Bioecology and management of ginger rhizome maggots

Abstract

A study entitled “Bioecology and management of ginger rhizome maggots” was carried out at College of Horticulture, Vellanikkara during 2013-2014, with the objective to identify the major species of rhizome maggots on ginger; to study the bioecology of major species of rhizome maggots and to evaluate eco-friendly management measures against the rhizome maggots. Surveys were conducted in farmers’ fields at Vellanikkara and Madakathara panchayats of Thrissur district as well as Pattencheri and Perumatty panchayats of Palakkad district during August, September and October months of 2013, for identification of the major species of ginger rhizome maggots. Three species of rhizome maggots were obtained in all the four locations surveyed which were identified as Mimegralla sp. nr coeruleifrons (Macquart, 1843), Eumerus figurans (Walker, 1859) and Elassogaster sp. nr linearis (Walker, 1849). This is the first report of the incidence of E. figurans in India, Elassogaster sp. nr linearis, is recorded for the first time as a ginger rhizome maggot. Mimegralla sp. nr coeruleifrons was the most abundant species in all the locations surveyed and constituted 96.26 per cent of the total number of maggots collected. E. figurans accounted for 2.96 per cent of the overall population, followed by Elassogaster sp. linearis, forming 0.82 per cent of the maggots collected. Studies on the biology of Mimegralla sp. nr coeruleifrons showed the average incubation period was about 3.75 days, while the mean duration of first, second and third instars was 2.25, 3.15 and 6.70 days respectively. The mean pupal period lasted for 8.80 days. The longevity of adult male and female fly were 43.90 and 51.00 days respectively, with a sex ratio of 1:1. The morphometric observations of the different life stages of Mimegralla sp. nr coeruleifrons showed that eggs, on an average, measured 0.75 mm in length and 0.20 mm in width. The size of the first, second, and the third instar maggots averaged 0.63 × 0.16 mm, 4.2 × 0.90 mm and 8.1 × 1.68 mm in length and width respectively, while the pupae recorded a mean length of 5.36 mm and mean width of 1.65 mm. The adult male and female flies measured 11.2 × 1.30 mm and 13.56 × 2.18 mm respectively. The average fecundity of an adult female fly was 55.4 eggs during an oviposition period of 1 to 3 days. Attempts at documentation of natural enemies revealed that Trichopria malabarensis Rajmohana and Narendran sp. nov. (Hymenoptera:Diapriidae), a gregarious pupal parasitoid, was the most important natural enemy of Mimegralla sp. nr coeruleifrons in the field. An unidentified spider belonging to the family Araneidae was observed to feed on the adult flies in the field. No pathogens were isolated from maggots collected from the surveyed locations. Two entomopathogenic fungi viz. Metarhizium anisopliae (Metschnikoff) Sorokin and Beauveria bassiana (Balsamo) Vuillemin, along with two entomopathogenic nematodes Steinernema carpocapsae Weiser and Heterorhabditis indica Poinar and two insecticides, namely, fipronil and chlorpyriphos were evaluated in the laboratory for their efficacy in managing rhizome maggots. Petri plate bioassay as well as rhizome dip bioassay revealed that chlorpyriphos (20EC) @ 300 g a.i. ha-1 to be the most effective treatment, recording cent per cent mortality within 24 h after treatment. Fipronil 5SC @ 50 g a.i. ha-1 recorded an average mortality values of 90 and 66.66 per cent in Petri plate and rhizome dip assays respectively. Among the entomopathogenic organisms, the nematode H. indica recorded 16.66 per cent mortality while the fungus M. anisopliae recorded 3.33 per cent mortality in the Petri plate bioassay. Both B. bassiana and S. carpocapsae failed to induce mortality in the treated maggots. The entomopathogens failed to record any mortality in the rhizome dip study. The pot culture studies confirmed the above findings with chlorpyriphos and fipronil recording cent per cent and 78 per cent mortality respectively. Analysis of the ginger rhizomes, twenty days after exposure to fipronil, recorded a value of 0.052 mg kg-1, marginally above the detectable limit of 0.05 mg kg-1 of rhizome. Studies on the interaction between the maggots of Mimegralla sp. nr coeruleifrons with Pythium aphanidermatum, which causes rhizome rot in ginger indicated that infection by the fungus could be independent of maggot. While all the plants inoculated with P. aphanidermatum alone, as well as the plants inoculated with P. aphanidermatum along with the maggots of Mimegralla sp. nr coeruleifrons showed rhizome rot symptoms, infestation by maggots alone, failed to produce any such symptoms. The establishment of maggots, at 70 per cent was also greater in rhizomes inoculated with the fungus, as against 42 per cent in rhizomes treated with maggots alone.