330 A BOOK OF INSECTS 



often regarded as an unmitigated nuisance. But many 

 species confer incalculable benefits upon mankind. From 

 the standpoint of the agriculturist they are indispensable 

 as agents in the cross-pollination of flowers. Many years 

 ago Darwin conducted experiments which proved that 

 the red and white clovers are self-sterile, and that insects 

 — chiefly bees of different kinds — are responsible for all 

 the seeds which these plants produce. Insects are no less 

 important in orchards and gardens, for without their 

 timely assistance our fruit trees would yield little or 

 nothing. One observation recorded by a well-known 

 fruit-grower (Mr. R. Brown, of Somersham, Hunts) may 

 be quoted. " In 1907 " (he writes), " when we had a very 

 cold spring and bees could work only at brief intervals 

 and at short distances from home, there was an abundance 

 of fruit in three orchards close to my apiary of fifty 

 stocks. . . . with the exception of these three orchards 

 in the immediate vicinity of the apiary, there was scarcely 

 any fruit in all this district." 



The usefulness of predaceous and parasitic insects in 

 checking the increase of plant-feeding pests has been 

 emphasized more than once in the preceding pages. One 

 more instance may be cited. In 1880, by an unlucky 

 accident, a species of scale insect (Icerya purchasi) was 

 introduced from Australia into California, where it 

 attacked the orange and lemon trees, and spread rapidly 

 all over the State. So terrible were its ravages that in a 

 single year the orange crop was reduced from 8000 to 600 

 car loads. All attempts to stamp out the pest proved 

 unsuccessful, and the situation became so critical that the 

 orange-growing industry seemed doomed. In these cir- 

 cumstances the United States Department of Agriculture 

 despatched an expert, Mr. A. Koebele, to Australia, where a 

 brilliant red ladybird (Vedalia cardinulis) was found prey- 



