J. L. Bernhardt

Sampling Rice Stink Bug (Hemiptera: Pentatomidae) in and Around Rice Fields

Abstract Several sampling methods were used to determine the number of rice stink bugs, Oebalus pugnax (F.) in rice, Oryza sativa L., fields and grassy margins. Significantly more adult stink bugs were swept in fields of ‘Wells’ than ‘Francis’, ‘Cypress’, or ‘Bengal’. Sweep net sampling in the cooler parts of the day (0900 and 1900 hours CDT) captured significantly more rice stink bugs than in the heat of the day at 1330 hours CDT. In 2002, yellow pyramid traps were set out before rice heading. These traps captured more rice stink bugs from 5 June (before rice heading) to 12 July (75% rice heading) than during rice heading from 12 to 22 July. Significantly more rice stink bugs were visually counted on grass panicles and swept from grassy hosts in margins adjacent to rice fields from 28 June to 12 July than recorded after 12 July. During rice heading, rice stink bugs were dispersing into rice fields as noted by significantly greater counts of rice stink bugs per 10 sweeps in the rice field than at other rice growth periods sampled. After harvest, pyramid trap catches increased in late September to >20 bugs per trap but dropped to below 1 bug per trap after 3 October and to 0 by 1 November. In 2003, counts of rice stink bugs during the preheading, rice heading, and postheading periods from traps, sweep net samples of the field margins, and rice fields were similar to that in 2002. Pest sampling and management options are discussed.

Swimming Behavior of an Aquatic Weevil, Lissorhoptrus Oryzophilus (Coleoptera: Curculionidae)

The swimming behavior of the rice water weevil Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae) is unique in comparison to that of most other aquatic weevils. Propulsion during swimming is provided only by the mesothoracic legs. The legs are moved synchronously during protraction and retraction. The pro- and metathoracic legs serve as diving planes and provide stability. The average rice water weevil swimming speed was 1.53 (0.15 SE) cm per s with a range of 0.88 to 2.52 cm per s. Weevils averaged 5.67 (0.22 SE) strokes per s. The mode of swimming by L. oryzophilus differs from those described for Phytobious leucogaster (Marsham) (= Litodactylus leucogaster), P. comari (Herbst), Bagous cavifrons LeConte, B. americanus LeConte and B. limosus Gyllenhal. It also differs from descriptions of swimming for other aquatic Coleoptera and Hemiptera. Furthermore, L. oryzophilus swims below the surface and was observed at depths of 18.0 cm in the laboratory. This brings the modes of free swimming (exclusive of skating) to at least 3 by adult aquatic curculionids.

Antennal Sensory Structures of Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) with Notes on Aquatic Adaptations

Abstract A scanning electron micrograph study was conducted of adult Lissorhoptrus oryzophilus Kuschel to determine the types and locations of sensory structures on the antennae. The antenna consists of a scape, six-segmented funicle, and club. Females had significantly longer antennal segments than males, but no other sexually dimorphic characteristics were found. Trichoid sensilla, two types of squamaform sensilla, tuft hairs, and hydrofuge scales were found on the antennae. The distal third of the club was densely covered by trichoid sensilla that likely function in gustation and olfaction. Hydrofuge scales were on the antennal club, and plumose hydrofuge scales were on the rostrum. Squamiform sensilla were among the plumose hydrofuge scales on the rostrum. The information gained from this study may be used to design electrophysiological studies to provide information about the attractiveness of volatile compounds from rice plants and potential weevil pheromones. Aspects of the plastron of the weevil are also discussed. The antennae of rice water weevils have sensilla and hydrofuge adaptions for an aquatic environment and were found to be unique when compared to five species of terrestrial weevils.

Effect of Depth of Flooding on the Rice Water Weevil, Lissorhoptrus oryzophilus, and Yield of Rice

Abstract The rice water weevil, Lissorhoptrus oryzophilus (Kuschel) (Coleoptera: Curculionidae), is a semi-aquatic pest of rice and is the most destructive insect pest of rice in the United States. Adults oviposit after floods are established, and greenhouse studies have shown that plants exposed to deep floods have more eggs oviposited in leaf sheaths than plants exposed to a shallow flood. Experiments were conducted in three mid-southern states in the USA to determine if the depth of flooding would impact numbers of L. oryzophilus on rice plants under field conditions. Rice was flooded at depths of approximately 5 or 10 cm in Arkansas in 2007 and 2008 and Louisiana in 2008, and at depths between 0–20 cm in Missouri in 2008. Plants were sampled three and four weeks after floods were established in all locations, and also two weeks after flood in Missouri. On all sampling dates in four experiments over two years and at three field sites, fewer L. oryzophilus larvae were collected from rice in shallow-flooded plots than from deep-flooded plots. The number of L. oryzophilus was reduced by as much as 27% in shallow-flooded plots. However, the reduction in insect numbers did not translate to a significant increase in rice yield. We discuss how shallow floods could be used as a component of an integrated pest management program for L. oryzophilus.

Trapping Adult Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) with Aquatic Barrier Traps

Abstract The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is a pest of rice in the seven rice producing states of the United States and several countries where it has been introduced. Carbofuran was used adequately for nearly 30 yr, but it is no longer registered for use in rice and has been replaced by λ-cyhalothrin (Karate) and diflubenzuron (Dimilin). The scouting methods for carbofuran were inadequate or too late in determining the need for insecticide applications of the newer insecticides. Therefore, a new population monitoring method was developed using a double-ended aquatic barrier trap. The trap function was based on weevil swimming behavior, and 16 barrier trap prototypes were tested on adult weevils, 22–23 July 1998, in a small bay of late planted rice. Adult means ± SE were 73.9 ± 9.4 per trap on 23 July 1998 and 54.4 ± 6.4 per trap on 24 July 1998. The core sample mean for this plot was 72.9 ± 7.0 larvae per core. The trap was tested in both commercial fields and early and late planted small bays in 1999. Larval weevil infestations ranged from moderate (near or slightly below the economic injury level (EIL) to high (62.8 per core). Regression analyses showed a significant correlation between adults captured in traps to subsequent larval density in field edges (r2 = 0.98) and field interiors (r2 = 0.92). For every 1.0 rice water weevil adult captured in barrier traps, a density of 1.2–2.8 larvae per core sample was predicted. The aquatic barrier traps caught adult weevils without lures. Trapping rice water weevil adults immediately after permanent flood in drill-seeded fields can be used to aid decision making for insecticide application in rice.

Color Changes and Development of Eggs of Rice Stink Bug (Hemiptera: Pentatomidae) in Response to Temperature

ABSTRACT The progress of embryonic development may be observed in eggs of the rice stink bug, Oebalus pugnax (F.) (Hemiptera: Pentatomidae), because obvious color or color pattern changes may be viewed through the transparent chorion. All viable egg masses of the rice stink bug progressed through similar color or color pattern changes at the six constant temperatures that ranged from 21.1 to 37.8°C. Whenever the length of time within a pattern was expressed as a percentage of the total developmental time, the proportion of time within a pattern was not influenced by changes in temperature. However, temperatures used in this study were within the linear range for total development and within each color pattern of the rice stink bug eggs described in this article. The upper lethal constant temperature was estimated to be 37.8°C. Although phases of blastokinesis could be viewed, most were not related to color patterns in this study, except the katatrepsis phase, which is pictorially described. Rice stink bug egg masses consisted of two rows, the eggs being in contact but those of one row alternate in position with the other row. Embryos in both rows were oriented with the ventral surface toward the center of the egg mass.