No abstract

Mitochondrial DNA was amplified and sequenced from eastern, western, and Egyptian strains of alfalfa weevil, Hypera postica (Gyllenhal). Eastern and Egyptian weevils differed at only 2 nucleotide sites in 1,031 base pairs sequenced; western weevils differed by 5% sequence divergence. Three restriction sites were identified which separated eastern and western haplotypes. No intrastrain polymorphism was detected in 150 weevils from Nebraska. Collections from Lincoln in eastern Nebraska and Scottsbluff in western Nebraska were fixed for the eastern and western haplotypes, respectively. Eastern and western haplotypes were found together in the same fields in a broad overlap region in central Nebraska.

ULV malathion (9.7 oz AI/acre) was applied by air to a 16 square-mile area during August of 1968, 1969, and 1970. Adult Diabrotica virgifera LeConte populations were reduced the following season by 39, 54, and 72%. No economic infestations occurred in the treated area the year following any application. Postspray migration of beetles was very limited, but adult migration during the peak emergence period the following season contributed to repopulation of the treated area. Migration and fecundity appear to be density-dependent factors which favor increases under low populations. Area suppression does not appear economically feasible, but adult control in individual fields may be an acceptable alternative to soil insecticides applied for larval control. A model was developed for timing treatments against adults; treatments between Aug. 1-15 should result in adequate population suppression to prevent damage the following season. Mid-August population levels of 1.0 beetle/ plant were an acceptable economic threshold for determining the need for control measures. The western corn rootworm, Diabrotica virgifera LeConte, is presently controlled by prophylactic application of soil insecticides at planting time; while preventing larval damage, those treatments may not greatly reduce emerging adult populations (Pruess et al. 1968). Few alternative control methods have been investigated (Hill et al. 1948, Calkins et al. 1970) and suppression for longer than 1 year has not been accomplished by a single treatment or method. The study reported here was conducted to determine the population suppression possible by adult corn root worm control within a large area prior to oviposition.

The DNA sequence of portions of the 16s rRNA and the NADH dehydrogenase subunit 4 (ND4) genes were used to determine phylogenetic relationships in the Simulium damnosum s.l. species complex. Results suggested that at least two major clades existed in the S. damnosum species complex, and that members of the S. damnosum s.l. species complex were not closely related to North American Simulium species. The sequence variability of the ND4 gene was exploited to develop a method to distinguish the sibling species of the S. damnosum s.l. species complex, based on directed heteroduplex analysis of PCR products derived from the ND4 gene. This method was capable of classifying the six sibling species into at least five groups.

1. Temporal constancy in the structure of grasshopper assemblies (about forty-five species each) from two types of North American grasslands was assessed; one site was followed 25 years and the other 7 years. 2. Densities and relative abundances varied but composition of assemblies based on ranks suggested significant structure when three or more species were included in the analysis. 3. Results compared favorably with other insect herbivore assemblies which have been examined; variability in population change was intermediate along the spectrum of organisms which have been studied.