Response of Water-Seeded Rice to Insecticidal Control of Target and Non-Target Aquatic

The objectives of this research were: 1) determine if selected non-target, aquatic insects are responsible for uprooting rice seedlings, 2) determine if these insects are affected by the insecticides fipronil (Icon 6.2FS) and lambda-cyhalothrin (Karate Z) applied in different planting regimes to control rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), and 3) evaluate the effectiveness of these insecticides against the RWW.

Materials and Methods

Field research included water-seeded rice planted in 2003 and 2004 utilizing continuous and pin-point flood regimes. Each year, one experiment was conducted under a continuous flood regime and one under a pin-point flood regime. All experiments were designed as split-plots with main plots of dry or presprouted seed and sub plots of Icon 6.2FS-treated, Karate Z-treated or untreated (Fig. 1). Data collected included numbers of dead insects from the water surface following seeding, numbers of floating rice seedlings (floaters), numbers of live insects from the water column and soil surface, numbers of immature RWW and yield. Based on personal observations in the field, adult Tropisternus lateralis (Say) (Coleoptera: ) bring rice seedlings to the water surface. Two greenhouse experiments were conducted with varying densities of adult T. lateralis and another abundant hydrophilid , infuscatus LeConte. Both experiments were designed as randomized complete blocks with 4 treatments and 5 replications. The first greenhouse experiment investigated T. lateralis at four densities: low (1 individual); middle (3 ind.); high (5 ind.); and control (0 ind.). The second experiment was similar to the first but bins were infested with B. infuscatus at higher densities: low (2 ind.); middle (6 ind.); high (10 ind.); and control (0 ind.). Floaters were collected daily for 10 days following infestation and plant stands were obtained from each bin.

I II III IV Icon 6.2FS Icon 6.2FS Karate Z Untreated Karate Z Karate Z Untreated Karate Z Untreated Untreated Icon 6.2FS Icon 6.2FS Icon 6.2FS Karate Z Untreated Untreated Karate Z Icon 6.2FS Icon 6.2FS Karate Z Untreated Untreated Karate Z Icon 6.2FS

Dry seed Presprouted seed

Figure 1. Plot plan for field experiments. Four replications (I, II, III and IV) of 6 treatments. Main plots are seed type: unshaded plots are dry seed, shaded plots are presprouted seed. Subplots are insecticide application: Icon 6.2FS, Karate Z and untreated. Beaumont, TX. 2003 and 2004.

Results and Discussion

Field experiments: In 2003, Karate Z was applied before flooding and resulted in high numbers of dead insects on the water surface. In 2004, Karate Z was not applied until rice emergence through the water surface; thus, dead insects collected before Karate Z application were less numerous compared to 2003. Applications of the insecticides Icon 6.2FS and Karate Z (when applied before flood) resulted in large numbers of dead insects as well as reductions in numbers of uprooted seedlings or floaters (Fig. 2). This suggests that one or more aquatic species affected by the treatment insecticides were responsible for uprooting seedlings. Icon 6.2FS appeared to be less effective than Karate Z in controlling RWW. Data suggest seeding a field immediately after flooding before aquatic, non-target insects have extensively colonized the field, and utilizing a pin-point rather than a continuous flood reduce floaters. Timing of insecticide applications seems to be crucial to controlling non-targets responsible for uprooting seedlings. 140 1200 Dry Presprouted A B 120 1000 Dry 100 Presprouted 800 80 600 60 No. floaters No. floaters No. 400 40

20 200

0 0 Continuous Pin-point Continuous Pin-point Flood regime Flood regime

1600 200 Icon 6.2FS Karate Z C D Untreated 1400 a Icon 6.2FS a 1200 Karate Z 150 a 1000 a Untreated 800 100 600 No. floaters No. floaters 400 50 b b b c 200 a b b ab 0 0 Continuous Pin-point Continuous Pin-point Flood regime Flood regime

Figure 2. Total floaters in main plots and in subplots for continuous and pin-point flood experiments in 2003 (A and C) and 2004 (B and D). Beaumont, TX. In each flood regime, bars with the same or no letter are not significantly different (P > 0.05, LSD). Greenhouse experiments: Results showed that T. lateralis uprooted seedlings but B. infuscatus did not. Bins containing the high density of T. lateralis had significantly lower stands than low and control densities (Fig. 3). Floaters were not detected in B. infuscatus bins. In water-seeded plantings, particularly a continuous flood, T. lateralis can be a stand-reducing pest. Other aquatic, non-target insects may be involved in rice stand reductions, but further studies are needed to better define this possibility. Historically, rice farmers practicing water-seeding have blamed poor stands on a variety of abiotic and biotic factors, not including T. lateralis. This research has identified another biological agent responsible for dislodging rice seedlings. Further research is needed to determine the role of gender, mating and foraging on uprooting of rice seedlings by T. lateralis. In addition, commercial size field experiments should be conducted to determine stand losses caused by T. lateralis or other aquatic, non-target insect(s).

45 40 No. T. lateralis /bin A 0 1 3 5 a 35 30 25 a b 20 a

No. floaters 15 ab 10 c a a b a 5 bc b a b bc c b 0 b* b* b* c* c* b* ** * 4 5 6 7 10 11 13 Days after seeding

100 180 B C 90 160 a a 80 a 140 a 70 120 60 b 100 50 b 80 40 No. floaters 60

30 (plants/bin) Stand 20 c 40 10 20 c 0 0 No. T. lateralis per bin No. T. lateralis per bin

Figure 3. Number of floaters per days after seeding (A), number of floaters per treatment (B), and stand per treatment (C) for greenhouse experiment 1. Beaumont, TX. 2004. For each day after seeding in A, bars with no letter are not significantly different (P > 0.05, LSD). No floaters collected where indicated (*).