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November 2001. A whitefly destroying plants of aibika (Abelmoschus), coconut, cassava and beans on stakes among others on the very remote island of Tikopia, Solomon Islands. It could be the spiraliing whitefly, Aleurodicus dispersus (Homoptera: Aleyrodidae), in which case it could be managed with the introduction of coccinellid predators and aphelinid wasps.
Actually, A dispersus first appeared in Solomon Islands about 10 years ago and a parasitic wasp (Encarsia haitiensis) was introduced by the Ministry of Agriculture, with assistance from SPC, to control it. This parasite was released on Guadalcanal and Malaita, which were the islands infested at that time. The parasite very effectively brought the pest under control, but coccinellid predators were not introduced at that time.
To decide whether spiralling whitefly is being parasitised by hymenopteran parasitoids do the following:
Collect leaves infested with the whiteflies’ immature stages (lots of white, flocculent wax) from several different sites. Lay each leaf on a well-lighted surface out of the sun, with lower surface uppermost. Use a
fine artist’s paintbrush (or, if not available, a small tuft of animal or human hair) to very gently sweep the white wax off the surface of the colony, so that the immature stages (small, rather flattened scales) become
easy to see on the leaf underside.
If all the larger specimens are pale cream/greenish-white, and the empty skins from which insects have emerged all have irregularly-shaped emergence slits, then there are no parasitoids attacking the colony.
However, if some or all of the larger immature specimens have dark material inside them, and some empty skins from which the insect has emerged each have a more or less circular exit hole bitten out of them, then there is a hymenopteran parasitoid such as Encarsia ?haitensis or Encarsia guadeloupae attacking them.
Rats
Rats were also said to be a menace on Tikopia, with the respondent mentioning that the elders say rats are ‘seasonal’ and follow a certain indication in the stars. When that star pattern moves low in the sky the rats will soon be finished! Perhaps this means that there is some kind of seasonal pattern related to a convergence of factors. Maybe a time of low tides when organic rubbish thrown away by people lies on the shore available to rats more than at other times?
The tiny white butterfly is probably a whitefly (family ALEYRODIDAE). There are several potential damaging species. For whitefly, you need to collect the nymphal stages on the leaves (like small limpets) and put into 70% alcohol. There are a range of biocontrol agents available depending on the species.
A range of oils have been used depending on the crop and species. If it is a small area, soapy water (old washing up water) can help.
As to the rats, baits of talon (brodifacoum) may be useful – a lot will depend on the situation and proximity to people, crops, etc. Rat increase is sometimes the result of habitat destruction, for example, after the El Nino-induced drought of 1997 in Papua New Guinea. This caused widespread bush fires, resulting in the loss of habitat of the large predatory animals which normally keep rat numbers down and so rat numbers increased.
With rats, it is important to consider breeding places and food availability; these are the main factors influencing populations. This might partly explain why rat problems are seasonal, most likely corresponding to cropping seasons. Destroy possible breeding places, and put out rat poison bait just before crops start to produce their charvests. Consider using ‘bait stations’ to protect baits from children, chickens, pigs, etc.
As for references, there have been a lot of studies on rats in Solomon Islands, especially in the Temotu province. Morgan Williams did a consultancy in the mid-1980s, and there were two Peace Corps volunteers in Santa Cruz at that time. Jim Stapley’s annual reports will also have some good stuff on rats on the artificial islands and David Gollifer mentions work on rats in sweet potatoes in early Dala reports. Much has been lost with the burning of Dodo Creek, but SPC may have copies. There is a book with abstracts of publications previously held at Dodo Creek (the British High Comm might be able to help too as DFID funded the publication). CABI too should have a copy.
Mention was also made of the work that Jim Wison, the SPC Rat Specialist, did on rats in Solomon Islands (including Malaita) during the 1960-70s. His reports should be at the SPC HQ in Noumea. Bamboos were cut into sections containing warfarin to control damage in sweet potatoes at Dala, Malaita. The number of stations per unit area was not recalled, but the cereal bait had to be replenished at c.7-10 day intervals to prevent build up of moulds. The rat populations and damage appeared to be cyclical.
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