378 BIOLOGICAL CONTROL 



Australia, where he also discovered that it was attacked by 

 important enemies. Of the latter two Chalcid parasites (Cocco- 

 phagus gurneyi and Tetracnemus pretiosus), which were introduced 

 along with other enemies, have proved remarkably successful. 

 The Pseudococcus has become reduced to negligible numbers and 

 the saving of large annual expenditure has resulted. The 

 contention that the observed results have been due to the 

 activities of these two species of parasites is based upon the fact 

 that, without exception, the presence or absence of serious 

 infestations has been positively correlated with the absence or 

 presence of the parasites referred to (Compere and Smith, 1932). 

 The outcome has been that the Cryptolcemus has now become 

 relegated to second place and its propagation no longer has its 

 former importance. 



Among other mealybug parasites that have been introduced 

 into California the Chalcid Leptomastidea abnormis (Gir.) is 

 noteworthy. Established in 1915 from stock colonies obtained 

 in Sicily, this insect has played an appreciable part in the reduction 

 of Pseudococcus citri. Attempts have also been made to augment 

 its effectiveness by mass breeding in the county insectaries 

 referred to, and over one million examples were liberated in 1924. 

 In 1922 the Coccinellid Scymnus bincevatus was successfully 

 introduced from Cape Town, and is now an accessory in the 

 control of Pseudococcus gahani. The most important of all 

 Calif ornian citrus pests is the black scale (Saissetia olece) and the 

 biological control of this insect is one of the main projects of the 

 Citrus Experiment Station at Riverside. The ladybird Rhizobius 

 ventralis, introduced by Koebele many years ago, and the Chalcid 

 Scutellista cyanea brought in from South Africa in 1902, destroy 

 great numbers of this scale insect, but their combined activities 

 fail to exercise the standard of control demanded by the growers. 

 In 1919 the Chalcid Metaphycus lounsburyi was introduced from 

 South Africa, and it has since become well established in the 

 coastal zone of the State. In this region the life-cycle of its host 

 is such that the phases of development, upon which the Metaphycus 

 is able to breed, exist at all seasons of the year. On the other 

 hand, in the interior of the State, owing to different climatic 



