Phenology of sugarcane leaf hopper Pyrilla perpusilla (Walker) (Homoptera: Lophopidae) and its natural enemies in a crop island scenario

Abstract

Population dynamics of sugarcane leaf hopper Pyrilla perpusilla (Walker) (Homoptera: Lophopidae) and its natural enemies, namely the egg parasitoid Parachrysocharis javensis Girault (= Tetrastichus pyrillae Chrawford) (Hymenoptera: Eulophidae), nymphal parasitoid Dryinus pyrillae (Kieffer) (= Lestodryinus pyrillae Kieffer) (Hymenoptera: Dryinidae) and entomophathogenic fungus Hirsutella citriformis Speare (Ascomycota: Ophiocordycipitaceae) were studied in sugarcane germplasm maintained as a crop island. During the three-year (2010–12) study period, germplasm was planted in January/February each year, and fortnightly observations of pyrilla and natural enemy abundance were recorded. In all three years, pyrilla populations began in May, peaked during September–October and declined thereafter. The proportion of adults in relation to that of nymphs was high in the beginning, decreased progressively and increased towards the end of the crop season. Pyrilla populations differed significantly among the fortnights and years. Activity of P. javensis began early in the crop season and its parasitism rates continued to reach high levels until September–October. Parasitism rates among eggs masses were the lowest in 2010 (83.3%) and highest in 2011 (96.1%). Parasitism rates within egg masses differed significantly among the three years with the lowest (36.3%) in 2010 and highest (41.4%) in 2011. The occurrence of D. pyrillae began around June and its intensity reached a peak during October–December. The mean parasitism rate of 3.1% in 2010 declined to 2.6% in 2011 and 2.1% in 2012. Field pathogenicity of H. citriformis, which began in August and ended in December, varied among the three study years with higher infection rates in adults than in nymphs. The overall infection rates increased in successive years with a significant two-fold surge in 2012 (25.4 ± 34.1%) as compared to that in 2010 (12.5 ± 16.5%). Simple and multiple correlation analysis of pyrilla populations vs. natural enemy activity showed that egg parasitism rates alone were significantly and positively related to pyrilla abundance. Similar analysis with weather parameters indicated their indistinct influence on both pyrilla and natural enemy populations.