Methoprene Research Articles

Disruption of oogenesis and molting by methoprene and glyphosate in Gammarus fossarum: involvement of retinoic acid?

In the last decade, the freshwater amphipod Gammarus fossarum proved to be a promising sentinel species in active biomonitoring programs to assess the effects of environmental contamination on non-target organisms. Given that the highly conserved retinoid (RETs) metabolism supports many biological functions and is perturbed by xenobiotics and used as biomarker for vertebrates, we explored the RETs functions in the crustacean model Gammarus fossarum. More specifically, we studied the implication of all -trans retinoic acid (atRA) in the reproduction (embryo, oocyte, and juvenile production) and development (success and delay of molting) by exposing G. fossarum females to atRA and citral (CIT), a known inhibitor of RA synthesis. In parallel, we exposed gammarids to methoprene (MET) and glyphosate (GLY), two pesticides suspected to interfere with atRA metabolism and signaling and frequently found in water systems. After 14days of exposure, atRA, CIT, and MET reduced the number of oocytes, whereas only MET caused a reduced number of embryos. After 44days, MET and GLY showed a tendency to decrease juvenile production. The duration of the molting cycle increased following the exposures to atRA and MET, while the treatment with CIT caused a typical endocrine disruptive inverted U-shaped curve. The exposure to GLY led to increased duration of the molting cycle at the lowest concentrations and lowered molting success at the highest concentration tested. This study highlights for the first time the implication of RA in the oogenesis and molting of G. fossarum and suggests that it may be a potential mediator of MET-induced effects on these processes. This study adds to the comprehension of the reproductive and developmental control in G. fossarum and opens new research avenues to study the effects of xenobiotics on the RET system in this sentinel species. Ultimately, our study will drive the development of RET-based biomarkers for non-target aquatic invertebrates exposed to xenobiotics.

The retinoid metabolism of Gammarus fossarum is disrupted by exogenous all-trans retinoic acid, citral, and methoprene but not by the technical formulation of glyphosate

Over the last decade, fluctuations of retinoids (RETs), also known as vitamin A and derivatives, have proved to be useful biomarkers to assess the environmental chemical pressure on a wide variety of non-target vertebrates. This use of RET-based biomarkers is of particular interest in the non-target sentinel species Gammarus fossarum in which RETs were shown to influence crucial physiological functions. To study and probe this metabolism in this crustacean model, a UHPLC-MS/MS method was developed to 1) identify and 2) monitor several endogenous RETs in unexposed females throughout their reproductive cycle. Then, females were exposed in controlled conditions to exogenous all-trans retinoic acid (atRA) and citral (CIT), a RA synthesis inhibitor, to simulate an excess or deficiency in RA. Perturbation of vitamin A metabolism by pesticides was further studied in response to methoprene (MET), a juvenile hormone analog as well as glyphosate (GLY). The developed method allowed, for the first time in this model, the identification of RA metabolites (all-trans 4-oxo and 13-cis 4-oxo RA), RA isomers (all-trans and 13-cis RA) as well as retinaldehyde (RALD) isomers (all-trans, 11-cis, and 13-cis RALD) and showed two distinct phases in the reproductive cycle. Retinoic acid successfully increased the tissular concentration of both RA isomers and CIT proved to be efficient at perturbating the conversion from RALD to RA. Methoprene perturbed the ratios between RA isomers whereas GLY had no observed effects on the RET system of G. fossarum females. We were able to discriminate different dynamics of RET perturbations by morphogens (atRA or CIT) or MET which highlights the plausible mediation of RETs in MET-induced disorders. Ultimately, our study shows that RETs are influenced by exposure to MET and strengthen their potential to assess aquatic ecosystem chemical status.

Susceptibility of stored grain insects to the insect growth regulator methoprene: Presentation

The insect growth regulator (IGR) methoprene is labeled in the United States (US) for direct application to stored grain commodities, and as a residual surface treatment to empty grain bins and flooring surfaces inside indoor structures. Methoprene is also labeled in the US as an aerosol for use in indoor areas. One of the challenges in research with methoprene and stored product insects is through design of experiments that mimic how methoprene would be used in practical applications. Recent research with methoprene will be used to describe experimental designs to examine efficacy of methoprene when used as a grain protectant.

STUDY OF QUANTITATIVE CHARACTERS BY SILKWORM LARVAE AFTER TOPICAL APPLICATION OF METHOPRENE AND FENOXYCARB

Juvenile hormone analogues have been tested as insect growth regulators in silkworm (Bombyx mori), seeking an increment of silk production. These chemical products, when applied in small or moderate rates, promote the extension of the last larval instar. In the cocoons and silk from 5th instar B. mori treated with selected doses of methoprene and fenoxycarb. Quantitative parameters like larval weight, silk gland weight , cocoon weight, cocoon shell weight, were determined. Methoprene and fenoxycarb influenced positively the duration of the fifth instar and the weight gain of the insects. Comparatively to the control lot, the increment on silk production was approximately 24% by the use of 1ng methoprene

Regulation of vitellogenesis in the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Studies were undertaken to investigate vitellogenesis and its regulation in female adults of the fall armyworm, Spodoptera frugiperda. A single female-specific protein, likely to be the S. frugiperda vitellogenin (Vg), appeared approximately 5 h after adult eclosion in the hemolymph of virgin females. The concentration of the protein increased with age as sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) revealed. A protein with the same relative molecular mass was also present in egg extracts, but absent from hemolymph samples from male moths. The relative molecular mass of the designated S. frugiperda Vg was determined as 164.5±2.5 kDa. Vitellogenic oocytes became visible 36–48 h after emergence and egg deposition began on day 3 of adult life. Vg could not be detected in the hemolymph of females decapitated directly after eclosion. When decapitated virgin females were injected with the JH-mimic methoprene (MP), the level of Vg was comparable to that in non-decapitated moths, indicating that vitellogenesis in S. frugiperda depends on juvenile hormone (JH). However, the number of vitellogenic oocytes was somewhat lower than in non-decapitated virgin females. Injection of 20-hydroxyecdysone (20E) promoted Vg production to a similar extent in decapitated female moths, but in contrast to methoprene injection, treatment with 20E never resulted in the production of vitellogenic oocytes. In vitro cultivated ovaries of adult females dissected directly after eclosion produced lower amounts of ecdysteroids than those isolated on day 1 after emergence. Our results suggest a crucial role for 20E in the induction of vitellogenesis in the noctuid S. frugiperda, while JH seems to be essential for the continued uptake of Vg by developing oocytes and may trigger 20E biosynthesis in the ovary.

Privatization of mosquito control services in urban areas.

Clarke Environmental Mosquito Management, Inc. is the largest privately-owned mosquito control company in the United States. Since 1946, Clarke has provided professional contract mosquito control services which are developed using a community-based, integrated mosquito management philosophy stressing environmental sensitivity and economic feasibility. The company is presently monitoring and controlling mosquitoes for over 250 communities, including most of Metropolitan Chicage, Illinois. In addition, Clarke provides complete programs for a number of small mosquito abatement districts ranging in size from 18-25 square miles. In general, the community programs are funded through municipal taxes and approved by the city councils. The mosquito abatement districts have a Board of Trustees which levies taxes and is responsible for overseeing the contract services. The advantages of private contracting in a community-based program include the ability to individualize a program to meet the local needs of the community and to provide quick response to problem areas. Private contractors are subject to annual reviews. Community leaders can assist in the course of action, making adjustments in the pro- grain strategy easier to implement. In addition, privatization can often result in considerable financial savings. For example, in northeastern Illinois the average cost of a fully staffed mosquito abatement district is $2.15 per citizen or $6,622.00 per square mile. In nearby DuPage County, a 338 square mile county which is covered primarity by a community-based private contractor, the cost is approximately $1.34 per citizen or $3,366.00 per square mile. In the State of Illinois, there are 55 mosquito species, two of which are of primary concern. The primary nuisance species is Aedes vexans. Although Ae. vexans presents no major public health hazard, broods of these vicious biting mosquitoes can migrate up to 20 miles and cause from 70 to 90% of the season's annoyance. The other species, Culex pipiens, the northern house mosquito, is recognized as the primary vector of St. Louis encephalitis (SLE) virus. Similar in many ways to Aedes aegypti, this mosquito develops in artificial containers, such as clogged roof gutters, tires, tin cans, vases and other water holding containers. The community-based programs developed by Clarke involve 5 components: General Services, Surveillance and Monitoring, Larval Control, Adult Control, and an Encephalitis Contingency Plan. Theoretically, a similar integrated program patterned after the Clarke program could be developed and initiated in collaboration with Health Department officials and community leaders for the control of Ae. aegypti and the prevention of dengue/DHF. For example, Part Ⅰ-General Services includes survey and mapping, public relations programs, a toll-free citizen response system, insurance coverage, monthly reports and quality control services, Part Ⅰ of an Ae. aegypti control program might include: defining the type and distribution of containers producing this species on private property; mapping of breeding areas on public property, providing staff social scientists and health educators to assist comunities in developing a source reduction plan; issuing monthly reports to community leaders and instituting quality control to assure program satisfaction. Part Ⅱ of our program, Surveillance and Monitoring, involves mosquito-borne disease monitoring through the collection of wild bird blood for laboratory testing for antibodies to SLE virus and the monitoring of Cx. pipiens populations in order to provide an early warning of the potential occurrence of human cases of SEE in northeastern Illinois. Similarly, Part II of an Ae. aegypti program could include continuous monitoring of Ae. aegypti populations and possible collection for virus isolation. Part Ⅲ-Larval Control, is the foundation of our program in Illinois and includes computer-based organization and classification of larval development sites. Larval control strategies are based on habitat type and the most appropriate control methodology, for example, stocking of mosquito fish (Gambusia offinis), treatment with B. t. i., methoprene, 5% temefhos (Abate) pellets or 5% Abate Tire Treatment. Part Ⅲ in the hypothetical Ae. aegypti control program would make the private contractor responsible for the development of a community-based program focusing on the individual citizen's role in vector control and the control and/or elimination of breeding areas, such as discarded tires and other large objects, on public property, Part Ⅳ-Adult Mosquito Management includes treatment of harborage areas where large numbers of mosquitoes congregate and spraying of residential areas during periods of excessive annoyance or an encephalitis alert. Adult mosquito control for Ae. aegypti might include house to house treatment of residential areas where dengue cases are detected. Part Ⅴ-The Encephalitis Contingency Plan, provides a contingency program using aerial application of adulticide when an SLE alert has been issued. Part Ⅴ of a Dengue Contingency Plan would outline a sequence of events the contractor would follow in the event of an encephalitis alert, this might include intensified mosquito surveillance, concentrated, community-wide information systems and area-wide adult mosquito control. The program under private contract would be evaluated annually and adjustments in the strategy would be implemented to ensure continuous improvement.

Evaluation of the control of mosquitoes with insect growth regulators.

In this study, the effectiveness of eight insect growth regulators (IGRs) (chlorfluazuron, diflubenzuron, EL-494, flufenoxuron, teflubenzuron, juglone, plumbagin and methoprene) against five mosquito vectors (Armigeres subalbatus, Aedes albopictus, Aedes aegypti, Culex tritaeniorhynchus, and Culex quinquefasciatus) was investigated in the laboratory. The EC50s of chlorfluazuron, diflubenzuron, EL-494, flufenoxuron, teflubenzuron, and methoprene against the five mosquitoes ranged from 0.0001 to 0.3 ppm and those of juglone and plumbagin from 3-25 ppm. The five mosquito species had similar tolerances to the test IGRs. At pH 5 to 9, the effectiveness of the first five chemicals was very stable. After ultraviolet irradiation or heat management (45 degrees C-60 degrees C), diflubenzuron and flufenoxuron were very stable. EL-494 was not stable when exposed to ultraviolet irradiation or heat. Under 0.1 ppm, teflubenzuron was not stable upon exposure to heat and chlorfluazuron and methoprene were not stable when exposed to ultraviolet irradiation. Piperonyl butoxide reduces the effectiveness of the five IGRs. Administration of diflubenzuron (1-5 ppm), flufenoxuron (0.025 ppm), and teflubenzuron (1-5 ppm) reduced Culex quinquefasciatus larvae in ditches by 40-90%. The administration of diflubenzuron (0.5 ppm) to containers reduced 97% of the Aedes albopictus larvae.

Activity of a Methoprene, Cyclopropane Miticide, and Resmethrin Formulation against Pests of Ornamentals

Activity of a Methoprene, Cyclopropane Miticide, and Resmethrin Formulation against Pests of Ornamentals