RESUMO
The susceptibility of 1st to 4th instars of Bemisia tabaci (Gennadius, 1989) (Hemiptera: Aleyrodidae) to three isolates of Cordyceps sp. (Hypocreales: Cordycipitaceae) was evaluated in screenhouse experiments under variable temperatures and moisture conditions. No differences in susceptibility to the Cordyceps sp. isolates were observed among 1st, 2nd, and 3rd instar nymphs with respect to median lethal time (LT50) values. Confirmed mortalities ranged from 63.7 to 87.8% when the isolates were tested at 5 × 107 conidia mL-1. The 4th instar was the least susceptible to the fungal isolates (≤ 36.6% mortality). However, 60.0 to 99.5% of the adults that emerged from 4th instar nymphs previously treated with the fungus succumbed to the infection. Temperature was more detrimental to Cordyceps sp. virulence towards B. tabaci nymphs than relative humidity (RH). At similar RH, median LT50 for 1st instar (9.4 days) was higher than for 3rd instar (5.3 days) when the fungus was tested at 5 × 107 conidia mL-1; minimal temperatures of ≥ 12.6°C compared to ≥ 17.0°C were registered for experiments with 1st and 3rd instars, respectively. However, temperatures ≥ 35°C for 4 to 6 h daily did not affect the efficacy of the fungus against nymphs. Cordyceps sp. showed high virulence to all life stages of B. tabaci at relatively low RH, and an ability to grow extensively over the leaf surface and to produce high amounts of conidia on infected hosts. These attributes certainly boost its potential as an important pest control component of B. tabaci biotype B, especially for management of populations resistant to synthetic insecticides.
Assuntos
Cordyceps/patogenicidade , Hemípteros/microbiologia , Ninfa/microbiologia , Animais , Brasil , Umidade , Controle Biológico de Vetores , TemperaturaRESUMO
AIMS: We report the first occurrence of an epizootic of the ascomycete fungus, Isaria tenuipes (teleomorph Cordyceps takaomontana), on the ocola skipper Panoquina ocola (Lepidoptera: Hesperiidae), an insect pest affecting rice in Brazil. METHODS AND RESULTS: Field surveys in flooded rice fields in the state of Goiás in Brazil were conducted, and a fungal pathogen of a caterpillar pest (P. ocola) was serendipitously found. This fungus inflicted high infection levels (average 86·2%) mainly to the pupal stage during warm, humid growing conditions. Typically, mycosed pupal cadavers produced milky-white to pale yellow synnemata bearing an average of 1·1 ± 0·2 × 109 conidia per cadaver. Based on phylogenetic analysis using beta-tubulin gene sequences, we confirmed that all 12 isolates obtained from field-mummified pupae were identifiable as I. tenuipes. CONCLUSIONS: Our data expand our knowledge on the host and geographical ranges of this mycopathogen and underscore its epizootic potential to affect a lepidopterous insect pest on rice in Brazil. This finding may facilitate the exploitation of this fungus as a mycoinsecticide. SIGNIFICANCE AND IMPACT OF THE STUDY: Isaria tenuipes may be used as an effective and environmentally friendly bioinsecticide against agricultural caterpillar pests due to its epizootic potential, as well as explored for medicinal purposes by pharmaceutical industry.
Assuntos
Hypocreales/isolamento & purificação , Lepidópteros/microbiologia , Oryza , Animais , Brasil , Inundações , Hypocreales/classificação , Hypocreales/crescimento & desenvolvimento , Lepidópteros/classificação , Filogenia , Esporos Fúngicos/isolamento & purificaçãoRESUMO
Nymph and adult biology of Glyphepomis spinosa Campos & Grazia (Hemiptera: Pentatomidae) was studied on rice plants under laboratory and greenhouse conditions. The full life cycle of G. spinosa lasted 50.1 day. Nymph development ranged from 2.7 days for the first instar up to 11.9 days for the fifth instar. The egg stage showed the highest per capita rate of mortality (0.16). Nearly 13% of all eggs were laid on the same day. The sex ratio was 0.5. The average hatching rate was 58.0%. Pre-oviposition, oviposition, and post-oviposition periods took 12.9, 34.4, and 6.2 days, respectively.
Assuntos
Hemípteros/crescimento & desenvolvimento , Estágios do Ciclo de Vida , Oryza/parasitologia , Animais , Brasil , Feminino , Masculino , Ninfa/crescimento & desenvolvimentoRESUMO
Observations on the bioecology and damage of Teratopactus nodicollis Boheman on Phaseolus vulgaris were carried out on field samples by assessing the number of larvae and root damage in 40 ha of a dry bean field from the Federal District, Brazil (16°4'28.41"W; 47°30'21.13"S). Larvae caused the greatest damage at the stage of germination, emergence, and primary leaves, producing 50 % stand reduction. Most larvae pupated in August and September, and adult emergence occurred in middle October. Some larvae were infected with the fungus Metarhizium spp., a biological agent that would be naturally controlling this insect.