Sebastian A. Pelizza

Isolation of Paecilomyces lilacinus (Thom) Samson (Ascomycota: Hypocreales) from the Chagas disease vector, Triatoma infestans Klug (Hemiptera: Reduviidae) in an endemic area in Argentina

A survey for entomopathogenic fungi of the Chagas disease vector Triatoma infestans was conducted in two provinces of Argentina from March–December 2003. Field-collected insects that died in the laboratory were individually maintained in moist chamber and incubated at 22xa0°C. Triatominae adults infected with the fungus Paecilomyces lilacinus were found at El Quebracho (27°34′S–64°31′W), Santiago del Estero province, Argentina, in December 2003. Paecilomyces lilacinus was cultured and isolated from infected insects in SDAY, PYG and MEA media. Pathogenicity tests were conducted and positive results were recorded. The median survival time (MST) of T. infestans exposed to a P. lilacinus conidial suspension was 12.8xa0days, and 100% mortality occurred at 30xa0days post-treatment. This is the first record of natural infection caused by P. lilacinus in T. infestans in the world.

Entomopathogenic fungi from Argentina for the control of Schistocerca cancellata (Orthoptera: Acrididae) nymphs: fungal pathogenicity and enzyme activity

Abstract The South American locust Schistocerca cancellata (Serville) was the most serious agricultural pest in Argentina during the first half of the last century and remains as a threat when preventive control measures are relaxed in the outbreak area. In this study, we analysed in the laboratory, the effectiveness of 26 fungal strains (isolated from both insects and soil collected in Argentina) for S. cancellata control and determined the relationship between the chitinase, protease and lipase levels in these fungi and their insecticidal activities. We observed that Beauveria bassiana (isolate LPSC 1067) caused the highest mortality (90±1.03%), the highest values of chitinolytic, proteolytic and lipolytic activity were 6.13±0.05, 2.56±0.11 and 2.33±0.47, respectively, and the lowest median lethal time was 5.96 days. This is the first time that a wide variability in chitinase, protease and lipase activity as well as in virulence has been reported in a representative sample of different entomopathogenic fungal strains from Argentina.

Prevalence and distribution of parasites and pathogens of triatominae from Argentina, with emphasis on Triatoma infestans and Triatoma virus TrV.

Chagas disease is the most important endemic arthropod-zoonosis in Argentina with an estimated 1.6 million people infected with the causative agent Trypanosoma cruzi. Triatoma infestans is the main vector of Chagas disease in Argentina. A survey for parasites and pathogens of Triatominae was conducted from August 2002 to February 2005. Collections of insects were made in domiciles, peridomiciles, and in the natural habitats of the Triatominae. Insects from these collections were dissected and their organs and tissues examined for flagellates. Frass from these insects was collected and examined for detection of the entomopathogenic virus Triatoma virus (TrV) using AC-ELISA and PCR. Triatominae belonging to four species, T. infestans (n=1646), Triatoma guasayana (n=4), Triatoma platensis (n=1) and Triatoma sordida (n=5) were collected from 62 sites located in 13 provinces of Argentina. Triatoma virus and two protozoan species, Blastocrithidia triatomae and T. cruzi, the etiological agent of Chagas disease, were found infecting Triatominae. The total prevalence of TrV in 1646 T. infestans analyzed by ELISA was 9.66% (159/1646) from 7 to 13 provinces where collections were made. Triatoma virus positive triatomines were found in 17 of 62 populations when examined by AC-ELISA but in 38 of 62 populations when PCR was used for detection. The prevalence of B. triatomae in T. infestans was 0.43% (7/1646), while the prevalence of T. cruzi was 1.3% (21/1646). This is the first study on the diversity, distribution and prevalence of flagellated protozoa and TrV of Triatominae in endemic Chagas disease regions of Argentina.

Further research on the production, longevity and infectivity of the zoospores of Leptolegnia chapmanii Seymour (Oomycota: Peronosporomycetes)

The effect of temperature on the production, survival and infectivity of zoospores of an Argentinean isolate of Leptolegnia chapmanii was determined under laboratory conditions. Production of zoospores of L. chapmaniiin vitro and in vivo upon first and fourth instars larvae of the mosquito Aedes aegypti was studied at three different temperatures. Zoospores from infected larvae were infective to mosquito larvae for 51, 12, and 5 consecutive days when maintained at 25, 35, and 10 degrees C, respectively. Maximum zoospore production in infected fourth-instar larvae was 9.6+/-1.4x10(4) zoosp/larva at 48 h at 25 degrees C. The average number of zoospores produced by individual fourth-instar Ae. aegypti larvae infected with L. chapmanii was 3.57+/-0.46x10(5) zoospores during 6 consecutive days at 25 degrees C. Zoospore production in vitro was also affected by temperature with a maximum of zoospores (n=47,666/ml) produced at 25 degrees C. When zoospores produced in vitro were used as inoculum against Ae. aegypti larvae at 25 degrees C, larval mortality was recorded for 5 consecutive weeks. The encystment process for zoospores took 17-20 min; the germination of cysts (excystment) occurred 5 min after exposure in water to mosquito larvae. The minimal time of contact between zoospores and mosquito larvae to develop infection was two minutes. Infection took place by zoospore attachment onto and then penetration through the larval cuticle or by ingestion of cysts as was confirmed by histological studies. Temperature directly affected infectivity and production of zoospores in vivo and in vitro although L. chapmanii zoospores tolerate a wide range of temperatures.

Production of Oogonia and Oospores of Leptolegnia chapmanii Seymour (Straminipila: Peronosporomycetes) in Aedes aegypti (L.) Larvae at Different Temperatures

The aquatic oomycete fungus Leptolegnia chapmanii Seymour is pathogenic to mosquito larvae, but it has been little studied since it was first isolated. Although studies have been performed on different biological isolates of L. chapmanii around the world, they were made on zoospores and a very little or even nothing is known about the sexual stage (oogonia and oospores), which allows L. chapmanii to remain in the environment when conditions are not favorable. The main objective of this study was to determine the relationship between temperature and time of onset of L. chapmanii oogonia and oospores in Ae. aegypti larvae. Leptolegnia chapmanii-infected IV instar Ae. aegypti larvae were incubated at different temperatures between 5 and 45°C and photoperiod-controlled for 90xa0days. The number of oogonia and oospores was examined daily for each tested temperature. As was expected, low temperatures extended the times of oogonia formation, as much as seven times. Likewise, temperatures significantly affect the number of oogonia produced.

Use of entomopathogenic fungi combined with biorational insecticides to control Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) under semi-field conditions

Grasshoppers are among the invertebrate herbivores that cause most economic losses in grasslands throughout Argentina’s Pampas and parts of Patagonia. Chemical insecticides remain the sole option for grasshopper control in this area, despite being of significant environmental concern. Our aim was to evaluate the efficacy of combinations between three entomopathogenic fungi strains (Beauveria bassiana LPSc 1067 and LPSc1082), and Metarhizium anisopliae (LPSc 907), two biorational insecticides (luphenuron and methoxyfenozide), and a new synthetic chemical pesticide (rynaxypyr) in the control of the pest grasshopper Dichroplus maculipennis under field cage conditions. Fungal strains used were adjusted to 1 × 108, 1 × 106 and 1 × 104 conidia/ml. Insecticides were tested at three concentrations: the average concentration recommended for application in the field (100%), 50% of that level and finally 25%. Combinations of the insecticides with B. bassiana (LPSc 1067, LPSc 1082) and M. anisopliae (LPSc 907) caused higher mortality to D. maculipennis nymphs than any of the individual agents used alone. The three insecticides tested did not negatively affect the isolates of the two species of entomopathogenic fungi employed.

New records of hypocrealean fungi infecting aphids and whiteflies: pathogenicity against Myzus persicae and interaction with its predator Eriopis connexa

Abstract Occurrence of hypocrealean entomopathogenic fungi in Argentina is reported. Bioassays were performed to evaluate their pathogenicity against Myzus persicae and Eriopis connexa. The findings underscore the importance of preserving these fungi and of investigating their potential for vector control.