Biology and management of root mealybug on banana cultivars
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Date
2007
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Department of Agricultural Entomology, College of Horticulture, Vellanikkara
Abstract
A new mealybug pest, infesting the roots of banana was reported from several pockets of Palakkad district in Kerala. Investigations were carried out to study the identification of the species, extent of infestation, biology and management. Laboratory studies were carried out at College of Horticulture, Vellanikkara, Kerala Agricultural University and management studies were conducted at farmer’s field at Mannarkkad.
Preliminary survey conducted all over Kerala revealed the occurrence of pest in 108 panchayats and in ten districts of Kerala. Two species identified under genus, Geococcus were Geococcus coffeae Green, 1902 and Geococcus citrinus Kuwana, 1923. The root mealybug population was high during the month of July 2005 followed by June 2006 and August 2005.
The biology of the root mealybug, G. citrinus was attempted on potato sprouts. An adult mealybug laid an average of 79.4 eggs, translucent, pearly white in colour and elongate-oval in shape measuring 0.32 mm in length and 0.15 mm in width with an average incubation period of 8 days during March- April and 11.6 days during November- December period. On an average, 91.92 per cent eggs hatched during November-December period.
The freshly hatched nymphs were cream in colour and were found congregated beneath the waxy material and started dispersing after three to four days. The first instar nymphs (0.34 mm in length and 0.15 mm in width) took an average of 11.6 days to moult to the second instar. Three nymphal stages could be identified based on morphological dimensions and Dyars rule. The corresponding measurement for the second and third instar nymphs was 0.72 mm in length and 0.27 mm in width and 1.03 mm in length and 0.45 mm in width respectively.
Adult female mealy bug was elongate-oval in shape and creamy white in colour and measured 2.13 mm in length and 1.16 mm in width. Males were not observed in the present study.
One coccinellid predator, Scymnus (Pullus) sp. (Scymninae, Coccinellidae: Coleoptera) was observed feeding on the root mealybug in the field during the months of July 2005 and August 2005, when the mealybug population reached its peak. Rearing of the field collected predator grubs to the adult stage revealed the presence of four larval instars and a pupal stage. Eggs were not observed during the experiment. The first instar grub took one to two days to moult to the second stage. On an average, the duration of the second, third and fourth instar grubs was 2.63, 3.25 and 3.63 days respectively. The pupal period was five days and adult lived for an average of 24.63 days. The first instar grub always fed on the eggs of root mealybug, consuming 3.25 eggs per day. The per day consumption for the second, third and fourth instar grubs was 3.88, 5.75 and 9.13 nymphs respectively while adult beetle consumed 11.13 nymphs per day.
Field collected entomopathogenic fungus, Hirsutella sp. was isolated in the laboratory and the pathogenicity was confirmed by proving Koch's postulates. Spore production was high in SMA+Y media followed by PDA and RM and the lowest was in PCA. The biomass production was significantly higher in SM+Y broth followed by PD and RM and PC produced the lowest biomass. Large-scale multiplication in the half-cooked sorghum grains produced higher number of spores followed by rice grain.
3he pest was observed as early at 12 days after planting of suckers. Centella asiatica L., Ludwigia parviflora Roxb., Cyperus killinga Endl., C. iria L., C. pangorei Rottb., C. cyperinus (Retz.), Axonopus compressus Rottb., Commelina benghalensis L., Colocasia antiquorum (Schott.), Mollugo pentaphylla L., Bulbostylis barbatum Kunth. Fimbristylis miliacea, Nephrolepis spp., Vernonia cinerea and Eclipta alba seen in the mealybug infested banana field were found infested with this mealybug. The infestation was high in the field with heavy infestation especially with Cyperus spp.
Two fungi, Rhizoctonia solani and Fusarium oxysporum could be isolated from both healthy and mealybug infested roots exhibiting no association between them. Plant parasitic nematodes were present in mealybug infested banana garden but there was no significant difference with the population from healthy garden.
Out of six cultivars of banana, Palayankodan and Kodappanillakunnan were free from infestation by the root mealy bug. The pest intensity was high in Nendran and was equally severe in the cultivar, Njalipoovan.
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Among the soil ameliorants screened, sodium silicate and calcium oxide were better than calcium carbonate and salicylic acid by recording less mealybug population. Among the botanical insecticides, drenching of three per cent neem seed kernel extract (NSKE) at monthly interval stood superior at all intervals of observation in reducing the mealybug population. The entomopathogenic fungus, C. lecanii was the best among the three fungi screened. Drenching of chlorpyrifos (0.05%) at monthly intervals @ 2.5 ml l-1 was the best among the four chemicals screened.
Integrated management of the pest revealed that almost all treatment combinations containing chlorpyrifos had higher per cent reduction during different intervals of observation. Maximum per cent reduction was in the treatment chlorpyrifos alone, which recorded the maximum bunch weight and highest benefit: cost ratio.
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