Application of toxins from the entomopathogenic bacterium, Xenorhabdus nematophila, for the control of insects on foliage.

Larvae of the beet armyworm, Spodoptera exigua, and the diamondback moth, Plutella xylostella, and nymphs of the desert locust, Schistocerca gregaria were controlled by the application of either cell suspensions from the bacterium, Xenorhabdus nematophila or filtrates containing cell-free toxins. Since there was no significant differences between the two treatments it was concluded that toxins produced by the bacterium were responsible for the lethal effects obtained. Cells of Xenorhabdus nematophila were recovered from the haemocoele of the treated insects indicating that the bacterium, which is normally carried into the host by the J3 of Steinernema carpocapsae, was able to enter the host in the absence of the nematode vector. The entry was rapid, cells of Xenorhabdus nematophila being detected in the larvae of P. xylostella within 15 min of application of cell suspensions to chinese cabbage leaves. The possibility of using direct application of cell suspensions of X. nematophila to foliage for insect control is discussed.

The susceptibility of onion thrips, Thrips tabaci to Heterorhabditis indicus.

The potential of the entomopathogenic nematode, Heterorhabditis indicus against Thrips tabaci was tested on foliage and in soil at three concentrations. Soil treatment was more effective than the foliar treatment. At 1.5 million nematodes/m2, nearly 70% mortality was achieved with soil application whereas a similar dose applied to the foliage gave only 55% mortality. Soil application gave better mortality of onion thrips (62 %) at 1 million/m2 compared to foliar application at 1.5 million/m2. Probably this is because the nematodes are more effective against the soil dwelling prepupae and pupae stages of the thrips. The possible explanations for the differences are discussed.

Development of Pasteuria penetrans in Meloidogyne javanica females as affected by constantly high vs fluctuating temperature in an in-vivo system.

Growth room and glasshouse experiment was conducted to investigate the effect of constant and fluctuating temperatures on the development of Pasteuria penetrans a hyperparasite of root-knot nematodes. Tomato plants (Lycopersicon esculentum Mill) were inoculated with Meloidogyne javanica second-stage juveniles attached with endospores of P. penetrans and were grown in growth room at 26-29 degrees C and in glasshouse at 20-32 degrees C. The tomato plants were sampled from the growth room after 600 degree-days based on 17 degrees C/d, accumulating each day above a base temperature of 10 degrees C and from the glasshouse after 36 calendar days. Temperature affected the development of P. penetrans directly. The rate of development at constant temperature in growth room was faster than that in the glasshouse at fluctuating temperatures.

The influence of crop management on banana weevil, Cosmopolites sordidus (Coleoptera: Curculionidae) populations and yield of highland cooking banana (cv. Atwalira) in Uganda.

A field study was undertaken in Uganda using highland cooking banana (cv. Atwalira) to test the hypothesis that bananas grown under stressed conditions are more susceptible to attack by Cosmopolites sordidus (Germar). Four banana treatments were employed to create different levels of host-plant vitality: (1) high stress: intercrop with finger millet; (2) moderate stress: monoculture without soil amendments; (3) low stress: monoculture with manure; (4) high vigour: monoculture with continuous mulch and manure. Adult C. sordidus were released at the base of banana mats 11 months after planting and populations were monitored for three years using mark and recapture methods. Cosmopolites sordidus density was greatest in the mulched plots which may have reflected increased longevity and/or longer tenure time in moist soils. Lowest C. sordidus numbers were found in intercropped banana. Damage, estimated as percentage corm tissue consumed by larvae, was similar among treatments. However, the total amount of tissue consumed was greater in mulched banana than in other systems. Plants supporting the heaviest levels of C. sordidus damage displayed bunch size reductions of 40-55%. Banana yield losses ranged from 14-20% per plot with similar levels in the intercropped and mulched systems. Yield reductions, reported as t ha-1, were twice as high in the mulched system as in the intercrop. The results from this study indicate that C. sordidus problems are not confined to stressed banana systems or those with low levels of management, but that the weevil can also attain pest status in well-managed and productive banana stands.

Cuticle heterogeneity as exhibited by Pasteuria spore attachment is not linked to the phylogeny of parthenogenetic root-knot nematodes (Meloidogyne spp.).

The cuticle is a major barrier prohibiting the infection of nematodes against micro-organisms. The attachment of bacterial spores of the nematode hyperparasite Pasteuria penetrans (PP1) to field populations of root-knot nematodes (RKN, Meloidogyne spp.) from Burkino Faso, Ecuador, Greece, Malawi, Senegal and Trinidad and Tobago were assayed in standard attachment tests. The attachment of spore population PP1 to different field populations of root-knot nematode showed that the rates of attachment differed between countries. Similar tests were also undertaken on P. penetrans spores from these countries against 2 species of RKN, M. incognita and M. arenaria. The results showed a high degree of variability in spore attachment with no clear distinction between the 2 species of nematode. It has been hypothesized that Pasteuria spore attachment is linked to nematode species designations and this study clearly shows that this is not the case. Further tests showed that variation in spore attachment was not linked to nematode phylogeny. The results therefore beg the question of how do parthenogenetic root-knot nematodes maintain cuticle variability in the face of such an aggressive hyperparasite.

Investigations into the biochemical basis for nematode resistance in roots of three musa cultivars in response to Radopholus similis infection.

The Musa cultivars, Dwarf Cavendish, Yangambi Km5 and Kunnan, exhibit considerable differences in resistance to Radopholus similis. Infection resulted in significant increases in condensed tannins and flavan-3,4-diols in roots (P < 0.001). The highly resistant cultivar Kunnan had the highest levels of condensed tannins before and after infection. The preinfection levels were similar to the postinfection levels of the two other cultivars. Tannins had mostly procyanidin character, but Kunnan also contained propelargonidins; these compounds may be involved in the resistance mechanism. It is suggested that the butanol/HCl assay be used as a rapid test in screening for resistance to R. similis.

Identification and characterization of excreted-secreted products and surface coat antigens of animal and plant-parasitic nematodes.

Nematode surface coat (SC) proteins and excreted-secreted products (E-S) are likely to play important roles in the host-parasite interaction and considerable similarities can be found in SC proteins and E-S products from certain plant and animal parasitic nematodes. Monoclonal antibodies raised to E-S products of plant-parasitic nematodes were shown to cross-react with E-S products and the surface coats of the animal parasites Trichinella spiralis and Haemonchus contortus. Most of the antibodies recognized carbohydrate epitopes but the activity of 2 MAbs (IACR-CCNj.2a.15 and IACR-Misec.8D.3) which recognized proteic epitopes in these nematodes were further characterized. Antibody 2a.15 recognized the SC and oral exudate of Meloidogyne incognita, T. spiralis and H. contortus. This antigen was also immunolocalized in the lining of the oesophagus and gut and in the exudate present during ecdysis of H. contortus L3. Antibody 8D.3 reacted with the SC of these nematodes on cryosections but on live nematodes the immunofluorescence was very patchy and was shed from the nematode SC.

Effects of Fluctuating Temperatures and Different Host Plants on Development of Pasteuria penetrans in Meloidogyne javanica.

Greenhouse and growth room experiments were conducted to investigate the effect of host plant in relation to different nematode inoculum levels, and temperature fluctuations on the development of Pasteuria penetrans. Host plant affected the development of P. penetrans indirectly through its effect on nematode development. Endospores collected from Meloidogyne javanica females reared on different hosts did not show any differences in subsequent attachment and infectivity. The numbers of endospores produced per infected female were reduced with increasing numbers of females parasitizing okra and tomato roots. Fluctuating temperatures retarded the development of P. penetrans. The life cycle of the parasite was completed faster at approximately constant temperatures close to 30 degrees C than when the temperature fluctuated away from 30 degrees C. The temperature of irrigation water did not affect the duration of life cycle of P. penetrans.

Efficient expression of protein coding genes from the murine U1 small nuclear RNA promoters.

Few promoters are active at high levels in all cells. Of these, the majority encode structural RNAs transcribed by RNA polymerases I or III and are not accessible for the expression of proteins. An exception are the small nuclear RNAs (snRNAs) transcribed by RNA polymerase II. Although snRNA biosynthesis is unique and thought not to be compatible with synthesis of functional mRNA, we have tested these promoters for their ability to express functional mRNAs. We have used the murine U1a and U1b snRNA gene promoters to express the Escherichia coli lacZ gene and the human alpha-globin gene from either episomal or integrated templates by transfection, or infection into a variety of mammalian cell types. Equivalent expression of beta-galactosidase was obtained from < 250 nucleotides of 5'-flanking sequence containing the complete promoter of either U1 snRNA gene or from the 750-nt cytomegalovirus promoter and enhancer regions. The mRNA was accurately initiated at the U1 start site, efficiently spliced and polyadenylylated, and localized to polyribosomes. Recombinant adenovirus containing the U1b-lacZ chimeric gene transduced and expressed beta-galactosidase efficiently in human 293 cells and airway epithelial cells in culture. Viral vectors containing U1 snRNA promoters may be an attractive alternative to vectors containing viral promoters for persistent high-level expression of therapeutic genes or proteins.

Nematicidal effects of oxamyl applied to leaves of banana seedlings.

Foliar applications of oxamyl prevented nematodes from invading roots of diploid bananas. One spray with 1,250 microg/ml was more effective than 1, 2, or 3 sprays with 625 microg/ml applied at 5-day intervals. After 3 sprays with 1,250 microg/ml, invasion may be prevented for up to 4 weeks and possibly longer. Washing roots after oxamyl treatments prevented nematicidal control. When applied to nematode-infected plants, three sprays of oxamyl decreased nematode populations in the roots.