Distribution, host range, and climatic constraints on Centistes gasseni (Hymenoptera: Braconidae), a South American parasitoid of cucumber beetles, Diabrotica spp. (Coleoptera: Chrysomelidae).

The genus Diabrotica includes a large number of pest species, including some of the most important crop pests of the Americas. The parasitoid Centistes gasseni Shaw is the first braconid to be described parasitizing Diabrotica in South America, and high natural infestations are reported. Field and experimental observations on the host range, distribution and biology of this parasitoid are described. Centistes gasseniwas collected in southern Brazil, eastern Paraguay and northeastern Argentina, in a region comprising humid lowlands and highlands, and cool temperate to warm subtropical climates, with regular rainfall in excess of 1300 mm. Three Diabroticaspecies, D. limitata (Sahlberg), D. speciosa (Germar) and D. viridula (Fabricius) were found to host the parasitoid, with mean percent parasitism of 5.4, 2.0 and 1.0%, respectively. Diabrotica speciosa and D. viridula are the two most important pest Diabroticaspecies in South America. Laboratory experiments with field-collected beetles and parasitoid cocoons indicated that C. gasseni overwinters in adult host beetles, remaining dormant in its live host below developmental temperatures. A potential distribution of C. gasseni in North America is proposed based on its known climatic range and the distribution of the main pest species of adult overwintering North American Diabrotica.

Effect of a phloxine B-cucurbitacin bait on diabroticite beetles (Coleoptera: Chrysomelidae).

Cucurbitacin E glycoside, extracted from a bitter mutant of Hawkesbury watermelon [Citrulls lanatus (Thunb.) Matsum. & Nakai (Syn. Citrullus vulgaris Schrad)] is the active ingredient of a feeding stimulant for the corn rootworm complex. It is the primary component of a water-soluble bait that can be combined with toxins for adult diabroticite control. Studies were conducted using phloxine B (D&C Red 28), a xanthene dye, as the toxin. This dye was efficacious against Diabrotica undecimpunctata howardi Barber, spotted cucumber beetle, and Acalymma vittatum (F.), striped cucumber beetle, in cucumber plots and could be recovered from cucumber leaves for 8 d after treatment. The average amount of dye recovered per dead spotted cucumber beetle at 8 d after treatment was 0.173 microg. Concentrated and sugar-free fermented forms of the watermelon extract were developed and compared with the fresh juice in field applications on cucumber plants. There was no significant difference in mortality of beetles from phloxine B-bait prepared with fresh, fermented, or concentrated extract, although in laboratory studies, fermented juice had higher feeding stimulant activity.

Rapid high-performance liquid chromatography method to quantitate elaterinide in juice and reconstituted residues from a bitter mutant of hawkesbury watermelon.

A C(18) reversed-phase HPLC method has been developed to analyze the concentration of 2-O-beta-D-glycopyranosyl-cucurbitacin E (synonym, elaterinide) in juice or reconstituted residues of juice derived from a bitter mutant of Hawkesbury watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai. The method requires only two steps (homogenation and filtration) for sample preparation prior to column injection and, thus, is amenable to processing large numbers of test samples. Percent elaterinide in juice samples from whole fruit, processed in various ways, ranged from 0.0230 to 0.0808%. Error differences in percent elaterinide for repetitive analyses within the same lot of juice ranged from 1.2 to 5.6%.

Intraspecific mitochondrial DNA variation in the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae).

Restriction endonuclease analyses of mitochondrial DNA (mtDNA) were used to examine genetic variability and population structure in Leptinotarsa decemlineata (Say). A group of three enzymes, EcoRI, HpaI, and PstI, was used to reveal polymorphism both within and among some of the 10 populations tested, yielding 16 haplotypes in combination. The frequencies of these 16 haplotypes differed significantly across geographic regions, indicating some partitioning of mtDNA haplotypes. Estimates of mtDNA sequence divergence (delta) between haplotypes ranged from 0.016 to 0.135%, suggesting local differentiation of mtDNA in some populations. Analysis of these data suggests that Texas was colonized by more than one mtDNA lineage, most likely originating in Mexico. We hypothesize that a larger founder size for the initial introductions or high levels of variability in the parent population at the edge of the CPB expanding range led to the initial partitioning of haplotypes observed in samples from Texas.