Impact of naled on honey bee Apis mellifera L. survival and productivity: aerial ULV application using a flat-fan nozzle system.

A study was conducted to evaluate the impact of naled on honey bees as a result of their exposure to aerial ULV applications of this insecticide during three routine mosquito spray missions by Manatee County Mosquito Control District in Florida during the summer of 1999. Naled deposits were collected on filter paper and subsequently analyzed by gas chromatography. Mortality of adult honey bees Apis mellifera L. was estimated based on numbers from dead bee collectors placed in front of the entrance of the beehives. We found that honey bees clustering outside of the beehives were subject to naled exposure. Bee mortality increased when higher naled residues were found around the hives. The highest average naled deposit was 6,227 +/- 696 microg/m2 at the site 1 forest area following the mosquito spray mission on July 15, 1999. The range of naled deposition for this application was 2,818-7,101 microg/m2. The range of dead bees per hive was 0-39 prior to spraying and 9-200 within 24 h following this spray mission. The average yield of honey per hive was significantly lower (p < 0.05) for naled-exposed hives compared with unexposed hives. Because reduction of honey yield also may be affected by other factors, such as location of the hives relative to a food source and vigor of the queen bee, the final assessment of honey yield was complicated.

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.

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.

Downwind drift and deposition of malathion on human targets from ground ultra-low volume mosquito sprays.

Malathion was sprayed using a truck-mounted ultra-low volume (ULV) aerosol generator. The generator was operated at 41.4 kPa (6 psi) at flow rate of 128 ml (4.3 fl. oz.) per min. Malathion concentrations were measured at selected positions on live, stationary human subjects wearing protective clothing and placed along a transect at right angles to the path of the truck. Two standing subjects were exposed downwind to the malathion spray at 7.6 and 15.2 m. A third subject was exposed while jogging in the same direction as the spray vehicle and 1.5 m from the spray path. No significant differences (P > 0.05) in total amount of malathion deposited on subjects was demonstrated. During the last 4 sprays, average amounts of malathion deposited on ground level at 15.2, 30.4 and 91.2 m were not significantly different (P > 0.05). Malathion dermal residues were compared with the acute LD50 value (4,100 mg/kg) for a 70 kg adult male. Calculated malathion dermal exposures were less than the acute lethal dose for a human subject by 4 orders-of-magnitude or more.

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.

Effects of Arosurf MSF on a variety of aquatic nontarget organisms in the laboratory.

Ninety-six-hour static acute toxicity tests were conducted in the laboratory to determine the effects of a 47 ml/m2 (50 gal/acre) application of Arosurf MSF (2 mole ethoxylate of isostearyl alcohol) on Fundulus similus, Palaemonetes pugio, Palaemonetes paludosus, Uca spp., Procambarus spp., Gammarus spp., Asellus spp., Streptocephalus seali, Physa spp., Laeonereis culveri and an unidentified amphipod. Test temperatures of 20-27 degrees C were based on the ambient water temperature for the season of the year when the desired life stages were more abundant. No acute toxicity was observed with any of the organisms exposed to this concentration of Arosurf MSF.

Effects of pressure and flow rate on Cythion droplet size produced by three different ground ULV aerosol generators.

A study to determine the effects of machine pressure and insecticide flow rate on the size of aerosol droplets as they relate to the Cythion label was conducted with 3 different ground ULV aerosol generators. An increase in flow rate required a corresponding increase in blower pressure to maintain the labeled droplet mass median diameter of 17 microns or less. Droplets larger than 48 microns were frequently sampled at machine pressures less than 6 psi (41.4 kPa). At the highest labeled flow rate of 8.6 fl oz/min (254.3 ml/min), machine pressures of 7-8 psi (48.3-55.2 kPa) were required for each of the 3 aerosol generators tested to consistently conform to the droplet criteria of the Cythion label.

Preliminary data on use of the inland silverside, Menidia beryllina, to control mosquito larvae.

A study of procedures for spawning and culture of the inland silverside, Menidia beryllina, was conducted. The efficacy of young Menidia, 20 to 22 and 31 to 33 days old, to control mosquito larvae was determined in the laboratory with first and second larval instars of the saltmarsh mosquito Aedes taeniorhynchus. Feeding trials were run at salinities of 1, 5, 15 and 25%. Field trials were also conducted to determine if Menidia would effectively control Culex quinquefasciatus in brackish water impoundments.