Biological, Ecological, and Morphological Investigations of the Rice Water Weevil, Lissorhoptrus Oryzophilus Kuschel, on Two Rice Genotypes.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important insect pest of rice, Oryza sativa (L.), in the United States. Although this insect has been associated with O. sativa since the introduction of this plant species into the United States in 1685, some aspects of its biology remain obscure. Larvae of L. oryzophilus have four instars, based on measurements of head-capsule widths of field-collected larvae in 1981 and 1982. The head-capsule widths of each instar were: I, 0.14 to 0.18 mm; II, 0.20 to 0.26 mm; III, 0.28 to 0.38 mm; IV, 0.40 to 0.60 mm. Further studies revealed that the duration of each instar was: I, 1.20; II, 2.56; III, 7.14; and IV, 10.33 days, respectively at 27.1 (+OR-) 5.6(DEGREES)C. Plant introduction PI 321264 sustained significantly (p \u3c 0.01) lower larval populations of L. oryzophilus and was significantly (p \u3c 0.01) less preferred for feeding than the susceptible variety Saturn. Populations of L. oryzophilus larvae appear to conform to a clumped distribution pattern. Sampling plans using the equation: log(,e)T(,n) = (log(,e)(D(,o)(\u272)/a)/b - 2) + (b - 1/b - 2)log(,e)n, show that 15 samples of Saturn and 19 samples of PI 321264 are needed to estimate L. oryzophilus larval populations with a relative variance of 10%. Scanning electron microscopy of the antenna and venter of L. oryzophilus revealed bifurcate sensilla trichodea, sensilla basiconica, and sensilla placodea on the antennal club. All three sensilla types were also found on the rostrum. Brush-like sensilla were found on the rostrum, legs, coxae and abdominal sternites VI and VII. All receptor types are found to be distributed similarly on both males and females. Females possess significantly (p \u3c 0.01) more sensilla basiconica and longer sensilla placodea than males