S. Mahunka szerk.: Folia Entomologica Hungarica 27/2. (Budapest, 1974)
is believed to be of American origin and the Dioscorea spp. planted in Papuan New Guineán gardens most likely have their original home country somewhere in the Neotropical biogeographical region. There is little doubt that these important plants of the human economy arrived in the South West Pacific area in historical times, more than likely carried by human agencies. There are some attractive theories on the supposed route made by the sweet potato to the West and the Southwest, from the New World to the Old World but to the present date we do not have enough facts about when and how this garden crop reached the islands of South East Asia and the Soutwestern Pacific region. It is hard to imagine that the now densely populated Chimbu District of the Central Highlands of New Guinea had so many inhabitants before the sweet potato reached the highland regions of this great island. Several dozen native insects of Papua New Guinea became adapted to Ipomoea batatas as a food-plant (FROGGATT 1936a,b, 1939; SZENT-IVANY 1956(1958)a,b, 1959; SZENTIVANY et CATLEY 1960a,b; SZENT-IVANY 1961 a, b, GRESSITT 1963, SMEE 1965; ANONYMOUS 1965, 1966; SZENT-IVANY et STEVENS 1966; ANONYMOUS 1968), but a much smaller number of insects attacked Dioscorea spp. in this country (SZENT IV ANY* 1956(1958)a; D. J. WILLIAMS 1960; SZENT-IVANY 1961a, b). None of theneotropical pests of cultivated yam were accidentally introduced to Papua New Guinea. The three major pests of sweet potato however are most likely not native to this country. The sweet potato weevil, Cylas formicarius (F . ) is believed to have reached Papua New Guinea with its main food plant, Ipomoea batatas and it has reached Australia probably the same way. The original habitats of this pest which at times causes very serious damage to the sweet potato crop in Papua New Guinea, could have been in the Asian mainland where it was associated with some native Ipomoea spp.before I. batates arrived there from the East. The two other major sweet potato pests in Papua, the sphingids Herse convolvuli (L.) amd Hippotion celerio (L.) have probably come to Papua New Guinea as immigrants. Both are known from zoogeographical regions and their migration has been discussed by C. B. WILLIAMS (1971) and other authors. Before the Second World War in the 1930-s the larvae of Hippotion celerio caused severe damage to the sweet potato crop on the Gazelle Peninsula of New Britain (FROGGATT 1939) and the giant toad ( Bufo marinus ) was introduced to New Britain for the control of this hawkmoth and of malaria mosquitoes (WILSON 1963.) The only important pest of yam in Papua New Guinea is the endemic yam mealy bug, Planococcus dioscoreae WILLIAMS (SZENT-IVANY 1961a, b). It was first found in the late 1950-s in the Maprik Subdistrict of the Sepik District of New Guinea, where it caused very serious damage to yam roots kept in village storage houses, specially builtfor the storage of yam roots . The mealy bug appeared on the surface of the yam roots in very dense populations, covering them up to the thickness of 1/2 cm. A large proportion of the roots kept in the storage houses was unedible, unsuitable for human consumption. The mealy bug outbreak occurred after the spraying of the inner walls of the storage houses with chlorinated hydrocarbon insecticides against malaria mosquitoes. The inhabilitants of the villages whose livelihood depends on the yam crop to a great extent have a special pride in growing very long and healthy roots of the variety known as "long yam" which is the subject of annual competition between the villages. It is not surprising that the villagers were irritated by the sudden appearance of the dense populations of the harmful sucking insect on their precious crop and they blamed the malaria eradication pilot project of the Department of Public Health for the outbreak of the yam pest. The author who at the time was Senior Entomologist at the Headquarters laboratory of
