Frances Osborn

Pathogenic effects of bacteria isolated from larvae of Hylesia metabus Crammer (Lepidoptera: Saturniidae).

Hylesia metabus larvae are susceptible to several pathogens indigenous to the area in which they are found. Some larvae show symptoms characteristic of bacterial infection; they become flaccid and lethargic, and show a marked loss of appetite. We isolated and identified 29 bacterial strains from live, dead and experimentally infected H. metabus larvae, and evaluated their pathogenic activity. The bacteria which caused mortality in the larvae were: Pseudomonas aeruginosa (60-93.3%), Proteus vulgaris (20%), Alcaligenes faecalis, Planococcus sp. and Bacillus megaterium (10%), at doses of 3-4 x 10(7). Although P. aeruginosa is a well-known insect pathogen, this is the first report of its pathogenic activity on H. metabus. The potential risk to humans and low virulence make it unlikely that P. aeruginosa could be used in an augmentative biological control programme. However its natural incidence may be enhanced using parasites and predators of H. metabus as carriers.

EXTERNAL MORPHOLOGY OF ABDOMINAL SETAE FROM MALE AND FEMALE HYLESIA METABUS ADULTS (LEPIDOPTERA: SATURNIIDAE) AND THEIR FUNCTION

Abstract Hylesia metabus is a species of moth, distributed principally in northeastern Venezuela. Female moths use their abdominal setae to cover their egg masses. Contact with these setae can cause a severe dermatitis in humans. Setae from males do not produce these symptoms. The external morphology of the abdominal setae in male and female moths was described and the effect of the setae on ant behavior was studied. We classified the setae into four types, S1, S2, S3 and S4. In females, two of these types were found in the dorsal region; S1 and S2 show a porous structure and measure 2000 μm and 155 μm in length, respectively. In the ventral part of the abdomen we observed three setae types, S1, S3 which are 190 μm long and have small barbs along their length directed towards the apex, and S4 which have numerous barbs at the base, but further up flatten out, with barbs along both sides, before tapering off at the apex. S4 also were found in the lateral zones of the abdomen and were the predominant type of setae covering the egg masses. Only S1 setae were found in males. Egg masses not covered by setae were examined and transported by Pheidole ants, whereas covered eggs were largely avoided. The morphology of the S3 and S4 setae types suggests that these may be related to the urticating properties reported for the moth. Ant avoidance of setae covered eggs suggests that these protect the eggs from at least some predators.

Comparison of two commercial formulations of Bacillus thuringiensis var. israelensis for the control of Anopheles aquasalis (Diptera: Culicidae) at three salt concentrations

Anopheles aquasalis larvae are salt water tolerant, preferring concentrations between 10 and 20 parts per thousand (ppt). The larvicidal efficacy of two formulations of Bacillus thuringiensis var. israelensis (Vectobac-12AS and Bactivec), was investigated against An. aquasalis at salinities of 0, 10, and 20 ppt. A probit analysis was used to calculate the lethal concentrations (LC50 and LC95) for each product at each salinity. The LC50 and LC95 were higher for Bactivec than Vectobac-12AS, and for Bactivec, the LC50 and LC95 increased with salinity. Vectobac-12AS should thus be preferred to Bactivec for An. aquasalis control, especially in saline breeding habitats.

Larvae-pupae parasitoids of Hylesia metabus Cramer (Lepidoptera: Saturniidae) in northeastern Venezuela: a case of natural biological control

The moth Hylesia metabus Cramer is considered a public health pest due to the release of urticating hairs by adult females during periodic invasions of towns and villages, producing dermatits in humans. We reported natural parasitism levels for this moth during six life cycles in two localities in northeastern Venezuela. Pupae were collected in the field and maintained under laboratory conditions (27 masculineC, 65% RH, 12L:12D photoperiod) until eclosion. In Mapire, parasitism increased from 33.0% to 91.1% in the three cycles studied, with the dipterans Belvosia spp. (Tachinidae) and Sarcodexia lambens Wiedemann (Sarcophagidae) and species from Ichneumonidae, Chalcidae, Perilampidae and Eulophidae being the most common. In Pedernales, parasitism decreased from 29.5% to 16.1%, and Belvosia spp. was the most abundant parasitoids, reaching parasitization levels between 70.7% and 96.2%. A significative parasitization by Neotheronia sp. (Hymenoptera: Ichneumonidae) (27.1%) occurred only in third life cycle. All natural enemies observed were koinobionts, larval-pupa parasitoids. The variations in the populations of H. metabus and its parasitoids in the areas studied are discussed. Belvosia spp. and S. lambens may have potential for use in integrated management program of H. metabus.

OVIPOSITION PREFERENCE AND EGG ECLOSION IN DIFFERENT SALT CONCENTRATIONS IN THE COASTAL MALARIA VECTOR ANOPHELES AQUASALIS CURRY

ABSTRACT Anopheles aquasalis is the main malaria vector in Sucre State, Venezuela. The larvae of this species are saltwater tolerant. The effects of different concentrations of salt on oviposition preference and egg survival were studied under laboratory conditions. Choice experiments with salt concentrations of 0, 10, 20, 30, and 40% in bottled water were set up for individual adult females and the number of eggs laid in each salt concentration was noted. Egg survival, as inferred by the number of hatched larvae also was determined for each salt concentration. Females preferred to oviposit in freshwater and rejected water salt concentrations of 40%, but they were neither attracted nor repelled by water with 10–30% of salt. Eggs hatched more quickly in the lower salt concentrations, but egg survival was not affected by salt concentrations of up to 20%. Thus, female oviposition preference in An. aquasalis determines egg survival.