Mango is an important fruit crop and it is attacked by about 492 species of insects, 17 species of mites and 26 species of nematodes of which 188 species are from India (Tandon and Verghese, 1985; Srivastava, 1998). The mango nut weevil Sternochetus mangiferae is a specific pest on mango and it is known from all principal mango growing areas (Dey and Pande 1987), and mainly from south India including Andhra Pradesh (Ramakrishna Ayyar 1940). The grubs and adults feed on the endocarp of the fruit and hasten its maturity resulting in early fruit drop (Subramanyam, 1925; Peter Follett, 2002). It causes losses up to 90% of marketable fruits in the export market (Bagle and Prasad, 1985; Verghese, 2000). The weevil also reduces seeds germination and seed as a source of rootstocks is a concern. The import of Indian mangoes into USA has been withheld for the reason that it might be introduced there (Sundarababu, 1966). The quarantine restrictions prevent the export of fresh mangoes into uninfected areas (Hansen, 1983). Prevention of nut weevil incidence is essential to get better price for produce. Considering the economic importance of the pest, experiments on the behavior and management of S. mangiferae were carried out under field conditions in the present study.

Six-year studies were carried out at the Horticultural Research Station Farm, Ananthrajupeta (13.9976°N, 79.3304°E). The data was collected for off season shelter by examining the adult weevils/ 100 trees, number of eggs in 200 fruits for the preferential sites of oviposition within the fruit of mango, and for adult emerging sites 100 fruits were inspected and expressed as %. For management aspect, experiment was conducted for three years period at the HRS Farm, on Neelum cultivar with seven treatments viz., spinosad 45SC @0.3ml/ l, triazophos 40EC @1ml/ l, profenophos 50EC @2ml/ l, thiodicarb 70WP@1g/ l, indoxacarb 14.5SC @1ml/ l, and emamectin benzoate 5SG @0.75g/ l with three replications and in randomized block design (RBD). The spraying of insecticides was carried at marble stage of the fruit and for data recording on nut weevil damage, fruits were collected at the time of harvest and destructive sampling followed. The sample size was 50 fruits/ replication and expressed as % damage. The data was subjected to statistical analysis using ANOVA.

The results on the preferred sites for oviposition of S. mangiferae revealed that in the first year of observation, female S. mangiferae prefer to lay eggs in sinus (lower) portion of the fruit (18 eggs) followed by middle (7) and pedicel portion (4); while the third year data s showed a different trend- maximum number of eggs were laid in middle portion of fruit (25 eggs) Ecology of mango nut weevil Sternochaetus mangiferae (F.) and efficacy of insecticides 1067 D Srinivasa Reddy followed by sinus (9 eggs) and pedicel (upper) with 7 eggs; and same trend was noticed later (IV, V and VI years) indicating that the S. mangiferae female prefers the fruit middle portion for oviposition (Table 1). In contrast, females were observed to oviposit on infested fruit (Hansen et al., 1989), and lay eggs mostly on the sinus of the fruit or sometimes on the stems (Shukla et al., 1985). The observations with regard to emerging sites of S. mangiferae indicated that maximum weevils emerged from middle portion of the fruit and negligible (0.50%) emerged from sinus (lower) portion (III year data); similarly in fourth, fifth and sixth years, 98.50, 98.00 and 98.50% emerging from middle portion, respectively; the mean data over a four-years period revealed 98.62% emergence was from middle portion followed by 1.37% from sinus and negligible of 0.25% from pedicel part. Maximum number of S. weevils prefer to hide in trunk bark, cracks and crevices (11.67) followed by leftover and collected nuts (3.83) and fallen leaves and debris (2.17). Pinese and Holmes (2005) indicated that adult weevils can live for two years, so even with a crop failure in one season some weevils can survive into the following year through hide in trunk bark. Robert et al. (2006) noted that weevils overwinter under loose bark around the base of mango trees or in the forks of branches.

The efficacy of insecticides evaluated for three years revealed mean infestation levels between 8.66 to 23.33% in treated plots and 32.00% in untreated control. The pooled data showed that spinosad was the best treatment (8.66% damage) and the next best was profenophos (11.33%). These observations corroborate those of Karuppaiah (2015) on spinosad 2.5SC, and indoxacarb 14.5EC also found to be superior in ber). Muriuki et al. (2011) noted that chlorpyriphos band applied once per month + sanitation reduced the infestation. Ramakrishna Rao (2015) observed that carbaryl was effective followed by endosulfan and malathion. Emamectin benzoate (15.33%), indoxacarb (16.33%), thiodicarb (19.330%), triazophos (23.33%) reduced the damage (Table 2). Verghese et al. (2004) in their studies observed infestation levels between 3.3 and 14.8% from plots treated with synthetic insecticides against a mean of 33.0% in the untreated control plot.

Number of eggs/200 fruits;

Number of weevils/100 trees

Figures in parentheses arc sign √ % transformed values

References