W. P. Scott

Seasonal Changes in Pyrethroid Resistance in Tarnished Plant Bug (Heteroptera: Miridae) Populations During a Three-Year Period in the Delta Area of Arkansas, Louisiana, and Mississippi

Abstract Tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), were collected from weeds at 71 locations in the delta of Arkansas, Louisiana, and Mississippi and tested with a discriminating dose bioassay for pyrethroid resistance in the spring (April–May) and again at the same locations in the fall (September–October) in 1995–1997. Percentage of mortality in the discriminating dose bioassay declined significantly (pyrethroid-resistance increased) from spring to fall by an average 18.7, 21.3, and 21.7% in Arkansas, Louisiana, and Mississippi, respectively. Pyrethroid resistance declined significantly by 26.3% from the fall of 1995 to the spring of 1996 in Mississippi, but did not significantly decline in Arkansas (4.1%) and Louisiana (13.2%). Significant decreases in resistance occurred in all 3 states from the fall of 1996 to the spring of 1997 (17.1, 38.3, and 29.8% in Arkansas, Louisiana, and Mississippi, respectively). Plant bugs from 2 locations (Indianola, MS, and Wainwright, LA) had multiple insecticide resistance to a carbamate, 2 pyrethroid, and 4 organophosphorus insecticides. However, resistance to the organophosphate acephate in plant bugs from both locations was not significant. Possible causes for the significant increases and declines in resistance from season to season are discussed.

Suppression of Tarnished Plant Bugs (Heteroptera: Miridae) in Cotton by Control of Early Season Wild Host Plants with Herbicides

Abstract Broadleaf weeds found in marginal areas by fields, roads, and ditches were controlled with herbicides in 23-km2 areas of the Mississippi Delta in March or April of 1999, 2000, and 2001. There were two treated and two untreated 23-km2 areas in each of the 3 test yr. The herbicides used were Trimec® or Strike 3™, and both contain mecoprop, 2, 4-D, and dicamba. Broadleaf weeds can serve as early season food and reproductive hosts for tarnished plant bugs, and population buildups can occur on these weeds before movement of plant bugs into cotton. Cotton fields in the treated sites and in untreated 23-km2 sites were sampled for tarnished plant bugs weekly during June and July of all 3 yr. Overall mean numbers of tarnished plant bugs were significantly lower in cotton in the treated areas. The average reduction in overall mean numbers of plant bugs was 50% for the 3-yr period. Grower costs for insecticides used to control plant bugs were lower in cotton in the treated test sites in all 3 yr. The average net savings in plant bug control costs was estimated at

Tarnished Plant Bug (Heteroptera: Miridae) Populations near Fields After Early Season Herbicide Treatment

35,477/yr for growers in the treated areas over the 3 yr of the study. Elimination of broadleaf weeds was found to be an effective method for reducing numbers of plant bugs in cotton. However, it did not reduce numbers of tarnished plant bugs in any year to a level in cotton where additional control with insecticides was not needed.

SCIENTIFIC NOTES EFFECT OF INSECTICIDE RESIDUES ON SURVIVAL OF MICROPLITIS CROCEIPES ADULTS (HYMENOPTERA: BRACONIDAE) IN COTTON

Abstract A single herbicide (Trimec® or Strike 3™) application in early season (March or April) was made to marginal areas around fields in 23-km2 test sites of the Mississippi Delta in 1999, 2000, and 2001. The herbicide was used to kill broadleaf weeds in the marginal areas that served as hosts for tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois). The herbicide treatment caused a significant reduction in wild host densities in the treated test sites in all 3 yr. Tarnished plant bug populations in treated test sites did not increase significantly in the treated marginal areas during April and May after treatment of the margins in the first 2 wk of March in 2000 and 2001. The herbicide application was made in the first 2 wk of April 1999, and plant bug populations increased in treated marginal areas in this year. The increase was thought to be caused by plant bugs moving to Italian ryegrass, Lolium multiflorum Lamarck, a previously unreported plant bug host, which was not affected by the herbicide. Laboratory tests showed that plant bugs would oviposit in flowering or nonflowering ryegrass when caged on ryegrass for a 6-d period. Newly emerged nymphs developed into adults (56%) when reared on floral spikelets of ryegrass, but no adults were obtained when they were reared on ryegrass stems and leaves. Rearing on floral spikelets beginning with third-instar nymphs resulted in 92% adults, whereas third-instar nymphs reared on stems and leaves produced no adults. These results showed that ryegrass could serve as a reproductive host for plant bugs when it flowered during late April and May. Application of the herbicide in March, when ryegrass was not in flower, resulted in no significant increases in plant bug populations on wild hosts (mainly ryegrass) during April and May in 2 yr of the field study.

Effect of ULV Malathion Use in Boll Weevil (Coleoptera: Curculionidae) Eradication on Resistance in the Tarnished Plant Bug (Heteroptera: Miridae)

A field test was conducted in August 1984 to determine the effects of thiodicarb (Larvin?), fenvalerate (Pydrin?), and flucythrinate (Pay-offs) residues on adult survival of Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), a common parasitoid of Heliothis spp. (Lepidoptera: Noctuidae) larvae. Preliminary topical tests demonstrated that these three insecticides were relatively non-toxic to adult M. croceipes. In the study presented here, five male and five female parasitoids (ages 1-4 d) were placed in each of 32 cylindrical cardboard cages (480 ml) constructed with organdy fabric at the ends, similar to those used by Scott and Lloyd (1975). Honey was provided as a food source. Three 2.0 ha plots of cotton within a 28.3 ha field were each treated with either thiodicarb (672.8 g AI/ha), fenvalerate (112.1 g AI/ha), or flucythrinate (44.9 g Al/ha), and one 2.0 ha plot remained untreated. Applications in a total volume of 37.3 1/ha were made using ground machinery. Immediately after treatment, eight cages each were placed at typical sites within each plot. Cages were attached to the terminal growth of a cotton plant such that wasps were allowed contact with the foliage. Four cages were removed from each plot 24 and 48 h after treatment and survival and mortality were recorded. Moribund wasps were recorded as dead, and wasps that escaped were not included in the calculation. A least squares two-way analysis of variance procedure was used to analyze the data. Across all treatments, significant differences (P<0.05) in survival did not occur between wasps observed at 24 and 48 h. Thus, the effects of any insecticide residues on survival were no greater at 48 h than at 24 h. High rates of survival (Table 1) indicated that M. croceipes tolerated residues of each of the insecticides tested. Survival was not significantly affected when flucythrinate residues were present on cotton. While residues of thiodicarb and fenvalerate induced only low levels of mortality in caged M. croceipes (Table 1), survival was significantly greater than that for the check. Apparently, M. croceipes was less tolerant of residues of thiodicarb and fenvalerate. Although fenvalerate was associated with the lowest rate of survival, this level would be