. Restriction fragment length polymorphisms in polymerase chain reaction amplified fragments (PCR-RFLP) of mitochondrial DNA were used to differentiate species of New World screwworms (Diptera : Calliphoridae) . Twenty-seven restriction enzymes were screened on five regions of mtDNA . Eleven restriction fragment length patterns differentiated New World screwworm, Cochliomyia hominivorax (Coquerel), from secondary screwworm, Cochliomyia macellaria (F.) . Five restriction fragment length patterns were polymorphic in C. hominivorax while all fragment patterns were fixed in C . m a c e l l a r i a . Diagnostic restriction fragment length patterns were used for species diagnosis, whereas intraspecific variable patterns were used to characterize field samples and laboratory strains . The PCR-RFLP technique is flexible with regard to developmental stage of the sample and method of preservation . We were able to characterize specimens of all life stages from egg to adult including larvae preserved in alcohol and pinned adults . PCR-RFLP is rapid and inexpensive, enabling specimens to be characterized within 24 h for less than $2 .50.

No abstract

No abstract

Entornopathogenic Nematodes (Rhabditida Heterorhabditidae, Midwest ldvestock k m Res-h Labratmy, =A-AM. Deparbnent of ~t o m~l o g y , University af N e b m k Lincoln, NE 68s83 f i v h n . Entomot. 27(6): 1514-1519 (1998) A B S l ' M m The potential for entornopathogenic nematodas to cantml flies in cattle feedlots was determined by screening 40 s h i n s repmenting 8 species of H~~ Poinar and 5 species of S~~ Travassos for virulence toward 3rd-instar house flies (maggots), Musm dmmtfm L None of the 22 s h i n s of H & m d d d i h infecting maggots caused sipi6cant Ievels of mortality in a filter paper assay. Ten strains of S -inf&ed maggots, of which 7 strains (4 S. (Wdser), 2 S $ l W [Filipjev), and 1 5. w t a -k w i Nguyen & Smart) caused sign$& m o d i t y . Ten Hetemdddiitu strains and 10 Steinsrna~ strains successllly reproduced for 2 2 generations in rnagpts. N o diEemoce was obsened between 72-h survival of maggots and addt emergence. Six strains OF S t e i w m m m were selected for 10 generations on maggots and then compared with usselected lines. fio difference in pathogenicity between selected and unselmed lines was observed. Two s'trains of S. fib, SN and G'NK-36, and 2 of the best H&em&ddifi strains, H. boGgffiophom Poinm -GO and & mgfdis Poinar, Jackson & Idein HF-85 were tested h a fresh bovine manure subsbate. AU 4 h a i n s produced significaot fly mortality In the manure subhate, although the S f e l m strains had significantly lower L G values than did the HetaorfPabdihs 5pp. fie most promising strain, S . f e l f i m SH, gave LC, and U& vaitles of 4 and 82 infective juveniles per m~o t , respectively. These doses were equivalent to 2.7 nnd 55 infective juvenile per gram of manure and 5.1 and 104 infective jwedesper square centimeter of surface area Infcctive]uveniles capable of infectin$ greater wax moth larvae, Callrnia & h l b (L), survived in manure for up to 10 wk without hosts. KEY WORDS M m d m m d h , biol@cal control, feedlot, entmnopthogenic nematdes

Allozyme variation in screwworm, Cochliomyia hominivorax (Coquerel), and secondary screwworm, C . macellaria (F.), populations from northwest Costa Rica was examined . Variability was observed in 11 of 13 enzyme loci and the frequency of the most common allele was <0 .95 for 5 loci in screwworm . In secondary screwworm, 12 of 13 loci were variable and the frequency of the most common allele was <0 .95 for 6 loci . Expected heterozygosities were 0 .149 and 0 .160 for screwworm and secondary screwworm, respectively . Goodness-of-fit statistics for Hardy-Weinberg equilibrium and Wrights F statistics indicated that both species are panmictic with no evidence of population substructuring. Nei ' s genetic distances were 0.000-0 .001 for intraspecific comparisons and 0 .899-0 .916 for interspecific comparisons . The data indicate a high level of gene flow between populations within each species.

The chorion of the Cochliomyia hominivorax (Coquerel) egg is described using observations from scanning and transmission electron microscopy and light microscopy. Included are the gross structure and surface characteristics of the chorion, the basic architecture and internal components of the chorion proper, the location and function of the hatch lines, and the functional morphology of the plastron region as a respiratory structure. In the regular hexagonal arrangement and form of individual structural units, the chorion of the screwworm egg exhibits basic architectural features common to other higher Diptera. Within the open spaces of the endochorionic layer, however, are previously undescribed membranous structures of unknown function which appear to line the cavities of the endochorion. The plastron region partially encircles the micropyle (anterior end) of the egg and extends along the dorsal surface to the posterior pole; it is delineated laterally by the hatch lines. The chorion ruptures along the anterior region of the hatch lines as the larva emerges. The plastron region is composed of elaborate stalked aeropyles above a highly dissected inner reticulum. This structure is believed to function as a respiratory organ when the egg is immersed in fluid.

. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was used to characterize mitochondrial DNA (mtDNA) variation in screwworms, Cochliomyia hominivorax, and secondary screwworm, C. macellaria, from the Caribbean, North America and South America . Four amplicons, totaling 7 .1 kb, were analysed with sixteen restriction enzymes . A total of 133 restriction sites was observed in the two species, 104 in C. hominivorax, of which nineteen were variable, and ninetyfive in C. macellaria, none of which was variable . Fourteen mtDNA haplotypes were observed among eighteen C. hominivorax examined . Mean divergence between C . h o m i n i v o r a x h a p l o t y p e s ( d ) w a s 0 . 0 0 6 4 substitutions per base-pair and genotypic diversity (G) was 0 .97 . Mean divergence between C. hominivorax and C. macellaria was 0 .0824 . Cochliomyia hominivorax haplotypes could be divided into three assemblages representing North America, South America and Jamaica, based on UPGMA clustering with d values . The assemblages did not exhibit complete geographic fidelity . These data were discordant with previously published allozyme data indicating little differentiation between screwworm populations . A scenario invoking historically isolated populations coming into contact with the introduction and movement of European livestock is proposed to explain the observed population structure of screwworm.

No abstract