, Australia. 3Health and Biosecurity, CSIRO, Dutton Park, QLD 4102, Australia. 4School of Biological Sciences, University of Queensland, Brisbane, QLD 4072, Australia. Abstract For Helicoverpa punctigera (Wallengren), and to a lesser extent Helicoverpa armigera (Hübner), native host plants in non-cropping regions of inland Australia are believed to be contributors to populations which migrate in spring to infest cropping regions of south-east Australia, and southwestern Australia. Non-crop hosts were sam- pled using sweep nets in 71 survey trips in 19 years between 1987 and 2017 for larvae of H. punctigera and H. armigera, over about 2.4 million km2 in inland Australia. Of 1976 samples, H. punctigera larvae were present in 50.5%, distributed throughout the study area. Larvae were found on 106 host plant species in 24 families, in- cluding 61 new host records. H. armigera larvae were found on 33 plant species from eight families, including 14 new host records. However, only 4.3% of samples were positive for this species, and they were mostly in the east of the study area and had fewer larvae than the positive H. punctigera samples. H. punctigera larvae were found in each of six habitats, being, in order of mean numbers per sample: sandy deserts > floodplains > mulga, grasslands and saltbush > stony downs. Host status was determined for both species by plotting relative incidence against relative abundance, and the good hosts for H. punctigera differed between habitats. We discuss the value and limitations of this approach for identifying key hosts in broad scale population dynamics, and primary hosts which may have close co-evolutionary histories with the insects. Key words Helicoverpa armigera, Helicoverpa punctigera, habitats, host plants, inland Australia, migration. INTRODUCTION immigrations can sometimes be correlated with inland rainfall (Oertel et al. 1999, but see also Baker et al.2011). The larvae of moths in the subfamily Heliothinae affect many Zalucki et al. (1994) described host plants recorded in north- crops around the world (Sharma 2005). In Australia, western New South Wales and western Queensland between Helicoverpa punctigera (Wallengren) and Helicoverpa 1987 and 1990. A total of 554 sweep net samples were made armigera (Hübner) are significant pests of cotton, oilseeds, grain at 401 sites, on 96 potential host plants. H. punctigera larvae legumes, vegetables and (for H. armigera only) corn and sor- were recovered from 47 plant species of which 45 were new host ghum (Zalucki et al. 1986; Fitt 1989). Helicoverpa armigera is records. For H. armigera, larvae were recovered from 28 plant cosmopolitan, including recent incursions to South and North species, of which 25 were new host records. We add to these re- America (Kriticos et al.2015).Helicoverpa punctigera is cords new data from inland surveys conducted from 1991 to endemic to Australia, and its distribution is restricted to the 1994, in 1997, 2000, and from 2009 to 2017. The range of sam- Australasian region (Matthews 1999). Both species are pling is extended to the south and west of the original study area, highly polyphagous (Zalucki et al. 1986; Zalucki et al.1994; and data from an additional 1413 sweep net samples are Cunningham & Zalucki 2014) and highly migratory (Daly & included. Gregg 1985; Farrow & Daly 1987; Gregg 1995). Zalucki et al. (1994) introduced the concept of assessing For H. punctigera, native host plants in non-cropping regions host status using a matrix of relative abundance plotted of inland Australia are believed to be key contributors to popula- against relative incidence (Fig. 1). Here, we critically evaluate tions which migrate in spring to infest cropping regions of south- this approach, and apply it to identify important host plants in east Australia (Gregg et al. 1993, 1995, 2001) and southwestern six distinct habitats for H. punctigera in inland Australia. We Australia (Walden 1995). Rainfall, especially in autumn and assess the importance of each of these habitats in the winter, determines the extent of these hosts and the size of spring continental-scale population dynamics of H. punctigera.The data from Zalucki et al. (1994) are included in these analyses *[email protected] for completeness. © 2018 Australian Entomological Society doi: 10.1111/aen.12349 2 P C Gregg et al. parts of the Northern Territory and eastern parts of Western Australia (Fig. 2). This region has almost no crops, and the veg- etation is dominated by native species. The area is arid or semi- arid, and rainfall is extremely variable (Morton et al.2011). While there is a tendency for summer rainfall to be more preva- lent in the north and winter rainfall in the south substantial falls can occur at any time, though many months or even years can pass between significant falls in some areas. We identified six broad vegetation/landform classifications (‘habitats’; Fig. 2), drawing on those described by Morton et al. (2011): (1) sandy deserts, including sand dune/clay pan systems and spinifex plains; (2) floodplains, riparian areas subject to ir- regular inundation that were at least 500 m wide, smaller inun- dated areas being described as creek lines and samples from Fig. 1. Matrix for host plant status, after Zalucki et al. (1994). Rel- them allocated to the habitat in which they occurred; (3) mulga ative incidence is the proportion of samples positive, relative to the (Acacia shrublands), dominated by trees or tall shrubs in the ge- most frequently utilised host. Relative abundance is the mean num- nus Acacia; (4) grasslands, sparsely timbered habitats dominated ber of larvae per sample (positive samples only), relative to the host by grasses; (5) saltbush (chenopod shrublands), dominated by with the highest mean numbers. chenopods especially Atriplex spp. and Maireana spp.; and (6) stony downs, flat to undulating habitats characterised by large areas of bare rock with patches of short grasses, succulents and MATERIALS AND METHODS chenopods. Regions in which the six habitats were most commonly Study area and survey trips found are shown in Figure 2, but in many areas, there was The study area consisted of approximately 2.4 million km2 in in- a fine-grained mosaic of different habitats. Sandy deserts land Australia, encompassing western parts of New South Wales were mostly located in the centre and west of the study area and Queensland, northern parts of South Australia, southern and included the Simpson and Great Victoria deserts. They Fig. 2. Study area showing regions in which the six habitats were most commonly found. © 2018 Australian Entomological Society Ecology of Helicoverpa spp. in inland Australia 3 supported host plants both on the dunes and in clay pans be- study area, and these have been omitted from the analyses re- tween dunes. The dominant vegetation was usually spinifex ported here. Most trips were made between March and Novem- grasses (Triodia spp.) along with Acacia spp. and other pe- ber, with only two (1991 and 1993) in January, and none in rennial shrubs. Floodplains, occupying the smallest area of February. any habitat, were located in the eastern and central regions. They were dominated by grasses and legumes, and included Sampling methods the Darling, Paroo, Warrego and Bulloo Rivers, which drain to the Murray–Darling basin in the east. These eastern flood- Sweep net sampling as described by Zalucki et al. (1994) was plains were usually narrower than those of the Diamantina used. On each field trip, roads and tracks in inland regions were River and the Barcoo–Thomson–Cooper and Eyre–Georgina traversed and when a patch or patches of potential hosts suitable systems, which drain internally to the Lake Eyre basin in for sweep netting (total area >150 m2 and pure enough to avoid the centre. Mulga habitats were located mostly in the east contamination of samples by larvae from intermingled plants), and northwest, with only scattered patches in the centre. They 100 or 200 sweeps were made in replicates of 20 sweeps with were dominated by Acacia spp., often but not always mulga a 38 cm net. On a few occasions when host patches were small, (A. aneura F. Muell. ex Benth.), and supported a diverse fewer sets of 20 sweeps were made. range of hosts between and under the Acacia shrubs. Grass- The latitude and longitude of the sample sites was recorded lands were most extensive in the northeast of the study area using GPS from 1993, and for earlier trips by vehicle odometer (the Mitchell grass plains of central and western Queensland, readings from known locations. Sites were allocated to one of dominated by Astrebla spp.), but patches dominated by other the six habitat classifications with the aid of digital georeferenced grass species occurred elsewhere. Stony downs were undulat- vegetation maps published by various State authorities. For ex- ing to flat areas found mostly in central regions, often ample in New South Wales, we used the Vegetation Classes of forming a mosaic with sandy deserts and mulga. They sup- NSW map (Keith & Simpson 2012). A sample of larvae (at least ported mostly short grasses, succulents and perennial cheno- 12, or all those collected if the total catch was less than 12) was pods. While chenopods were common in most habitats, they reared on artificial diet (Teakle & Jensen 1991) to confirm iden- dominated the plains in the southern parts of the study area, tification. Larval densities were calculated by multiplying the to- western New South Wales and South Australia, making up tal catch per 100 sweeps by the proportion of surviving larvae the saltbush habitat, with Medicago spp.