Efficacy of ground-applied ultra-low-volume malathion on honey bee survival and productivity in open and forest areas.

A study was conducted to determine the efficacy of ground ultra-low-volume malathion sprays on honey bee (Apis mellifera L.) apiaries in open and forested areas downwind from the spray route. Impact on colonies 7.6, 15.2, 47.7, and 91.4 m downwind from sprays was assessed by recording individual bee mortality 12 and 36 h after treatment. In addition, hives were weighed before as well as during the study and cluster counts were conducted at each hive to determine colony strength before and after treatment. Spray drift was monitored by the use of caged mosquito (Culex quinquefasciatus Say) mortality and deposition on filter paper. During the study, significant bee mortality in the open area occurred on 2 occasions at 7.6 m (16.8 +/- 4.3 bees, 11.8 +/- 7.0 bees) and at 15.2 m (6.5 +/- 1.7 bees, 5.3 +/- 1.5 bees). Significant mortality in the forested area was observed only once and consisted of 2 bees at 7.6 m. In each case where bee mortality occurred, spray deposits on filter papers had exceeded 400 ng/cm2. Although mortality of caged mosquitoes indicated that malathion drifted through the study areas, little correlation was apparent between mortality and spray deposition on filter paper.

Impacts of Dibrom concentrate and three new naled formulations on three 1996 Du Pont automotive paint finishes.

To investigate potential impacts on automobile finishes, droplets of 4 naled formulations were applied to 3 contemporary automotive paints and assessed by means of microscopic and unaided visual inspections. Three droplet size ranges simulated ground- and aerial-based ultra-low volume applications and were each generated for Dibrom Concentrate, a new formulation of Dibrom Concentrate (VC-1088), and two other new naled formulations (Trumpet VC-1083 and Trumpet VC-1084). Du Pont automotive paint finishes tested were RK7072, RK8010, and RK7120 used on Ford trucks, General Motors cars, and Cadillacs, respectively. Visible spotting was never produced by small droplets averaging (SE) a volume median diameter of 13.12 microns (0.44), and quantifiable microscopic spots were detected only on the RK8010 paint finish. The latter paint finish was the most susceptible to spotting, whereas RK7072 was not affected by any formulation at each droplet size.

Half-life of naled under three test scenarios.

Decline of naled residue on filter paper was studied after exposure to ultra-low volume droplets in a settling chamber. Naled-treated filter papers were stored under 3 treatment scenarios: 1) in a dark environmental chamber at an average relative humidity (RH) of 46.9% and temperature of 24 degrees C, 2) in a dark environmental chamber at an average RH of 87.7% and temperature of 24 degrees C, and, 3) in direct sunlight in the field. Decline of naled followed first order kinetics in all cases; consequently, half-life of naled under each treatment was determined from the slope of each line. Half-life (+/- 1 SD) of naled was 8.17 +/- 1.24, 4.81 +/- 1.18, and 1.37 +/- 0.24 h, for treatment scenarios 1, 2, and 3, respectively. In each test, a significant (P < 0.05) decline in naled residue occurred between initial assessment and 4 h postapplication. The half-life of each treatment scenario was significantly (P < 0.05) different from that of the other 2 scenarios, indicating that both humidity and sunlight affect naled degradation rates.

Acute effects of Permanone 31-66 (permethrin-piperonyl butoxide) on nontarget minnows and grass shrimp.

Immature sheepshead minnows (Cyprinodon variegatus), inland silversides (Menidia beryllina), mosquitofish (Gambusia holbrooki), and grass shrimp (Palaemonetes pugio) were exposed to the mosquito adulticide, Permanone 31-66, in a series of static toxicity tests conducted in the laboratory. At 24 h, in order of decreasing susceptibility, LC50 values were 0.843, 4.07, 5.46, and 6.04 ppb for grass shrimp, inland silverside, sheepshead minnow, and mosquitofish, respectively. Forty-eight-hour LC50 values for grass shrimp, inland silverside, sheepshead minnow, and mosquitofish were 0.049, 2.86, 3.02, and 4.29 ppb, respectively.

Integrated management of waste tire mosquitoes utilizing Mesocyclops longisetus (Copepoda: Cyclopidae), Bacillus thuringiensis var. israelensis, Bacillus sphaericus, and methoprene.

This study evaluated the compatibility and efficacy of using a predatory copepod, Mesocyclops longisetus in concert with 3 "biorational" compounds for mosquito control in waste tires. The toxicity of Bacillus thuringiensis var. israelensis (B.t.i), Bacillus sphaericus, and methoprene to Mesocyclops longisetus was assessed in the laboratory using concentrations 10 times the maximum labeled or suggested rate and based on a water depth of 7.6 cm. Microbials were tested using mature copepods exposed for durations of 24, 48, and 72 h. Methoprene bioassays consisted of individually exposing newly hatched copepods (i.e., nauplius larvae) and monitoring their development to maturity. The toxicity tests indicated B.t.i., B. sphaericus, and methoprene were not deleterious to copepods at concentrations exceeding those expected in the field. Copepods exposed to methoprene matured normally, and when mated, 50% developed egg sacs. A 5-month field test, integrating the copepod and B.t.i., B. sphaericus, and methoprene provided better mosquito reduction together than either copepods or control agents alone. When copepods were combined with B.t.i. or methoprene, overall reduction of 3rd- and 4th-instar larvae during the 5-month interval was equal to or greater than 90%. Bacillus thuringiensis var. israelensis alone temporarily produced a high degree of larval reduction (up to 100%), however reapplications were necessary to maintain that level of control. Of all the treatments, B. sphaericus alone produced the lowest degree of mosquito suppression due to lack of toxicity to Aedes albopictus, the predominant species during the study. It is recommended that mosquito control managers consider integrating M. longisetus and B.t.i. or methoprene against mosquitoes in waste tires.

Tolerance of sewage treatment plant microorganisms to mosquitocides.

Beneficial protozoa and rotifers collected from a wastewater treatment plant in Panama City, FL, were tested for tolerance to 11 commonly used mosquito larvicides and adulticides in the laboratory. The acute effects were assessed using selected concentrations of the adulticides fenthion, malathion, naled, permethrin, and resmethrin; and the larvicides Bacillus thuringiensis israelensis, Bacillus sphaericus, diflubenzuron, larviciding oil, methoprene, and temephos for the following microorganism taxa: ameoboids, flagellates, free-swimming ciliates, stalked ciliates, and rotifers.

Susceptibility of first instar Toxorhynchites splendens to malathion, naled and resmethrin.

Acute toxicity tests were conducted to measure the response of first instar Toxorhynchites splendens to commonly used mosquito adulticides: malathion, naled and resmethrin. The concentrations of pesticide causing 50% mortality (LC50) after 24 h was 2.87, 69.1 and 623 ppb for resmethrin, malathion and naled, respectively. Naled was determined to be the least toxic of the 3 compounds tested for integrated use with Tx. splendens. The latter assessments were based on comparisons between laboratory-derived dose-response curves and maximum concentrations reached in standing water calculated using standard application rates.

Effect of ULV malathion on automotive paint finishes.

The relationship between malathion droplet size (VMD) and degree of damage to 1990, 1K and 2K General Motors paint standards was investigated in the laboratory and field. Laboratory tests indicated a positive correlation between malathion droplet VMD and damage spot size. Laboratory settling chamber tests revealed that size-thresholds of droplets too small to cause visible damage averaged 8 and 11 mu on washed 1K and 2K paints, respectively. Field tests indicated malathion caused no visible damage to 1K or 2K paint panels under routine operating conditions, although droplet sizes (VMD) sampled on the automobile surface averaged 10.2 +/- 4.5 and 11.7 +/- 5.7 mu. Microscopic damage was found on paint panels placed on the hood, roof, trunk and doors of the automobile when parked parallel or perpendicular to the course of the spray truck and when driven through the spray of a stationary spray truck.

Acute toxicity of mosquitocidal compounds to young mosquitofish, Gambusia affinis.

Toxicity of Florida mosquito larvicides and adulticides to 3-5 day old Gambusia affinis was determined in the laboratory. After 24-h exposure, the larvicides, temephos, fenoxycarb and petroleum distillates had LC50 values of 5.60, 1.05 and 593.4 ppm, respectively. After 24 h the adulticides resmethrin, fenthion, naled and malathion had LC50 values of 0.007, 2.94, 3.50 and 12.68 ppm, respectively. The only compound toxic to young mosquitofish at maximum field application rates was resmethrin. However, in the light of earlier tests, aerially applied adulticides generally reach the water surface at reduced concentrations and thus probably pose little or no risk to mosquitofish populations.

Biological control of Culex mosquitoes (Diptera: Culicidae) by the tadpole shrimp, Triops longicaudatus (Notostraca: Triopsidae).

Laboratory oviposition choice tests and behavioral observations indicated that the activity of tadpole shrimp, Triops longicaudatus (LeConte), near the water surface deterred gravid Culex quinquefasciatus Say from ovipositing. In the cities of Oasis and Riverside, Calif., tadpole shrimp significantly reduced the abundance of immature mosquitoes (Cx. tarsalis Coquillett and Cx. quinquefasciatus) probably due to lowered oviposition rates, as well as tadpole shrimp predation. Generally, mosquito oviposition rates in field ponds with tadpole shrimp were lower than that of controls, except when tadpole shrimp were very young (4 d after flooding) or when their abundance had declined late in the flooding period. When analyzed by pond, tadpole shrimp size was correlated inversely with abundance; however, differences in size or abundance did not affect their capacity to reduce mosquito populations.

Influence of tadpole shrimp, Triops longicaudatus (Notostraca:Triopsidae), stocking rate on Culex tarsalis development in experimental field microcosms.

The effectiveness of 5 tadpole shrimp (TPS) stocking rates to reduce cohorts of Culex tarsalis was studied in field microcosms (0.81-m2). Larval/pupal abundance in microcosms containing greater than 5 TPS/m2 was significantly (P less than 0.05) lower than that of controls lacking tadpole shrimp due to predation. Adult mosquito abundances captured in emergence units above the microcosms stocked with tadpole shrimp were significantly (P less than 0.05) lower than that of controls at rates greater than or equal to 10 TPS/m2. Tadpole shrimp growth during 17 days of this study was inversely proportional to their stocking rate, and a linear relationship between size and stocking rate was plotted. Tadpole shrimp stocking rates also influenced rate of mosquito development, causing significantly (P less than 0.05) shorter periods for 50% emergence where shrimp were present when compared with that of controls. Adult male Cx. tarsalis emerged significantly earlier then females in microcosms stocked at 5 TPS/m2, while no significant (P greater than 0.05) differences were detected between the sexes at the remaining predator stocking rates.

Ecology of Culex tarsalis (Diptera: Culicidae): factors influencing larval abundance in mesocosms in southern California.

Colonization and succession of mosquitoes and macroinvertebrate predators were studied in 30-m2 ponds (mesocosms) during summer and fall 1987. Larval abundance of Cx. tarsalis Coquillette was lower during the hot, summer months than during the fall. In all studies, larval populations declined markedly 2-3 wk after habitat flooding. Although predator abundances differed in these studies, sometimes by an order of magnitude, the common predators colonized mesocosms in the following order: Triops, hydrophilid beetle larvae, dytiscid beetle larvae, mesoveliids, dragonfly and damselfly naiads, and notonectids. The similarity of the colonization phenologies probably resulted from the vagility of the adult insects and species-specific developmental rates. Stepwise multiple regression was used to identify factors potentially affecting larval mosquito populations. For most studies, coleopteran larvae were related inversely to per capita change in the entire larval population and the third- and fourth-instar subpopulation (i.e., large coleopteran larval populations were associated with large declines in the Cx. trasalis larval population). Maximum water temperatures and pond age (days after flooding) also were identified as significant factors affecting larval abundance and per capita change of mosquitoes. Potentially lethal water temperatures (greater than or equal to 35 degrees C) occurred during the summer; however, the declines in larval abundance of Cx. tarsalis were not restricted to (or obviously associated with) periods of high water temperature. Our results indicated that predation by coleopteran larvae and factor(s) associated with pond age, such as mosquito ovipositional preferences, significantly affected Cx. tarsalis larval populations.

Prey-size selection by Triops longicaudatus (Notostraca: Triopsidae) feeding on immature stages of Culex quinquefasciatus.

The tadpole shrimp, Triops longicaudatus, was found to be a size-dependent predator of Culex quinquefasciatus larvae in the laboratory. However, changes in tadpole shrimp size were accompanied by changes in prey-size preference: larger-sized predators consumed an increasing proportion of larger prey items. Very large tadpole shrimp may be nonselective predators of this mosquito species. Quantified behavioral observations indicated that while second instar mosquito larvae were encountered significantly less frequently than were fourth instar larvae or pupae, they were captured at significantly greater rates and with shorter handling times. It is hypothesized that prey vulnerability has an important influence on tadpole shrimp prey size "preferences."

Efficacy of Bacillus sphaericus 2362 formulations against floodwater mosquitoes.

Four new formulations of Bacillus sphaericus 2362 yielded excellent control of floodwater mosquitoes Psorophora columbiae and Aedes nigromaculis in irrigated fields in Kings and Riverside counties of California. A primary powder formulation (ABG-6184) was the most active, producing excellent control of Ps. columbiae and Ae. nigromaculis at the rates of 0.05 to 0.5 lb/acre (0.055-0.56 kg/ha). A liquid formulation (BSP-2) was slightly less active, but was effective against the same species in the range of 1.0-1.5 lb/acre (1.12-1.68 kg/ha). Activity of the two corn cob granular formulations was largely dependent on potency (spores/gram). The high spore count granules (1.5 x 10(9) spores/gram) yielded 91 and 98% reduction of Ae. nigromaculis at the rates of 2.5 and 5.0 lb/acre (2.8 and 5.6 kg/ha), respectively. Against the same population, the lower spore count formulation (7.6 x 10(8) spores/gram) produced complete control at the rate of 10 lb/acre (11.2 kg/ha), but poor results were obtained at the rate of 5 lb/acre (5.6 kg/ha).