Lissorhoptrus oryzophilus

Taxobox
name = Rice weevil
status =


image_width =
image_caption =
regnum = Animalia
phylum = Arthropoda
classis = Insecta
ordo = Coleoptera
superfamilia =
familia = Curculionidae
genus = "Lissorhoptrus"
species = "L. oryzophilus"
binomial = "Lissorhoptrus oryzophilus"
binomial_authority = Kuschel, 1952The Lissorhoptrus oryzophilus is a insect, coleopter, native of the American continent, diffused in the oriental south states of USA, in Mexico, Canada, Cuba, Dominican Republic, Colombia, Suriname and Venezuela; recently it has appeared in the most greater rice-growing areas of Asia (China, India, Japan, Korea and Taiwan); in Europe it is most diffused in Italy, in the regions of the Piedmont and Lombardy.

The insect

The larva, completely aquatic, is whitish, to form of a "C" and to maturity it reaches the 8 mms of length. The larva introduces a pair of connected dorsal hooks to the tracheal system that are inserted in the aerial parenchyma of the guests plants roots.

It completes 4 stadiums in about 21 days. The impupament happens in a little isolated coccon, covered with mud, attached to the roots and the stadium of pupa endure around 7 days.The eggs are cylindrical, long 0.8 mms and wide 0.14 mms of pearly white color; introduces a very thin corion, very sensitive to the manipulations and they result difficult to retrieve for the small dimensions and because they are inserted in the leaf scabbards or, some times, in the roots.

The adult, of oval-lengthened form, measure 3.3-3.7 mms, inclusive the rostrum. The teguments are brown reddish, covered by smooth and shiny wide scale, that is brown clear to the sides and brown ax in the median part of the body and elytrons, where they form a varying spot for extension.

The legs are moderately strong: particularly those medians introduce along the external border of the tibias long hair, index of the adaptation of the insect to the aquatic environment.

Biology

The adult nourishes him some colth of the young leaves of the rice and of other infestant monocotyledonus, emergent from the water, provoking, with his apparatus oral chewer, longitudinal scarification of various length, parallel to the leaf nervous systems. Such alteration is the sign of the presence in field of the insect, but it is not the cause of the economic damage.

The true damages are due to the larvas that, escaped by the eggs deposed in the scabbard of the part submerged of the leaf, they nourish them some roots provoking real breaking of the same.

The stricken plants introduces development meeting place, scarce sucker growth and lesser weight of the grains. Sometimes they are easily eradicated by the turbulence of the water. In case of strong infestations the loss of production can reach 30%.

The adult winterss in diapause (without developing some activity) to the feet of the infestants on the banks or in the litter of the wooded stains near the rice fields and just in spring, when the temperatures overcome the 21°C, they moving in flight, or walking, toward the rice fields, where they begin to feed themselves to expenses of the leaves: the move of the adults happens in the late afternoon or toward evening.

When the rice field is submerged, the females go down below the hair of the water to put down the eggs.

After one period of incubation, whose lasted various in operation of the temperature, the larvas escape that, reached the roots, begin to feed being provoked the damages.

Struggle

The countries in which the Rice weevil is firmly present, have adopted programs of control of different nature: particularly they foresees the use of insecticides for the tanning of the seed, the use of tolerant cultivar and the practices agronomic recourse, what the delay of the submersion of the rice field. How measure of prophylaxis would be worthwhile to effect a control of the vegetation with important trofic resources for the adults to the beginning and at the end of the cycle of the rice cultivation.

Currently are not recorded relating to plant health products against such insect.