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Biocontrol introduction

Target pest: Alternanthera philoxeroides (Caryophyllales: Amaranthaceae), alligator weed

Agent introduced: Arcola malloi (Lepidoptera: Pyralidae) = Vogtia malloi, alligator weed moth


1982, 1983, 1984, 1987

Import source:

South America via Florida and Australia

Import notes:

Cameron et al. (1989) - the first shipment [as Vogtia malloi, subsequently reclassified as Arcola malloi] was received from Brisbane in January 1982, consisting of alligator weed stems containing larvae and pupae. This shipment was destroyed because many stems were rotten and the larvae infected with the fungus Aspergillus flavus. The second shipment was received from Sydney in December 1983; the emerging insects bred prolifically and after more than two generations in quarantine larvae were released in the field. However, these larvae were the progeny of only 47 imported individuals, so to increase variability, a third shipment was requested, arriving from Sydney in March 1984. Some of these were found to be infected by a microsporidian and were destroyed; the progeny of the others were released. However, no released A. malloi survived their first winter in the field, and in March 1987 further pupae were collected near Sydney. From the resulting colony, only offspring from adults in which no infection was found were released.


1984, 1987-88

Release details:

Cameron et al. (1989) - between late-February and early-April 1984 infested stems containing approximately 10,000 larvae from the second importation (see ‘Import notes’ section) were released at four sites near Woodhill (Auckland), Dargaville and Whangarei (Northland). In early spring 1984 further field releases were made from the third importation. Between August 1987 and February 1988, 12 releases, each consisting of approximately 5,000 eggs and/or neonate larvae or 1,000-2,000 second or third instar larvae, from the fourth importation, were made at ten sites in Northland and Auckland.


Cameron et al. (1989) - none of the 1984 releases survived their first winter in the field. Each of the ten 1987/88 release sites were visited the following autumn and A. malloi was recovered from seven of them. At five of these sites, at least one field generation had been completed. However, it is too early yet to determine if they have successfully established.

Harman et al. (1996) - Arcola malloi has established well.

Winks (2007c) - patchily established in Northland and Auckland but not as common as the alligator weed beetle (Agasicles hygrophila).

Impacts on target:

Harman et al. (1996) - Arcola malloi is suppressing areas of weed.

Winks (2007c) - large populations cause considerable damage to alligator weed and give control in some lakes and ponds. Larvae are unable to control the weed in running water that is regularly flooded and are not suited to low temperatures. Inhabits terrestrial populations of alligator weed but cannot exert sufficient control there.

Landcare Research (2017e) - it is estimated that the biocontrol agents (A. malloi and the beetle Agasicles hygrophila) are saving around $505,000 per year in Auckland and Northland, with a resulting benefit to cost ratio of 101:1.

Impacts on non-targets:

Paynter et al. (2004) - surveys record A. malloi only feeding on target plant, although lab tests predicted minor non-target damage on Alternanthera sessilis.


Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.

Harman HM, Syrett P, Hill RL, Jessep CT. (1996). Arthropod introductions for biological control of weeds in New Zealand, 1929 - 1995. New Zealand Entomologist, 19(1): 71-80

Landcare Research (2007a). New Zealand Arthropod Collection (NZAC) Biological Control Voucher Collection. Landcare Research website [Updated 2020] https://www.landcareresearch.co.nz/tools-and-resources/collections/new-zealand-arthropod-collection-nzac/databases-and-holdings/new-t2-landing-page/

Landcare Research (2017e). Alligator weed: a financial snapshot. Weed Biocontrol: What's New? 81: 4 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-81

Paynter QE, Fowler AH, Gourlay AH, Haines ML, Harman HM, Hona SR, Peterson PG, Smith LA, Wilson-Davey JRA, Winks CJ, Withers TM (2004). Safety in New Zealand weed biocontrol: A nationwide survey for impacts on non-target plants. New Zealand Plant Protection 57: 102-107 https://journal.nzpps.org/index.php/nzpp/issue/view/vol57

Winks C (2007c). Alligator Weed Moth. In The Biological Control of Weeds Book (Landcare Research) https://www.landcareresearch.co.nz/discover-our-research/biosecurity/weed-management/using-biocontrol/the-biological-control-of-weeds-book/