Montana Field Guide

Genus Aphthona: Front carinate, frontal tubercles well developed and clearly marginated, antennae longer than half the body length, prothorax broader than long, pronotum lacking both longitudinal and transverse grooves, elytra wider at base than pronotum, elytral punctation confused or (sometimes) in irregular rows, procoxal cavities open, tibial spurs simple and inserted at outer corner of tibia, first hind tarsi usually distinctly shorter than 1/2 length of hind tibia. Male with first segment of front tarsus enlarged (not enlarged in female), posterior margin of last visible abdominal sternite distinctly lobate (evenly rounded in female), males smaller and more slender on average than females; female antennae proportionally shorter (LeSage and Paquin 1996).

Aphthona lacertosa: adults about 3.0-4.0 mm in body length; dorsal and ventral body surfaces black with strong blue metallic reflections (occasionally dark green); hind femora partly brown, tibia yellowish with small dark area on dorsal surface; tip of male aedeagus nipple-shaped; female receptacle ovoid, dorsal surface of recepticle convex; female styli elongate, 10X as long as wide (Gassmann et al. 1996; LeSage and Paquin 1996; Rees et al. 1996).

Adults emerge late May through July, eggs throughout mid-June to August, larvae fall to spring of following year, pupae late spring to early summer (Gassmann et al. 1996; Rees et al. 1996; Lajeunesse et al. 1997; Skinner et al. 2004, 2006; Lym 2005; Joshi 2008).

See General Description (above) for distinguishing Aphthona from other beetles. A. lacertosa differs from A. nigriscutis externally by having an overall black appearance (except the legs) with metallic blue to dark green reflections of the body instead of being brown with a contrasting black dot behind the thorax at the leading edge of the wings.

Not described; apparently non-migratory. Dispersal rare in Alberta between release plots and non-release plots 100-200 m apart and imbedded in grassland or shrubland (Jonsen et al. 2001); dispersal occurs slowly over several years between release plots and non-release plots 100-1000 m apart in Montana and South Dakota (Butler et al. 2006).

Uncultivated fields, pastures, rangelands, and disturbed sites (such as railroad right-of-ways) where Leafy Spurge (Euphorbia esula) and related Euphorbia species present, particularly slightly moist to wet sites with loamy soils and well-developed herbaceous vegetation; possibly sites with clay soils but not very dry sites with sandy soils or those prone to flooding (Gassmann et al. 1996; Rees et al. 1996; Lajeunesse et al. 1997; Lym and Nelson 2000); in western North Dakota, beetle densities highest in shrub and grassland habitats, lowest in woodland and river bottom habitats (Larson and Grace 2004).

Host plants restricted to Euphorbia. Reported larval host plants in Europe and North America include several species in the subgenus Esula, especially E. cyparissias, E. esula, E. myrsinites, and E. virgata, to a lesser extent E. lathyris, E. oblongata, E. peplus, and E. seguieriana; no feeding on 8 other species of Euphorbiaceae from 7 genera, nor 28 species from 18 non-Euphorbiaceae families (Gassmann et al. 1996). Larvae feed in root hairs and roots (Rees et al. 1996; Lajeunesse et al. 1997; Skinner et al. 2004). In transfer tests, L1 instar larvae placed on 23 Euphorbia species and 7 genera (8 species) of other potential host Euphorbiaceae developed to L3 instar only on the Euphorbia species mentioned above (Gassmann et al. 1996). Adults raised from E. cyparissias and E. virgata show a preference for E. cyparissias, E. esula, E. incisa (native to North America), E. myrsinites, E. peplus, and E. virgata, to a lesser extent E. amygdaloides, E. lathyris, E. marginata, E. milii, and E. seguieriana, with occasional nibling by adults on 9 other Euphorbia species as well as the euphorbs Aleurites fordii and Ricinus communis (Gassmann et al. 1996). Adults feed on host plant leaves and flowers (Rees et al. 1996; Lajeunesse et al. 1997). Does not feed on native North American (non-target) Euphorbia brachycera in the field in South Dakota (Wacker and Butler 2006), but adults feed normally on native E. incisa under laboratory conditions (Gassmann et al. 1996).

Adult female produces about 200-300 eggs, deposited underground in small batches near host plant root and stem over several months during summer (Rees et al. 1996). Eggs hatch in about 8 days after oviposition (Lym 2005), probably spend up to 25 days as L2 instar, 35 days active feeding as L3 instar, as with the closely-related Aphthona czwalinai (Gassmann et al. 1996). Upon hatch, L1 instars migrate to root hairs and feed in roots until winter dormancy as L3 instar, in early spring L3 instar resumes feeding then moves from roots to soil and forms a cell in which to pupate; adults eclose in late spring and summer (Rees et al. 1996; Lajeunesse et al. 1997; Skinner et al. 2004).

Biological control agents are most effective when integrated with other biocontrol and traditional methods, such as herbicides, grazing, fire, and reseeding (Lajeunesse et al. 1997; Lym 2005; Joshi 2008). Aphthona lacertosa does not appear to shift feeding preference to native North American (non-target) Euphorbia when given opportunity to do so (Wacker and Butler 2006).

The following general suggestions (from Lajeunesse et al. 1997) may help insure successful collection and establishment of biocontrol insects:

1) Determine beforehand the habitat requirements for biocontrol insects to be used. Avoid sites with high ant and grasshopper populations, and seek areas free from grazing, herbicide or pesticide use. Initial release sites should be protected for up to 10 years, secondary sites need less protected time.
2) Collection should be made with minimum stress to the insects. Beetles can be collected by using a sweep net through the upper portions of leafy spurge plants 8-10 times, then dumping content into a container.
3) Release insects as quickly as possible. If moved more than 80 km or held for more than a few hours, the biocontrol species should be sorted out from other species of arthropods captured during sweeping. Biocontrol insects should be kept cool during transport through use of a cooler with refrigerated (not frozen) coolant packs.
4) Release biocontrol insects during the cool parts of a day by sprinkling over a small area (10-15 square meters) on a leafy spurge infestation of moderate density. Avoid tall, dense stands that may provide too much shade and high humidity.
5) Permits are required to transport biocontrol insects across state or provincial borders; in Montana, permits can be obtained from the Montana Department of Agriculture.

Specifically to Aphthona lacertosa, adult beetles are the life stage to transfer and introduce. Adults can be obtained by sweep-netting at sites with established beetle populations. These can be stored for several days in cardboard containers with leafy spurge leaves if kept cool, and exercised and fed periodically under warmer conditions. Overwintering larvae can be dug from frozen host plant roots and soil material, and kept frozen until several weeks before adults are desired, at which time samples are removed from cold storage and allowed to warm to ambient or room temperature, thereby permiting larvae to develop and become adults. Adults should be sprinkled directly on leafy spurge plants (Rees et al. 1996; Lajeunesse et al. 1997)

Melissa Maggio-Kassner is the coordinator for the Montana Biological Weed Control Project. She can be reached at (406) 258-4223 or mmaggio@missoulaeduplace.org

Useful Links:
Montana Invasive Species website
Montana Biological Weed Control Coordination Project
Montana Department of Agriculture - Noxious Weeds
Montana Weed Control Association
Montana Weed Control Association Contacts Webpage.
Montana Fish, Wildlife, and Parks - Noxious Weeds
Montana State University Integrated Pest Management Extension
Weed Publications at Montana State University Extension - MontGuides