Large Bug Research Articles

Bugs in Bags: Intraspecific Competition Affects the Biogeography of the Alternate-Year Populations of Aradus cinnamomeus (Heteroptera)

Aradus cinnamomeus, a pest of pines, shows a two-year life cycle with two widely distributed parapatric alternate-year populations and a narrow overlap zone in southern Finland. To explain the dynamics of this unique biogeographical pattern the intraspecific competition hypothesis was tested by field experiments involving crowding, transplantation and mixing the two reproductively isolated populations. The study was carried out simultaneously in both the evenand odd-year populations areas (defined according to the reproduction year of the locally dominant population) and in the narrow overlap zone. In addition to the mortality of both age-classes, the growth rate of larvae and the adult size were studied in the tests. The results suggest that younger larvae are better exploitation competitors than older larvae or adults. They can penetrate deeper into smaller crevices in the bark than the larger bugs, and thus exploit a wider range of resources. However, exploitation (within test bags) competition plays only a minor role in the regulation of the biogeographic pattern of the pine bark bug. The presence of the natural background population in the test trees (mostly outside the test bags) increased the mortality of the transplantated bugs of the other age-class to about the same extent as on a highly unfavourable site. Interference competition between the two age-classes, reinforced by the impact of exploitation competition and parasitism, can reasonably well explain the parapatry of the alternate-year populations, although direct evidence for interference is still lacking.

Response of Improved Resistant Sorghum Hybrids to Natural and Artificial Greenbug Populations12

Agronomically improved greenbug resistant sorghum, Sorghum bicolor L. (Moench), hybrids infested with fewer greenbugs, Schizaphis graminum (Rondani), were damaged less and produced higher yields than a genetically comparable green bug susceptible hybrid under natural insect infestations at Lubbock, Tex. Yields of resistant hybrids were not significantly increased by insecticide treatment under natural green bug infestations. When large green bug populations were artificially created by excluding predators and parasites with screen cages, yields of resistant hybrids were reduced. Indications are that green bug-resistant hybrids with resistance incorporated from one parent should be sufficient to prevent yield loss by natural green bug population levels.

Techniques for routine and large-scale rearing ofRhodnius prolixusStål (Hem., Reduviidae)

An improved technique for small-scale rearing ofRhodnius prolixusStal on rabbits is described. For feeding, the bugs are presented in tubes closed with silk to the shaved stomachs of rabbits; between feeds the bugs are held in 1-lb glass jars at 28°C. Large-scale rearing by this method was precluded by the amount of handling required. Feeding on defibrinated blood resulted in a survival rate to the adult stage of less than 10%, but sheep on which up to 6 600 fourth instar could be fed weekly proved satisfactory hosts, although they had to be replaced after 1–9 weeks as they developed a resistance which prevented the bugs feeding. A large-scale rearing technique is described in which instars 2–5 are presented to sheep in wire cages covered with nylon netting while instar 1 and adults are fed on rabbits; between feeds the bugs are housed in 3½–7-lb glass jars or in net-covered cages. A production of 4 000 fed fourth instar or larger bugs per week for 18 months was achieved, sometimes reaching 7 000 per week.