Microdroplet application for determination of comparative topical and residual efficacy of formulated permethrin to two populations of diamond back moth (plutella xylostella L.)

An on-demand, uniform droplet generator was used to apply 120 μm diameter drops of formulated permethrin either directly onto 3rd-instar Plutella xylostella, of two Ohio populations, or onto the abaxial surface of leaf discs (1-1000 drops cm^?2) to which those larvae were subsequently exposed. Incorporating a fluorescent tracer (Saturn Yellow GT-17N) in the spray mixture confirmed that ?direct hit”? larvae had received a topical dose from a single droplet. There was little difference in the LC₅₀/LD₅₀ for either population of P. xylostella when 24 and 48 h mortality assessments from direct hits were compared, but the LD₅₀ of Celeryville larvae was 6-8 times greater than that of Fremont larvae. Residual deposits of 120 μm drops containing approximately the LC₅₀, based on the topical assays, revealed that a droplet density providing a dose per cm² leaf surface of more than 1000 times the LD₅₀ was required to cause median mortality. The efficiency of utilisation, based on the topical LD₉₅ values, was 0.0006% and 0.072% for Fremont and Celeryville larvae, respectively.     

The Present Position in the Systematics of Meloidogyne

The genus Meloidogyne includes 32 species. The main character used for differentiation is the posterior cuticular pattern of the female. This is difficult to define and often variable but in most species it is characteristic. The body length and length and shape of the tails of the larvae, and the head characters of males, can also be used in identification of some species. The morphological and physiological variability in the commonest species is so great as to suggest that they may be species complexes or that evolution may be proceeding at an observable rate. This results in some uncertainty in the systematics.     

Aging in Pacific Northwest forests: a selection of recent research

This paper provides an overview of the work reported at a symposium on age-related changes in the structure and function of forests in the United States Pacific Northwest. Some of the work presented at this meeting is reported in the peer-reviewed papers comprising this journal issue. Age-related changes in leaf structure, CO2 assimilation rate, stable carbon isotope ratio, nitrogen concentration and stomatal limitation were demonstrated at many organizational scales. At larger scales, age-related changes were reported in canopy structure and light profile, stand productivity, tree mortality and respiration. These data raise new questions about the potential interaction among the structural and functional changes in aging forests, and indicate many avenues for future research concerning tree growth and ecosystem functioning.     

Klebsiella to Salmonella gene transfer within rumen protozoa: implications for antibiotic resistance and rumen defaunation

The rumen has long been thought to be a site of gene transfer for microorganisms. Rumen protozoa (RPz) are active predators of bacteria that can harbor antibiotic resistance genes. In this study, RPz were assessed as sites of gene transfer between two bacterial species, Salmonella and Klebsiella. One Klebsiella isolate carried a plasmid bearing bla(CMY-2), encoding an extended-spectrum beta-lactamase conferring ceftriaxone resistance, while the Salmonella was susceptible to ceftriaxone yet capable of thriving within protozoa. In vitro studies revealed that ceftriaxone-resistant Salmonella could be isolated following co-incubation of Salmonella and Klebsiella with RPz obtained from adult cattle and goats. Ceftriaxone-resistant Salmonella were not recovered in the presence of an inhibitor of protozoa engulfment or when a protozoa-sensitive Salmonella was part of the co-incubation. This transfer event was additionally observed in vitro for protozoa-independent stressors although at a significantly lower frequency. The gene transfer event was related to bacterial conjugation since a conjugation inhibitor, nalidixic acid, perturbed the phenomenon. Ceftriaxone-resistant Salmonella were recovered from calves, sheep, and goats co-challenged with ceftriaxone-resistant Klebsiella and ceftriaxone-sensitive Salmonella. However, the transfer event was not observed in calves and sheep that were defaunated prior to the co-challenge. Moreover, Salmonella transconjugants were isolated from separate bovine in vivo studies involving a Klebsiella donor carrying a plasmid conferring colicin activity while no such transconjugants were obtained from defaunated calves. These results provide an important basis for evaluating and preventing the spread of antibiotic resistance and other selective advantages for pathogens present in ruminants.     

Neurohistologic and ultrastructural lesions in cattle experimentally intoxicated with the plant Prosopis juliflora

Intoxication by pods of Prosopis juliflora (mesquite beans) causes an impairment of cranial nerve function in cattle and goats. In goats, vacuolation of neurons in the trigeminal motor nuclei has been reported. To study the lesions in cattle caused by consumption of P. juliflora pods and dry ground pods, eight 6- to 12-month-old male cattle were divided into 4 groups: group 1 was fed a ration containing 50% of pods; groups 2 and 3 received a ration containing 50 and 75% of dry ground pods, respectively; group 4 was the control. After 200 days, all cattle were killed and sampled for histologic evaluation. Samples of the trigeminal motor nucleus were examined by electron microscopy. All cattle from groups 1, 2, and 3 showed clinical signs resulting from impaired function of cranial nerves V, IX, X, and XII, starting 45-75 days after consumption of the plant. The main histologic lesions were vacuolation and loss of neurons in trigeminal motor nuclei and other motor cranial nerve nuclei with Wallerian-like degeneration in the cranial nerves. Mild denervation atrophy was observed in the masseter and other masticatory muscles. On electron microscopy, neurons of the trigeminal nuclei had markedly swollen mitochondria, with the mitochondrial cristae displaced peripherally, disoriented and disintegrating. Intoxication by P. juliflora seems to have a novel pathogenesis, characterized by a selective, primary, chronic, and progressive injury to mitochondria of neurons of the trigeminal and other cranial nerve nuclei. Cranial nerve degeneration and denervation atrophy of the muscles occurs as a consequence of the neuronal lesion.     

SSR markers for marker assisted selection of root-knot nematode (<Emphasis Type="Italic">Meloidogyne incognita</Emphasis>) resistant plants in cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L)

Cotton (Gossypium hirsutum L) cultivars highly resistant to the southern root-knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] are not available. Resistant germplasm lines are available; however, the difficulty of selecting true breeding lines has hindered applied breeding and no highly resistant cultivars are available to growers. Recently, molecular markers on chromosomes 11 and 14 have been associated with RKN resistance, thus opening the way for marker assisted selection (MAS) in applied breeding. Our study aimed to determine the utility of these markers for MAS. Cross one was RKN resistant germplasm M240 RNR × the susceptible cultivar, FM966 and is representative of the initial cross a breeder would make to develop a RKN resistant cultivar. Cross two consists of Clevewilt 6 × Mexico Wild (PI563649), which are the two lines originally used to develop the first highly RKN resistant germplasm. Mexico Wild is photoperiodic. We phenotyped the F₂ of cross one for gall index and number of RKN eggs per plant and genotyped each plant for CIR 316 (chromosome 11) and BNL 3661 (chromosome 14). From this, we verified that MAS was effective, and the QTL on chromosome 14 was primarily associated with a dominant RKN resistance gene affecting reproduction. In the first F₂ population of cross two, we used MAS to identify 11 plants homozygous for the markers on chromosomes 11 and 14, and which also flowered in long days. Progeny of these 11 plants were phenotyped for RKN gall index and egg number and confirmed as RKN highly resistant plants. Generally about 7–10 generations of RKN phenotyping and progeny testing were required to develop the original RKN highly resistant germplasms. Our results show that commercial breeders should be able to use the markers in MAS to rapidly develop RKN resistant cultivars.