INSECT PESTS.

Marlborough Express, Volume XLII, Issue 102, 1 May 1908, Page 3

INSECT PESTS.

AN INTERESTING REPORT. . In view of the introduction of the ladybird into New Zealand for the purpose of aphis destruction, the appended extract from the second report of the Welcome Research Laboratories at. the Gordon Memorial College, Knartoum, which has been received by the local Health Department, dealing with experiments ma<le there since the introduction of ladybirds into the Soudan four years ago,', is of special interest. The report is b,y Dr Andrew Balfour, medical officer. of health, Khartoum. Ladybirds were introduced into the Soudan with the idea of checking the ravages of the aphides, but it has been found that no spceies of ladybird can. increase in numbers to compare with the aphis. The report states: — "The most conspicuous, as well as the most important in many cases, of the insect enemies are the ladybirds. But no species of ladybird can increase in numbers to compare wil;h an aphis. Few ladybirds have more than three or four generations a year in even warm climates, while aphides o are often grandparents before their first month of existence is finished. Thus it comes about that when conditions favour the increase of the aphis, and it has even only a short start of a ladybird enemy, the plant infested may be severely injured before the aphis is suppressed. A species of aphis (Nectarophara pisi) sometimes finds our sweetpea plants early in the spring, and, say, for a week has undisturbed possession. Then the infestation is discovered by a wandering ladybird, and she at once proceeds to avail herself of itj feeding voraciously herself, and laying eggs that her progeny may share the feast. The eggs hatch in about a week, and then a swarm of hungry larvae slay the helpless lice right and/left. Doing their' best, however, and aided by other ladybirds, which have been attracted to the; scene, they cannot even dispose of the increase. In a | few weeks the larvae turn to pupae, and then to adults. A second generation of larvae is shortly produced, and then the aphis is quickly overcome. Sometimes,, of course, the aphis is overcome more speedily, and sometimes less so; from the beginning almost there was no doubt as to ultimate suppression. The ladybird larvae wander about when their food supply is exhausted, but not having wings they do not get very far; some eventually find food and.live to propagate, but the vast majority die of starvation, or fall victims to their cannibalistic brothers, or to other foes. For weeks at a time there may be practically no aphis of any kind in the locality, and then the ladybirds become fewer and fewer, so that when aphides begin to appear again there are very few ladybirds about to find them. Other enemies of the aphis kind suffer similarly. , .These facts render it somewhat doubtful that the injuries to plants from aphides in general could be much lessened by importing new species of ladybirds, since the newcomers would suffer from the same disabilities as our native kinds." The above extract is from notes made by Mr Lounsbury, Government entomologist at Capetown, and Dr! Balfour adds the following comment on them:—"These interesting notes present^ the somewhat complex problem which has to be faced when tackling the question of aphis destruction m a practical manner. Moreover, it requires care and skill to rear captive ladybirds, and it is difficult to feed them. Still, this seems the only likely way of combating the aphis sor'ghi, and if successful, both the agriculturalist and the Treasury would greatly benefit."