Plant Sanitation. 



54§ 



[June, 1909. 



notice is taken of them. All the interest 

 in Hawaii is centred upon the pests that 

 affect sugar-cane, and the work done by 

 the staff of the Sugar Planters ' Associa- 

 tion has been on such pests. One of the 

 most interesting was the introduction of 

 an egg parasite (a minute parasitic wasp) 

 of the cane leaf hopper (Ferkin&iella 

 saccharicida) some three years ago from 

 the cane fields of Queensland, by 

 Messrs. Koebele and Perkins. The leaf 

 hopper had been introduced some years 

 before with cane from Queensland, and 

 increased so rapidly that it did a great 

 deal of damage in puncturing the leaves 

 and stems. In less than two years after 

 the introduction of its parasite there 

 was a very marked difference in the 

 ravages of the leaf hopper, and though 

 there are still plenty of them in the 

 cane fields, the pest may be said to be 

 held in check. At the same time, altered 

 methods of cultivation and the intro- 

 duction of harder-stemmed varieties of 

 cane may have been factors in its 

 decrease. 



The introduction of at least, half a 

 dozen different insects from Mexico to 

 destroy the lantaua scrub growing on 

 sugar land was a daring experiment in 

 economic entomology, and could only 

 be attempted in a place like Hawaii, 

 where nearly everything on the islands 

 has been introduced from foreign lands. 

 It had been claimed that the lantana, 

 owing to these insects, was dying in 

 large areas, and in others was producing 

 no flowers or seeds. 1 found plenty of 

 evidence of the insects on the lantana 

 foliage, the most active of which was a 

 small leaf bug. This insect, feeding on 

 the underside of the leaves, often 

 defoliated the bushes, but its attacks 

 did not prevent them from throwing out 

 a fresh growth of foliage when the rains 

 set in. Again, this bug is very closely 

 allied to an indigenous species in Aus- 

 tralia that causes similar damage to the 

 cultivated olive ; it could never be intro- 

 duced into an orchard country. 



The insect that is killing the lantana 

 is the Indian mealy bug [Orthesia insig- 

 nis) known there as the 'Maui Blight' 

 which is a very serious pest in other 

 countries to tea and other plants. This 

 was accidentally introduced into the 

 islands many years ago, but has been 

 artificially spread by the planters and 

 cattlemen all over the islands. 



In California, I placed myself in the 

 hands of the Horticultural Commis- 

 sioners at San Francisco, and from there 

 travelled over nearly all the fruit-grow- 

 ing districts. The first thing I saw in 

 their office was a large cage full of living 

 specimens of the large ichneumon wasp 



busy at work depositing their eggs in 

 bundles of sticks containing codling 

 moth grubs that had been placed there. 

 This is the codling moth parasite brought 

 by Compere from Spain, which it was 

 claimed had been so successfully spread 

 all over Californian apple orchards that 

 spraying was unnecessary. The Horti- 

 cultural Commissioners had the year 

 before written to several of the Aus- 

 tralian States, offering to supply each of 

 them with colonies of this parasite for 

 £1,000. It was interesting to watch the 

 habits of this wasp in the office, but the 

 officers were unable to show me any 

 place where it could be seen at work 

 under natural conditions. Later on, 

 when visiting apple orchards in different 

 parts of the State, I found that although 

 great numbers had been turned out to 

 destroy codling moth, no one had ever 

 seen them at work in the orchards, aud 

 from their large size and dark colour it 

 is probable that the blackbirds may eat 

 most of them. 



I found several firms manufacturing 

 arsenate of lead in large quantities for 

 use for the control of the codling moth, 

 and that most of the commercial apple 

 orchards sprayed four aud five times in 

 the season, none of them relying upon 

 the codling moth parasite. 



It was just the same in the citrus 

 orchards. It has been stated in the 

 Horticultural reports that all the 

 common scale insects were either extinct 

 or completely controlled by the lady- 

 bird beetles or internal parasites. Not 

 only was fumigation carried on as a 

 regular thing all through the Los 

 Angeles districts by the Deputy or 

 County Commissioners in the com- 

 mercial orchards for red, purple, yellow 

 aud other saales, but the trees growing 

 in the parks and gardens were black 

 with different scales and the attendant 

 black fungi. In all the large packing 

 houses I visited I found them washing 

 or brushing their oranges for scale 

 insects, so that from a commercial point 

 of view the ordinary parasites of citrus 

 pests are of little value. 



Certainly there is no economic ento- 

 mologist that does not know that if it 

 were not for the many parasites that 

 attack and destroy the injurious plant- 

 destroying insects, there would not be a 

 green thing on the face of the earth. 

 But they in turn have their enemies, so 

 that there must be limitations to their 

 value. Each country has its particular 

 insect fauna, but when an insect bene- 

 ficial in its own country is introduced 

 into another land, the altered conditions 

 and surroundings may render it quite 

 valueless, 



