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Gut bacteria play important roles in the biology of insects. In this study, gut bacterial communities were investigated in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), which is a serious pest in rice growing-areas of the United States and some Asian countries. Overwintered female adults were collected from rice plants in five geographic locations: Beaumont, TX; Colt, AR; and Biggs, CA; in the United States, and Tanghai of Hebei and Yueqing of Zhejiang in China. Using polymerase chain reaction, bacterial 16S rRNA clone libraries were constructed. From the libraries, we identified 19 bacterial phylotypes (operational taxonomic units, OTUs). Of them, only 3–5 OTUs were identified in each population, except in the Beaumont weevils, which had 10 OTUs. The OTUs were affiliated with the bacteria in six classes of four phyla: α-, β-, γ-proteobacteria, Bacilli, Sphingobacteria, and Actinobacteria, with the γ-proteobacteria being the richest. Bacteria of the genera Pantoea and Wolbachia were detected in all weevil populations examined. There were also some bacteria that were specifically detected in certain locations but had a high relative abundance, such as the ones matched to Enterobacter oryzae, Lactococcus lactis, and Rickettsia felis. Geographic variations were found among bacterial communities in their richness, diversity, and evenness. This was the first study depicting a detailed profile of bacterial communities in L. oryzophilus, and the results provide important information for future studies on the bacterial functions, mutual interactions, and use for developing a biocontrol technique against this weevil.

Adults of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), were collected from three sources: 1) overwintering sites near rice, Oryza sativa L.; 2) a light trap placed in grassy vegetation and fallow fields; and 3) flooded rice plots near Beaumont, TX, from mid-April to late May 2005. Their color morph and reproductive status were surveyed. Frequency of the dark morph (36.0, 45.8, and 31.6% at each collection source, respectively) was significantly lower than that of the light morph (64.0, 54.2, and 68.4% respectively). Dark males accounted for only 3.5–7.4% of the populations, significantly less abundant than light males (28.8–32.0%) in each collection source. The morph frequency changed significantly with season in females, but not in males. Female-biased sex ratios were observed with the proportion of females to males being 1.5, 2.1, and 1.9 at each collection source, respectively. In most collections, ovarian development and mating status were similar between the females of different morphs, suggesting that elytral morph in this weevil might not be related to female reproductive development.

Based on atrophy of ovaries and hypertrophy of fat bodies, it is concluded that the rice water weevil, Lissorhoptrus oryzophilus Kuschel, overwintered in diapause in Louisiana. Weevils collected during Oct.–May and exposed to simulated summer conditions showed differences in duration of preoviposition and oviposition periods and in fecundity. More than 50% of weevils collected on or after the 3rd wk of Feb. oviposited, whereas less than 45% collected prior to this period oviposited. It is concluded that weevils were in diapause of variable intensity. About 1/7 of the overwintering females were mated and some contained resorbed eggs.

The small size and aquatic habits of the rice water weevil, Lissorhoptrus oryzophilus Kuschel, make observation difficult and, consequently, led early observers to make partially erroneous assumptions concerning the oviposition activity of the female and the location of the 1st-stage larvae. Early investigators reported that the female rice water weevil placed the egg longitudinally in the roots of the rice plant (Tucker 1912, Webb 1914, Ingram 1927, Isley and Schwardt 1930). The eggs reportedly hatched, and the larvae fed within the roots. This observation was partially correct, and the assumption was logical as the adults actually spend considerable time crawling around the base of the plant and sometimes enter the soil by crawling down the roots. In addition, 1st-stage larvae are frequently found in the roots. However, recent studies have shown that the eggs are inserted primarily (98.5%) in the submerged leaf sheath (Grigarick and Beards 1965, Everett 1965, Everett and Trahan 1967). Newly hatched larvae reportedly feed for a time in the leaf sheath and then crawl down the plant and enter the roots (Grigarick and Beards 1965). My recent observation confirms these reports with the exception that after hatching, the larvae apparently leave the exit hole and move by gravity through the water to the soil and roots. This observation agrees with Kuschel's (1951) statement that “the larva is ectophytic and because of the absence of locomotive appendages—which the dorsal spines replace very imperfectly—as in all members of the family, it can only move very slowly and in a dense medium like the mud of ponds.” Thus, the 1st-stage larvae are outside the plant and soil for a short time, and during this period the insect is in the most vulnerable stage in its life cycle.

Characters previously described for determining the sex of rice water weevils, Lissorhoptrus oryzophilus Kuschel, are either difficult to use or unreliable. Both Newell (1913) and Tucker (1912) reported that the females were slightly larger and more distinctly marked with black than the males. The color pattern is usually obscured by scales, dirt, or algae, however, and Newell (1913) did not consider it a useful character for sex determination. W. D. Pierce was reported by Newell (1913) and Tucker (1912) as having made a study of secondary sexual characters. From this study, Pierce determined that the antennal scrobe on the beak was slightly curved in the female and straight in the male. Because of the curvature of the beak, this character is difficult to use and may result in errors of judgment. At best, it is useful for restricted numbers of weevils and then only after careful study and practice.