May 26, 2008
The rhinoceros beetle that brought me to Samoa is a serious pest of coconuts because the adult chews its way into the crown of the coconut palm, feeding on the sweet juice, and if it doesn't actually mutilate the growing point and so kill the palm, it makes such a mess of the developing fronds that they lose a lot of their power to nourish the crop of nuts. For every frond that is destroyed, there is one bunch of nuts you won't get. After feeding, the beetle lays its eggs in dead coconut trunks, other other dead logs, or even in sawdust piles or compost., and the grubs, which resemble a much magnified grass grub, feed on the rotting material for about three months . When fully grown they burrow into the ground to a depth of about half a metre and pupate, emerging after another three weeks or so as adult beetles which start the whole business again.
Beetles are quite massive, being about five centimetres long and heavily built so they weigh perhaps three ounces. If you tread on one on the ground it just makes a dent in the earth and doesn't squash. Male beetles have a prominent horn on the head, and females a less prominent one, hence the name. It presumably helps in the burrowing process. Beetle larvae were supposed to have been introduced into Samoa under the German administration about 1907 when someone imported some young rubber trees from Malaysia. They were growing in compost which presumably included some larvae.
The technique for preventing beetle damage, apart from burning dead logs etc., was to cram a mixture of sawdust and insecticide into the crown of each palm, so the beetle had to burrow through it, and died in the process. Unfortunately as each new frond unfolded from the crown it exposed a new place of access for the beetle, so the sawdust mixture had to be reapplied about every month. We employed Tokelau boys to climb each palm and do this, but it was an expensive business, so was mainly confined to the area around the harbour to reduce the chances of beetles flying onto ships, and so infesting other islands. Ships that were in port overnight were even obliged to up anchor and stand a mile or so out to sea till morning, so their lights wouldn't attract the beetles. A mighty expensive pest !
We tried introducing a big wasp that would parasitise the grubs, but it only worked were the soil suited it, and that wasn't enough. There was also a fungus that attacked the grubs, but there was no satisfactory way of spreading it from log to log. All in all I don't think the beetle noticed whether I was in Samoa or not. However, just before we came back to New Zealand, a big, sad-looking Hungarian called Surany arrived from United Nlations Food and Agriculture Organisation, and he found a virus of some sort that would kill the grubs and was spread from log to log by the adults. He got it working so well that these days you have to look hard to see any rhinoceros beetle damage on palms, whereas in my day most of the palms showed damage, and many were quite mutilated or killed.
You can't win them all.
I had better luck with a virus disease of bananas, called bunchy top. Bananas don't normally produce seed so they are always transplanted as small plants (suckers) and some fool must have brought some in that had the virus in them. Its effect is to cause the plant to grow very stunted with small brittle leaves clumped together at the crown, which is what gives it the name. Affected plants produce no fruit.
The only cure is to remove affected plants and kill the underground corm so as to prevent any regrowth. So we had a gang going through all the plantations chopping down the virused plants and mutilating them so they would rot, and also killing the stump with a herbicide injection so it couldn't produce more diseased suckers. But the virus is spread from plant to plant by an aphid that can carry diseased sap on its mouthparts. So the aphids had to be killed before they could jump off. We did this by blowing insecticide dust onto the leaves before the plant was cut down. We did the dusting using a home made bellows duster like the one I later introduced to Bangladesh. One of my foremen also used the duster as a means of discipline, breaking one across the back of a recalcitrant worker.
By the time we left Samoa in 1960 it had got mighty difficult to find a banana plant with bunchy top.
There was also a caterpillar called the taro cutworm, which would sometimes strip all the leaves off a patch of taro, leaving only the mutilated leaf stalks. Mostly it was kept under control by a couple of minute parasitic wasps, but sometimes, when the wasps were having a bad year of it for some reason, the caterpillars could do quite spectacular damage. Oddly enough, though the Samoans had been growing taro for a thousand years, they hadn't cottoned on to the fact that this caterpillar turned into a pupa in the soil and then emerged as a moth, which would lay patches of eggs on new taro leaves. So when Charlie took me to see what could be done for some poor old fellow whose crop was devoured by the caterpillars, he apologised that the caterpillars had all strangely disappeared.
I said they would have gone to ground, and kicked away the loose soil with my boot and uncovered three or four pupae an inch or two below the surface. The old fellow was highly impressed, and Charlie gave me a build up too. So he gave Charlie a basket of breadfruit to take home with him. Of course the moths would emerge from the soil in a couple of weeks, and the whole business would start again if you didn't do something about it, but fortunately their egg masses were easy to see on the taro leaves if you knew what you were looking for, and a bit of a dusting with insecticide at that stage would prevent any damage.
