Morphology
Eggs were yellowish-white and elliptical shaped (Fig 1a). The embryo was visible through the translucent eggshell. There were five larval instars. The length and width of the egg and larval instars are given in Table 1.
The translucent empty eggshell showed a small opening on its tip after egg hatching (Fig 1b and c). First instar larva was whitish with reddish-brown on the dorsal side. The body was linear in shape with a short brown head capsule. Second instar larva similar to first instar larva but body turned into a light cream colour with dark brown head capsule (Fig 1d). Body of the third instar larva was light brownish-white with a dark brown head capsule (Fig 1d).
Fourth instar larva was similar to the third instar, but the brownish colour completely disappeared, and the larva became white- the head capsule dark brown with well-developed mandibles. Fifth instar larva was stouter than earlier instars. The full-grown larva slightly curved and ‘C’ shaped with dirty white colour. (Fig 1d) The prepupal larva stopped feeding, shrunk and became stout (Fig 1e, f and g). The prepupa turned into a milky white pupa inside the young jackfruit. The prepupa with wing pads has an eye like black spots on either side of the snout (Fig 1 h and i). The length and width of the prepupa and pupa are given in Table 1.
Adults were small blackish-brown beetles with a white mark on the prothorax and elytra. Adults were sluggish before feeding and occasionally fly in a horizontal plane. The adult female and male measured 3.78±0.91 and 3.60±0.72 mm in length and 1.5±0.05and 1.37±0.12 mm in width. The body length and width between sexes was not significantly different (t = 1.3,
P>0.05 and t = 1.4,
P>0.05).
The
Ochyromera genus belongs to the tribe Ochyromerini of the subfamily Tychiinae
(Morimoto, 1962; Clark et al., 1977) or Curculioninae according to the recent classifications
(Kuschel, 1995; Zherichen and Egorov, 1990), includes about 30 species from the Oriental and Far East part of the Palaearctic Regions. Weevils of
Ochyromera genus are abundant in the mountain area of warm to the subtropical region in South-east Asia. They have a wide range of host plants belong to Annonaceae, Caesalpiniaceae, Clusiaceae, Ebenaceae, Ericaceae, Euphorbiaceae, Illiciaceae, Lauraceae, Moraceae, Magaoliaceae, Oleaceae, Rubiaceae, Sapotaceae, Theaceae and Pinaceae
(Kalshoven, 1956; Kojima et al.1998; Oberpreiler, 1993; Kojimo and Morimoto, 1996). The weevils are known to feed on various parts of plants, i.e. seeds, fruits, flowers and leaves and pupate in the soil in leaf-mining species, i.e.
O.
miwai, or inside seed or fruit in fruit-eating weevils,
O.
suturulis,
O.
ligustri and
O.
artocarpi (Kojima and Morimoto, 1996).
Many
Ochyromera species have been recorded as pests all over the world
(Warner, 1961). However, the biology of the weevils is inadequately known. The egg of
O.
artocarpi is oval with a smooth surface and colour ranges from white to cream as reported in the sweet potato weevil
Cylas formicarius (Martin and Minoru, 1954; Cockerham, 1954).
Butani (1993) also reported that the egg of
O.
artocarpi is oval and pale yellow. The oviposition behaviour of
O.
artocarpi is similar to that of
C.
formicarius, which lays eggs singly within the cavity on a fruit
(Martin and Minoru, 1954).
Life cycle
The developmental period of egg, four larval instars, prepupa and pupa of
O.
artocarpi is presented in Table 2. The total developmental period of larval instars including prepupa and pupa was 9.04±1.51 days. The male and female
O.
artocarpi completed their life cycle in 25.18±1.09 and 26.14±1.12 days under laboratory conditions.
The gravid females of
Ochyromera artocarpi made small cavities on young jackfruits and laid eggs in them singly (Fig 2 a). The larva after hatching scraped in the outer part of the fruit. The early-stage larvae were found feeding in the pericarp region of the fruit. The full-grown larvae made damage more in-depth in the endocarp portion of the fruits (Fig 2 b and c). The freshly eclosed adult weevils fed in the pericarp region of the fruits. Adult weevils emerged from the dried fallen fruits by making small circular holes (Fig 2 f).
The larva
O.
artocarpi is of the typical curculionid form as reported in the mango nut weevil
Sternochetus mangiferae (Fabricius)
(Robert and Thomas, 2016; Pinese and Holmes, 2005). They are crescent-shaped, cylindrical, white, legless grubs. Older larval instars are compact and C-shaped.
Ochyromera artocarpi completed its life cycle with five larval stages, as reported by
Subramanian (1958). The total larval period, including prepupa of
O.
artocarpi lasted for 9.04±1.51 days, whereas
Subramanian (1958) reported that the larvae complete its development and pupate in 14-15 days. The variation in larval duration may be due to the effect of host plants and local climatic factors. Damage of
O.
artocarpi on young fruits was similar to the reports of
Subramanian (1958) and
Butani (1979). The adult weevils found to feed externally, singly or in groups, on the fruit as reported by
Butani (1993). The body measurement of adult female and male was almost similar to
O.
sonepheti (Hiroaki Kojima, 2011).
Seasonal incidence
Populations of
O.
artocarpi fluctuated during different months of a year. The initial infestation of
O.
artocarpi was observed in December coinciding with the onset of fruit set, and infestation further increased from January and reached its peak in March, and fully declined in April. The population of
O.
artocarpi was positively correlated with evaporation (
r = 0.70) and negatively correlated with precipitation (
r = -0.63) (Table 3). The small whitish grubs of
O.
artocarpi bore into tender flower buds and fruits during November to April. Affected buds and fruits fall prematurely. Adults sometimes found nibbling on leaves and feeding on the outer portion of immature fruits during March.
The population fluctuations of jackfruit bud weevil were closely associated with the weather parameters. The incidence was similar during all the three years (November - May), with a peak density in March (Fig 3). As of now, so far no information is available on the seasonal incidence of
O.
artocarpi on jackfruit and also on the genus
Ochyromera in general in India and elsewhere. Our study provided a detailed life history and incidence of
O.
artocarpi first time, and this information could be useful to develop an effective weevil management programme.
