DIAMOND-BACK MOTH

Opotiki News, Volume II, Issue 222, 18 August 1939, Page 4

DIAMOND-BACK MOTH

POSSIBILITY OF CONTROL IMPORTING OF PARASITES only Practicable means After an investigation into the depredations caused by the diamendliacic moth in New- Zealand and the jpossibilittes. of effective control, the Ibpinion is ' held, that- the greatest pos[sibility of checking this serious pest is by the importation of natural enemies. ~ t : • This conclusion is reached by Miss Phyllis L. i{d’berts<Ss'n,r)Of JJie‘ Entomology Division, Plant Research Bureau, Department of Scientific--y .and ■lndustrial Research, whose repetition investigations carried out- are published in a bulletin just issued by .the department. “The diamond-back mothg; is., a world-wide pest of crucifers-,”*-a’ fiiuninary ME the report states, “aijdf from two to 10 generations of the moth per year have 1 •■'been' rx'qpiijjed in different countries. The oval in outline, are generally found in the field on the backs of leaves.' ''Following the larval stage, a short prepupal period intervenes before pupation,- which occurs within a silken cocoon. _ The adult moths are small and grey with a characteristic,. -diamond-pattern in black on the [brewings, particularly of the male. Field! Collections “Field collections of the diamondhack moth .were made at tlie end of 1934-35' summer season and throughout tiie 1935-3(3 and the 1936-37 summers. TJie principal areas investigated have been the' ,M.ahawatn and Hawke’s Bay. and,-.in addition, material has been recejyedl from Canterbury, Wairarapa,Yand 'Taranaki. lit all. 5407 larvae and Lb4oo' pupae were collected the first- season, 5786 larvae and 11,255 pupae the third. Three species of insect parasites have been obtained from the field. “Parasitism of from O per cent-, to 18.2 per cent, was recorded in Mnita-wat-u. from 0.07 per cent, to 51.7 per cent, in Hawke’s May, from 21.-4 per cent to 42.9 per cent, in Canterbury, from 0.79 per cent to 1.48 per cent, in Wairarapa, and 0.65 per cent, in Taranaki. In the North Island parasitism reached significant proportions only at the end of a season, too late to he of value in reducing the numbers of tlioi pest. Fungys Attacks “The fungus Entonioplithora sphaerospenna is responsible for a lieavv mor.talftj'mi larvae antll pupae at certain" periods. However, those ‘ <-c>ntlitions noeessary for the spread ol Jimgal infe<-tion are normally- only 'established in the'late autuinn,... when fungal mortality is' valueless from the point of view of control. ‘‘An examination of literature shows that tiie diamond-hack moth lias only become a serious pest in those Countries, such as New Zealand, in which the majority of its natural enemies are absent. .In this country chemical control measures are impracticable for field crops;!?so thatHt appoars at present tha'jTtlie gresft possibility of ( heeling this serious pest, is hv the introduction of its natural enemies from abroad.”