Limiting spread of a unicolonial invasive insect and characterization of seasonal patterns of range expansion

  • Published source details Krushelnycky P.D., Loope L.L. & Joe S.M. (2004) Limiting spread of a unicolonial invasive insect and characterization of seasonal patterns of range expansion. Biological Invasions, 6, 47-57.


In Haleakala National Park on Maui (Hawaiian Islands) the invasive Argentine ant Linepithema humile (native to South America) is found up to 2,850 m altitude; the subalpine zone at this elevation is still largely intact, supporting native plant and arthropod communities with a high rate of endemism. The ant was first recorded in the park in 1967 and has expanded to form two separate super-colonies occupying over 500 ha, posing a growing threat, especially to native arthropods. Ant control efforts were initiated in the mid-1990s. Using Maxforce Granular Ant Bait (a bait formulated with the toxicant hydramethylnon) produced promising results; whilst eradication was not achieved in test plots, Maxforce reduced the number of foraging ants by over 90%. As well as it's effectiveness at controlling ants, advantages of using Maxforce include that it has low toxicity towards birds and mammals, is not taken up by plants and it degrades rapidly. Further trials, summarised here, were undertaken in 1996 to test the feasibility of using Maxforce to slow the rapid spread of the two super-colonies.

On 19 August 1996, Maxforce (a.i. 0.9% hydramethylnon) was aerially broadcast in a 120 × 260  m plot at a rate of 2.25 kg/ha (2 lbs/acre); this application rate had been used in prior experiments in the park. A bait hopper was suspended from a helicopter and flown over the plot on the morning of a warm, dry day to ensure maximum initial ant foraging and retrieval of bait.

Monitoring comprised monthly assessment of relative foraging ant numbers (at non-toxic bait stations; 9:1 corn syrup : fermented fish mix placed on a 7.6 × 6.3 cm (3 × 2.5 inch) index card) and boundary movements from August 1996 to 1997, in the treated plot and an adjacent untreated control plot in the second super-colony.

Foraging ants at monitoring stations decreased dramatically within two weeks of Maxforce application: average ant numbers were 29/station in treated and 32/station in control plots prior to application, falling to 1/station within two weeks of application in the treated plot, whilst remaining essentially the same (34/station) in the control plot.

Ant spread was completely halted within the treated plot over the one year study period. In contrast, the untreated colony boundary advanced an average of 65.2 m over the year; most spread took place in late summer and autumn, no outward dispersal occurred during spring and early summer.

These patterns are consistent with the idea that dispersal in this species stems from density dependent pressure rather than inherent founding behaviour. Further trials investigating the effectiveness of boundary treatments in slowing the Argentine ant invasion at Haleakala National Park are ongoing.

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