Development and Fecundity of Reesimermis nielseni,a Nematode Parasite of Mosquitoes

Maturation of the mermithid nematode Reesimermis nielseni to the adult stage began by the tenth day after emergence of the nematodes from their hosts at ambient temperatures (24-27 C). Most postparasitic males and females reached the adult stage after 50 and 70 days, respectively. The first females exhibiting egg development and oviposition were observed 25-30 days after emergence, but some oviposition was still taking place 150 days later. Reesimermis nielseni laid an average 2,480 eggs per female over an 18-day oviposition period. A majority of the mature eggs hatched within 7 h after the cultures were flooded. The preparasites are short-lived, and only a few were able to infect exposed hosts after 72 h.     

Susceptibility of Various Species of Lepidopterous Pupae to the Entomogenous Nematode Neoaplectana carpocapsae

The susceptibility of certain species of lepidopterous pupae occurring in different ecological situations to the entomogenous nematode, Neoaplectana carpocapsae, was tested. Soil- or litter-pupating lepidopterous insects were not highly susceptible to N. carpocapsae. The most susceptible insect pupating in the soil was Spodoptera exigua with 63% pupal mortality, while Harrisinia brillians, which pupates in litter, had 55% mortality. Other soil- and litter-pupating insects had mortalities of less than 25%. Some insect species that pupate above ground were highly susceptible (> 84% mortality) to N. carpocapsae infection.     

Effects of Selected Insecticides and Nematicides on the In Vitro Development of the Entomogenous Nematode Neoaplectana carpocapsae

The effects of organophosphates (mevinphos, phenamiphos, trichlorfon), carbamates (carbofuran, methomyl, oxamyl), a formamidine (chlordimeform), a synthetic pyrethroid (fenvalerate), a chlorinated hydrocarbon (methoxychlor). and an insect growth regulator (diflubenzuron) on in vitro development and reproduction of Neoaplectana carflocapsae were tested by incorporating each chemical into a nematode rearing medium. Organophosphates and carbamates adversely affected development and reproduction at concentrations ≥ 0.1 mg/ml. Phenamiphos was the most toxic, with no nematode reproduction at 0.01 mg/ml. Inoculated infective juveniles developed to adults with some of the organophosphates and carbamates, but limited or no reproduction occurred. Chlordimeform inhibited development at 1.0 mg/ml, while diflubenzuron, fenvalerate, and methoxychlor did not significantly (P > 0.05) reduced reproduction at 1.0 mg/ml. The organophosphate and carbamate nematicides in use for control of plant-parasitic nematodes may be toxic to N. carpocapsae in the soil.     

Rickettsia Species in African Anopheles Mosquitoes

Background

There is higher rate of R. felis infection among febrile patients than in healthy people in Sub-Saharan Africa, predominantly in the rainy season. Mosquitoes possess a high vectorial capacity and, because of their abundance and aggressiveness, likely play a role in rickettsial epidemiology.

Methodology/Principal Findings

Quantitative and traditional PCR assays specific for Rickettsia genes detected rickettsial DNA in 13 of 848 (1.5%) Anopheles mosquitoes collected from Côte d’Ivoire, Gabon, and Senegal. R. felis was detected in one An. gambiae molecular form S mosquito collected from Kahin, Côte d’Ivoire (1/77, 1.3%). Additionally, a new Rickettsia genotype was detected in five An. gambiae molecular form S mosquitoes collected from Côte d’Ivoire (5/77, 6.5%) and one mosquito from Libreville, Gabon (1/88, 1.1%), as well as six An. melas (6/67, 9%) mosquitoes collected from Port Gentil, Gabon. A sequence analysis of the gltA, ompB, ompA and sca4 genes indicated that this new Rickettsia sp. is closely related to R. felis. No rickettsial DNA was detected from An. funestus, An. arabiensis, or An. gambiae molecular form M mosquitoes. Additionally, a BLAST analysis of the gltA sequence from the new Rickettsia sp. resulted in a 99.71% sequence similarity to a species ({"type":"entrez-nucleotide","attrs":{"text":"JQ674485","term_id":"386870496","term_text":"JQ674485"}}JQ674485) previously detected in a blood sample of a Senegalese patient with a fever from the Bandafassi village, Kedougou region.

Conclusion

R. felis was detected for the first time in An. gambiae molecular form S, which represents the major African malaria vector. The discovery of R. felis, as well as a new Rickettsia species, in mosquitoes raises new issues with respect to African rickettsial epidemiology that need to be investigated, such as bacterial isolation, the degree of the vectorial capacity of mosquitoes, the animal reservoirs, and human pathogenicity.     

Characterization of Root-Knot Nematode Resistance in Medicago truncatula

Root knot (Meloidogyne spp.) and cyst (Heterodera and Globodera spp.) nematodes infect all important crop species, and the annual economic loss due to these pathogens exceeds $90 billion. We screened the worldwide accession collection with the root-knot nematodes Meloidogyne incognita, M. arenaria and M. hapla, soybean cyst nematode (SCN-Heterodera glycines), sugar beet cyst nematode (SBCN-Heterodera schachtii) and clover cyst nematode (CLCN-Heterodera trifolii), revealing resistant and susceptible accessions. In the over 100 accessions evaluated, we observed a range of responses to the root-knot nematode species, and a non-host response was observed for SCN and SBCN infection. However, variation was observed with respect to infection by CLCN. While many cultivars including Jemalong A17 were resistant to H. trifolii, cultivar Paraggio was highly susceptible. Identification of M. truncatula as a host for root-knot nematodes and H. trifolii and the differential host response to both RKN and CLCN provide the opportunity to genetically and molecularly characterize genes involved in plant-nematode interaction. Accession DZA045, obtained from an Algerian population, was resistant to all three root-knot nematode species and was used for further studies. The mechanism of resistance in DZA045 appears different from Mi-mediated root-knot nematode resistance in tomato. Temporal analysis of nematode infection showed that there is no difference in nematode penetration between the resistant and susceptible accessions, and no hypersensitive response was observed in the resistant accession even several days after infection. However, less than 5% of the nematode population completed the life cycle as females in the resistant accession. The remainder emigrated from the roots, developed as males, or died inside the roots as undeveloped larvae. Genetic analyses carried out by crossing DZA045 with a susceptible French accession, {"type":"entrez-protein","attrs":{"text":"F83005","term_id":"11352626","term_text":"pir||F83005"}}F83005, suggest that one gene controls resistance in DZA045.     

Effects of Host Size and Parasite Burden on Sex Ratio in the Mosquito Parasite Octomyomermis muspratti

The ratio of Octomyomermis muspratti to the host mosquito at the time of exposure had little effect on the ratio of male to female parasites that resulted. However, the ratio of males to females increased as the number of parasites/host increased. Hosts with a single nematode produced fewer than 1% males in comparison with hosts with 8 parasites which produced about 40% males; hosts with 10 or more nematodes generally produced more male than female nematodes. Males of O. muspratti usually emerged before females because of the earlier death of multiply-infected mosquitoes. The size of the host at the time of invasion bad no significant influence on nematode sex ratios. Since mating is apparently necessary for reproduction in O. muspratti, the low male to female ratios that occur will be important in developing successful mass production techniques.     

Root Penetration by Meloidogyne incognita Juveniles Infected with Bacillus Penetrans

Bacillus penetrans inhibited penetration by Meloidogyne incognita second-stage juveniles (J2) into tomato roots in the laboratory and greenhouse. Spores from this Florida population of B. penetrans attached to J2 of M. javanica, M. incognita, and M. arenaria. A greater proportion of J2 of M. javanica were infected than were J2 of either M. incognita or M. arenaria, and a greater number of spores attached to M. incognita than to M. arenaria.     

Ecological Study of Nematode Parasitism in Ips Beetles from California and Idaho

Nematodes found in Ips paraconfusus from ponderosa pine in California were an undescribed species of Parasitaphelenchus, Contortylenchus elongatus, C. reversus, and C. brevicomi. C. elongatus, the most commonly found contortylenchid, was present in 98.2% of the contortylenchid-parasitized beetles. Only one nematode parasite of the gut, a Parasitorhabditis sp., was isolated. Although significant differences in parasitism were observed, they were by collection sites, rather than by elevation or bole sources (slash or standing). Significant changes in parasitism between fall and spring collections were observed but not at every site. Nematode parasitism in the F₁ generation of I. paraconfusus by Parasitaphelenchus, Contortylenchus, or Parasitorhabditis increased or decreased from the parent generation depending upon the experiment.Nematode parasites from I. pini included an undescribed Parasitaphelenchus sp., two undescribed Contortylenchus spp., C. reversus and Parasitylenchus (= Neoparasitylenchus) ovarius from the hemocel, and Parasitorhabditis ipini from the gut. Parasitaphelenchus sp. was found in 99% and 45.3% of the beetles from Idaho and California, respectively. Of the 1,000 I. pini from Idaho and California, 157 were parasitized by the contortylenchid species or P. ovarius.     

Effects of Ph Gene-Associated versus Induced Resistance to Tobacco Cyst Nematode in Flue-Cured Tobacco

Effects of the systemic acquired resistance (SAR)-inducing compound acibenzolar-S-methyl (ASM) and the plant-growth promoting rhizobacterial mixture Bacillus subtilis A13 and B. amyloliquefaciens IN937a (GB99+GB122) were assessed on the reproduction of a tobacco cyst nematode (TCN- Globodera tabacum solanacearum) under greenhouse conditions. Two sets of two independent experiments were conducted, each involving soil or root sampling. Soil sample experiments included flue-cured tobacco cultivars with (Ph(p)+: NC71 and NC102) and without (Ph(p)-: K326 and K346) a gene (Ph(p)) suppressing TCN parasitism. Root sample experiments examined TCN root parasitism of NC71 and K326. Cultivars possessing the Ph(p) gene (Ph(p)+) were compared with Ph(p)- cultivars to assess the effects of resistance mediated via Ph(p) gene vs. induced resistance to TCN. GB99+GB122 consistently reduced nematode reproductive ratio on both Ph(p)+ and Ph(p)- cultivars, but similar effects of ASM across Ph(p)- cultivars were less consistent. In addition, ASM application resulted in leaf yellowing and reduced root weight. GB99+GB122 consistently reduced nematode development in roots of both Ph(p)+ and Ph(p)- cultivars, while similar effects of ASM were frequently less consistent. The results of this study indicate that GB99+GB122 consistently reduced TCN reproduction in all flue-cured tobacco cultivars tested, while the effects of ASM were only consistent in Ph(p)+ cultivars. Under most circumstances, GB99+GB122 suppressed nematode reproduction more consistently than ASM compared to the untreated control.     

Interaction of a solitary larval endoparasitoid, Microplitis mediator, with its host, Mamestra brassicae: host acceptance and host suitability

Abstract:  Microplitis mediator (Haliday) (Hym., Braconidae) is an important parasitoid of early instar larvae of the European cabbage moth, Mamestra brassicae L. (Lep., Noctuidae). In the laboratory, we examined attack responses of female M. mediator to the first three larval instars of M. brassicae . Females were presented with M. brassicae larvae either one individual at a time in a no-choice experiment, or three individuals, one from each instar, simultaneously in a choice experiment. Whether or not there was choice, naïve female parasitoids attacked a high proportion of larvae and did not discriminate among instars. In the no-choice experiment, attacked larvae were reared, and parasitoid cocoons were produced from about 76% of larvae attacked as first and second instars, but from only 19% of larvae attacked as third instars. Dissections of attacked larvae from the choice experiment showed that about 79% of attacks on first and second instars resulted in oviposition compared with only 49% for third instars. When given choice, frequency and number of attacks on first instar larvae increased with increasing parasitoid experience. Our results suggest that first and second instar larvae of M. brassicae are suitable hosts for M. mediator , but that third instar larvae are suboptimal both because oviposition attempts were frequently unsuccessful and because immature parasitoids failed to complete development. Nevertheless, naïve attacking parasitoids exhibited minimal discrimination among instars, although experienced parasitoids most frequently attacked first instar larvae. The host selection behaviour of M. mediator is discussed in the context of optimal foraging theory and implications for biological control.     

Morphological Comparison and Taxonomic Utility of Copulatory Structures of Selected Nematode Species

Spicules of 9 Meloidogyne, 2 Heterodera, 3 Globodera, and 12 other plant-parasitic, insect-parasitic, and free-living nematodes were excised and examined using scanning electron microscopy (SEM). Gubernacula of some of the species were also excised, and their structure was determined. The two spicules of all species examined were symmetrically identical in morphology. The spicule typically consisted of three parts: head, shaft, and blade with dorsal and ventral vela. The spicular nerve entered through the cytoplasmic core opening on the lateral outer surface of the spicule head and generally communicated with the exterior through one or two pores at the spicule tip. Spicules of Xiphinema sp. and Aporcelaimellus sp. were not composed of three typical parts, were less sclerotized, and lacked a cytoplasmic core opening and distal pores. Spicules of Aphelenchoides spp. had heads expanded into apex and rostrum and had very arcuate blades with thick dorsal and ventral edges (limbs). Gubernaculum shapes were stable within a species, but differed among species examined. The accessory structures of Hoplolaimus galeatus consisted of a tongue-shaped gubernaculum with two titillae at its distal end and a plate-like capitulum terminating distally in two flat, wing-like structures. A comparison of spicules of several species of Meloidogyne by SEM and light microscopy revealed no striking morphological differences.     

Control of Larval Northern Corn Rootworm. (Diabrotica barberi) with Two Steinernematid Nematode Species

The entomogenous nematodes Steinerema feltiae and S. bibionis did not penetrate the roots of corn, Zea mays, to infect larval northern corn rootworm (NCR), Diabrotica barberi, feeding within. Laboratory bioassays against first instar NCR indicated that S. feltiae, Mexican strain (LD₅₀ = 49 nematodes/insect) is more virulent than S. bibionis (LD₅₀ = 100). Numbers of NCR larvae in a grain corn crop were reduced by both nematode species applied at corn seeding time at the rate of 10,000 infective-stage juveniles per linear meter of corn row. The chemical insecticide fonofos provided significantly better control than either nematode species.     

IndigenousTrichogramma (Hym.: Trichogrammatidae) parasitizing eggs ofRhopobota naevana (Lep.: Tortricidae) on cranberries in British Columbia

Two indigenous species ofTrichogramma were reared from natural populations of the blackheaded fireworm,Rhopobota naevana (Hübner) infesting cranberries in British Columbia, Canada. One was identified asTrichogramma sp. nr.sibericum Sorokina and the other wasTrichogramma minutum Riley. Percentage of parasitized hosts increased during the season in an abandoned field, but decreased in a commercial field where pesticides were used. The potential ofTrichogramma as a biological control agent against the fireworm is discussed.     

Nematode Problems Affecting Agriculture in the Philippines

Nematodes are considered major pests on most economic crops in the Philippines, particularly on banana, pineapple, citrus, tomato, ramie, and sugarcane. Radopholus similis is the most destructive nematode on banana, while Meloidogyne spp. are more serious on various vegetable crops such as tomato, okra, and celery and on fiber crops such as ramie. Tylenchulus semipenetrans is a problem on citrus and Rotylenchulus reniformis on pineapple and some legume crops. Hirschmanniella oryzae and Aphelenchoides besseyi are becoming serious on rice, and Pratylenchus zeae is affecting corn in some areas. Lately, Globodera rostochiensis has been causing serious damage on potato in the highlands. Control measures such as crop rotation, planting resistant varieties, chemical nematicide application, and biological control have been recommended to control these nematodes.     

Phytoalexins and their Role in the Resistance of Plants to Nematodes

Phytoalexins are antibiotic compounds synthesized in an infected plant in response to infection. Nematodes are capable of eliciting phytoalexins in resistant plants. Resistant lima bean (Phaseolus lunatus) infected by Pratylenchus penetrans produces the phytoalexin coumestrol; soybean (Glycine max) infected by Meloidogyne incognita produces glyceollin; cotton (Gossypium hirsuturn) infected by M. incognita produces terpenoid aldehydes.     

Description of the Blueberry Root-knot Nematode,Meloidogyne carolinensis n. sp.

Meloidogyne carolinensis n. sp. is described from cultivated highbush blueberry (cultivars derived from hybrids of Vaccinium corymbosum L. and V. lamarckii Camp) in North Carolina. The perineal pattern of the female has a large cuticular ridge that surrounds the perivulval area, and the excretory pore is near the level of the base of the stylet. The stylet is 15.9 μm long and the knobs gradually merge with the shaft. The head shape and stylet morphology of the male are quite variable. The typical head and four variants, as well as the typical stylet and two variants, are described. The labial disc, medial lips, and lateral lips of second-stage juveniles are fused and in the same contour. The head region is not annulated. Mean juvenile length is 463.7 μm, stylet length is 11.9 μm, and tail length is 42.5 μm.     

Development of Meloidogyne incognita Inhibited by Digtaria decumbens cv. Pangola

Population densities of the root-knot nematode, Meloidogyne incognita, were lower after 90 days in soil planted to digitgrass (Digitaria decumbens cv. Pangola) than in soil left fallow or planted to tomato. Roots of tomato seedlings interplanted with Pangola digitgrass were less galled than were roots of tomato seedlings planted alone. Fewer second stage larvae invaded roots of Pangola digitgrass than tomato and those that entered the grass roots failed to develop beyond the late second stage.