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PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Mitey promising biological control agent for Paropsis charybdis?

Scion is the leading provider of forest-related knowledge in New Zealand
Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.

From Forest Health News 235, April 2013.

A collaboration with Australian forest entomologist Dr Helen Nahrung from the University of the Sunshine Coast, Queensland, has yielded new information. Dr Nahrung and her husband Dr Owen Seeman (a mite taxonomist) have discovered podapolipid mites as sexually transmitted diseases in some Australian beetles. Dr Nahrung’s research in the last few years has revealed that many species of Australian paropsine eucalypt feeding leaf beetles are infected with their own species of external mite. The sexually transmitted mite, Chrysomelobia pagurus, which is believed to be host specific to Paropsis charybdis was previously only known from mainland Australia has now also been collected in Tasmanian populations. These sexually transmitted mites only infect leaf beetles that have over-lapping generations. Transmission of the infection occurs in P. charybdis when some of the more long lived overwintering beetles live long enough to be able to mate with the spring generation beetles that appear about December each year. In addition to C. pagurus two other potentially new species of mites were also identified from P. charybdis beetles in Tasmania, one living under the elytra and the other in the spiracles. Invasion ecology theory suggests that when a new incursion takes place, the small founder population has a greater chance of arriving in the new country free of external or internal parasites. We hypothesized a low probability that P. charybdis brought any of these mites to New Zealand with it when it first settled in Lyttelton in the 1910s, and after inspecting almost 90 beetles that Scion collected from the Central North Island in December 2012, this hypothesis has been provisionally confirmed. New Zealand beetles appear to be mite free. We have another 50 beetles collected from Southland that still have to checked for the presence of mites. Infections of podapolipid mites are probably relatively harmless while the adult beetles are active, but mortality of infected beetles has been found to increase during overwintering. Fecundity may also be reduced. There is therefore some potential that C. pagurus or the other two newly discovered mites could be investigated as potential biological control agents. They will to be added to a list of potential biological control agents that could be considered in the arsenal against P. charybdis in the future.

Those of you with a bent for the classics might be interested to know that the author of the specific name pagurus says that it is “Latin for ‘crab’ and alludes to the host Paropsis charybdis, whose specific epithet is the seamonster of The Odyssey”.1

Toni Withers

1 The Latin for crab is cancer. Pagurus is a genus of hermit crabs and it seems more likely that the etymology of pagurus alludes to the mite’s habit of sheltering under the beetle’s elytra much
in the same way that hermit crabs use empty seashells as “portable homes”. – Editor.

This information is intended for general interest only. It is not intended to be a substitute for specific specialist advice on any matter and should not be relied on for that purpose. Scion will not be liable for any direct, indirect, incidental, special, consequential or exemplary damages, loss of profits, or any other intangible losses that result from using the information provided on this site.
(Scion is the trading name of the New Zealand Forest Research Institute Limited.)

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