Icerya, other mealybugs, white-footed ants, Fiji

August 2017. Images of Icerya seychellarum were sent from Fiji and there was a request for confirmation. The insects were photographed from peanuts and also from citrus. It was confirmed to be Icerya seychellarum and then there was a very protracted discussion about this mealybug and how it was on hundreds of hosts and tended by the white-footed ant, which is probably a recent introduction to Fiji. One member has documented about 250 species, with avocados, guava, palms, breadfruit, jackfruit, “losilosi”, citrus,eggplant, Heliconia, among the most seriously affected. The question is, why has it suddenly become so invasive when it has been present in Fiji since 1918? (see p. 26 Williams DJ, Watson,GW (1990) The Scale Insects of the Tropical South Pacific Region. Pt. 3: The Soft Scales (Coccidae) and Other Families.CAB International, Wallingford, U.K. 267 pp. Based on specimens examined in The Natural History Museum, London, UK, it gives the earliest dates of records of Icerya seychellarumin Fiji as: Lau Is, Lakeba, 1977; Taveuni, 1977; Vanua Levu, 1975; Viti Levu, 1918. Of course the dates reflect the times when collecting was done, rather than when the insect actually got introduced! However, there was probably a resident entomologist on Viti Levu so the 1918 date is probably closest to the date of the actual introduction.)

One suggestion involves Cyclone Winston 2 years previously. After that even the mealybug population increased rapidly and the thought was that the natural enemies had become depleted by the Cyclone and that had allowed the mealybug to increase, and in turn this allowed and increase in ants. This was likely to be the answer, more so than the development of a new strain of Icerya. New Caledonia offered to formally identify the mealybug if samples were sent in 70% alcohol.

The situation in Fiji has been written up and is appended to this entry, under the title “The 2016 Fiji ant-mealybug bioinvasion”.

As for control; the mealybug destroyer, Cryptoleamus montrousieri and Rodolia cardinalis were suggested. There was also a suggestion to rentroduce natural enemies that were previously known to be present, like Cryptolaemus montouzieri, Rodolia cardinalis, and parasitoids of Maconellicoccus hirsutus. If papaya mealybug (Paracoccus marginatus)has got into Fiji, I would recommend reintroduction of those parasitoids as well to prevent that pest causing an outbreak there if it has not got there yet.

Also mentioned was the work of Catherine Hardiman on disruption of ant/mealybug associations in grapevine, using a bifenthrin product. The references can be found below.

It appears that it is not only in Fiji that there are problems with ants and hemipterans. A note from a researcher in the US said that they were doing a slot of research on disrupting these ant/hemipteran mutualisms in citrus where the Argentine ant tends a diverse complex of honeydew producing pests. There, liquid baits (25% sucrose solution mixed with 0.0001% thiamethoxam) are used. Control is rapid – about 2-3 days and significant knockdown of very heavy ant populations is achieved and in the following weeks a surge in biocontrol of hemipteran pests is observed as expected. The same chemical is used against the little fire ant in Guam (see the entry on this database). An article on this has appeared in the Citrograph Magazine available on line: http://citrusresearch.org/citrograph/citrograph-winter-2017/#more-6574

As regards the white-footed ant, there are about 40 locations around Suva, where Technomyrmex sp. are a problem: http://piat.org.nz/problem-ants/common-invasive-ants/white-footed-ants. But that is not the only ant, Maconellicoccus hirsutus, hasalso been seen tended by ants.

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