Effects of three chitin synthesis inhibitors on egg masses, nymphs and adults of Halyomorpha halys (Hemiptera: Pentatomidae)

BACKGROUND

Halyomorpha halys, (brown marmorated stink bug, BMSB), is a high-concern invasive species causing severe damage to orchards in many countries outside its native Asian range. Management methods other than frequent sprays of broad-spectrum insecticides are needed to restore integrated pest management (IPM) practices in orchards. Chitin synthesis inhibitors are usually regarded as desirable options in IPM programs because of lower toxicity to beneficial insects and non-target organisms compared to neurotoxic insecticides. In this study, the activity of three chitin synthesis inhibitors (namely buprofezin, novaluron and triflumuron) was investigated on BMSB egg masses, third instars and adults by means of laboratory bioassays.

RESULTS

Novaluron and to a lesser extent triflumuron were detrimental to BMSB nymphs exposed to residues on potted peach plants. Novaluron caused high mortality among early instars that emerged from sprayed egg masses. No significant differences were found between buprofezin and water control on eggs or third instars. When sprayed on BMSB adults, none of the chitin synthesis inhibitors affected survival, fecundity, or egg hatching.

CONCLUSION

Given the activity on nymphs, but the lack of effects on adults, novaluron and triflumuron might be considered for field applications only as a tool in a wider management strategy along with other methods aimed at preventing the invasion of crops by BMSB adults. © 2023 Society of Chemical Industry.

A Novel Enantioseparation Method and Enantioselective Dissipation of Novaluron in Tomatoes Using Ultrahigh-Performance Liquid Chromatography Tandem Mass Spectrometry via a Box-Behnken Design

Enantioseparation parameters of novaluron were optimized on a Chiralpak IG-3 column by ultrahigh-performance liquid chromatography tandem mass spectrometry via response surface methodology. The absolute configuration and elution order were identified as R-(+)-novaluron and S-(-)-novaluron by polarimetry and X-ray diffraction. A modified QuEChERS method was developed for enantioselective determination of novaluron in eight food and environmental samples. Under optimal conditions, the mean recoveries of the novaluron enantiomers in the eight matrices were 74.4-108.1% with intraday relative standard deviations (RSDs) of 0.3-9.7% and interday RSDs of 0.1-4.1%. Enantioselective dissipation was observed in tomatoes. The dissipation of S-(-)-novaluron was faster than that of R-(+)-novaluron with a half-life of 7.1 and 7.9 days, and the enantiomer fraction value changed from 0.49 to 0.53 in 21 days. An effective method for monitoring novaluron enantiomer residues in food and the environment was established for the first time and had been successfully applied to real samples. This study is of great significance for strengthening the risk assessment and supervision level of chiral pesticides.

Insect growth regulators elicit transovarial effects on Teleonemia scrupulosa (Hemiptera: Tingidae)

BACKGROUND

Lantana lace bug, Teleonemia scrupulosa Stål (Hemiptera: Tingidae), is an important insect pest of lantana (Lantana camara L.). The adults and nymphs feed on the leaves, gradually deteriorating the quality of leaf tissue, as the affected leaves appear brown and desiccated. Infestations of T. scrupulosa reduce the market value of container plants in nurseries and the aesthetic value of ornamental landscapes. Because T. scrupulosa typically is managed using neonicotinoids and concerns related to the nontargeted effects of neonicotinoids on pollinators are mounting, practitioners are seeking alternative options to manage T. scrupulosa infestations. Insect growth regulators (IGRs) elicit transovarial activity, where adults exposed to IGRs produce nonviable eggs, but this effect has not been documented for T. scrupulosa.

RESULTS

A significantly lower number of T. scrupulosa nymphs was produced when adults were sprayed topically with novaluron and pyriproxyfen than nontreated adults. The number of T. scrupulosa nymphs produced was not significantly different when adults were exposed to a lower dose (0.125×) and a maximum dose (1.0×) of novaluron.

CONCLUSION

Novaluron and pyriproxyfen elicited transovarial effects on T. scrupulosa when adults were exposed to these IGRs. Evidence of transovarial effects was demonstrated when T. scrupulosa adults were exposed to lower doses (≤0.125×) than the maximum label dose, as densities of nymphs were similar between the lower doses and the maximum label dose of novaluron.

Review of the existing maximum residue levels for novaluron according to Article 12 of Regulation (EC) No 396/2005

According to Article 12 of Regulation (EC) No 396/2005, EFSA has reviewed the maximum residue levels (MRLs) currently established at European level for the pesticide active substance. Although this active substance is not authorised within the European Union, MRLs were established by the Codex Alimentarius Commission (codex maximum residue limits; CXLs) and import tolerances were reported by Member States and the UK (including the supporting residues data). Considering that no toxicological reference values are currently established in Europe for novaluron because the peer review for the approval was terminated before an EFSA conclusion was issued, the toxicological profile of novaluron was also assessed, in order to be able to perform the consumer risk assessment in the framework of the art 12 MRL review. Based on the assessment of the available data, toxicological reference values were derived, and a consumer risk assessment was carried out for the existing CXLs and import tolerances. All CXLs and import tolerances were found to be supported by inadequate data and a possible chronic risk to consumers was identified. Hence, further consideration by risk managers is needed.

Novaluron Has Detrimental Effects on Sperm Functions

Although novaluron is an insect growth regulator with a low mammalian acute toxicity and a low risk to the environment and nontarget organisms, toxic effects of novaluron have been reported. However, no studies have yet evaluated the effect of novaluron on reproduction. Therefore, we examined the effects of novaluron on sperm functions. The spermatozoa of ICR mice were incubated with various concentrations of novaluron to induce capacitation. Then, sperm motion parameters and capacitation status were evaluated using CASA program and H33258/chlortetracycline staining. In addition, PKA activity and tyrosine phosphorylation were evaluated by Western blotting. After exposure, various sperm motion parameters were significantly decreased in a dose-dependent manner. The acrosome reaction was also significantly decreased in the high concentration groups. Sperm viability was significantly reduced at the highest concentration. In addition, PKA activity and tyrosine phosphorylation were also significantly altered. Thus, novaluron affects sperm viability, sperm motility, and motion kinematics during capacitation. Furthermore, it may promote the reduction in acrosome reactions. The physiological suppression of sperm function may depend on abnormal tyrosine phosphorylation via the alteration of PKA activity. Therefore, we suggest that it is necessary to consider reproductive toxicity when using novaluron as a pesticide.

Effects of novaluron ingestion and topical application on German cockroach (Blattella germanica) development and reproduction

BACKGROUND

Insect growth regulators disrupt insect development and reproduction. Chitin synthesis inhibitors (CSIs) allow the insect to grow normally, but because chitin is an essential component of the cuticle, formation of a new cuticle and ecdysis are prevented and the insect dies. CSIs can also kill embryos by disrupting their normal development. We evaluated the potential utility of novaluron in bait formulations against the German cockroach (Blattella germanica L.).

RESULTS

The minimum novaluron intake that interfered with molting and reproduction was assessed by exposing nymphs and adult females to novaluron. Results showed that 1 day of feeding on 0.1% novaluron was sufficient to disrupt molting in nymphs and prevent adult females from developing viable oothecae. The long-term effects on gravid females were investigated by feeding females 0.1% novaluron for different 5-day intervals during successive stages of gestation. Results demonstrated that gravid females fed novaluron during any period of gestation were able to produce viable eggs. To determine if ingestion of novaluron affected mating success and fertility of adult males, males were fed novaluron and then allowed to mate with untreated virgin females. Males that fed on novaluron successfully mated, and the females produced viable oothecae. Finally, direct comparisons revealed that novaluron is equally effective by ingestion and topical application.

CONCLUSIONS

Novaluron caused mortality in nymphs and interfered with ootheca production in adult females, but only before they formed an ootheca. It successfully reduced German cockroach populations in cages and has potential to be incorporated in cockroach baits.

Novaluron prevents oogenesis and oviposition by inducing ultrastructural changes in ovarian tissue of young adult Lygus lineolaris

BACKGROUND

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), has emerged as a major pest of cotton, Gossypium hirsutum L, in the mid-southern USA. In the early 1990s L. lineolaris populations developed resistance to several classes of conventional insecticides, increasing the need for insecticides with alternative modes of action such as insect growth regulators (IGRs) for integrated pest management (IPM). The benzoylphenyl urea (BPU) class of IGRs acts by disrupting the growth and development of immature stages of insects, but little is known about its impact on adult stages.

RESULTS

The effect of novaluron (Diamond™ 0.83EC), a BPU with known chitin synthesis inhibitor activity, was investigated on adult females of L. lineolaris. Treatment of 1-day-old adults with 600 ppm of novaluron in the diet prevented oviposition, while treatment of older females had no impact on oviposition. Oral novaluron exposure of adults of all ages reduced the viability of eggs laid. Novaluron treatment caused ultrastructural changes in the ovaries of 1-day-old adults (48 h post exposure), distorting the follicular epithelial cell architecture of developing oocytes. Additionally, novaluron treatment decreased the chitin content in ovarian tissue.

CONCLUSION

Our results suggest that chitin or chitin-like components in the developing ovaries of adult L. lineolaris are a target of IGRs such as novaluron, but its activity is specific to a critical time during development. This enhances our understanding of the effects of BPUs on adult insects and could lead to incorporation of IGRs in IPM for controlling adult insect pest populations in the field. © 2020 Society of Chemical Industry.

Ingestion of Novaluron Elicits Transovarial Activity in Stephanitis pyrioides (Hemiptera: Tingidae)

Azaleas (Rhododendron L. spp.) are widely grown ornamental plants in eastern and western regions of the USA. The azalea lace bug, Stephanitis pyrioides (Scott) (Hemiptera: Tingidae), is an important insect pest of azaleas. Adults and nymphs of S. pyrioides consume chlorophyll in azalea foliage, and severely affected plants appear bleached. Neonicotinoid insecticides are effective and widely used for S. pyrioides control; however, nursery growers and landscape professionals are concerned about nontarget effects on beneficial insects and demand neonicotinoid-free plants. There is clearly a need to develop reduced-risk control strategies for S. pyrioides. The insect growth regulator (IGR) novaluron elicits transovarial activity when adult S. pyrioides are exposed to it. However, it is not certain whether transovarial effects can be observed when S. pyrioides adults that colonize the abaxial leaf surface ingest novaluron residues deposited on the adaxial leaf surface. Experiments were conducted to assess transovarial activity upon exposure to various application rates of novaluron alone and novaluron with various adjuvants. The numbers of nymphs were significantly lower when the full rate of novaluron was applied on the adaxial surface of leaves compared to the number of nymphs on non-treated leaves. The densities of nymphs were not significantly different between the half and full rates of novaluron treatment. When novaluron with various adjuvants was applied to the adaxial surface of the leaves, the densities of nymphs were significantly lower under the novaluron treatments compared to the non-treated leaves, regardless of the type of adjuvant added. There was no significant difference between treatment with novaluron alone and the treatments of novaluron with adjuvants. These data show that transovarial activity was elicited in adults of S. pyrioides when novaluron was applied on the adaxial leaf surface.

Development-Disrupting Chitin Synthesis Inhibitor, Novaluron, Reprogramming the Chitin Degradation Mechanism of Red Palm Weevils

Disruption in chitin regulation by using chitin synthesis inhibitor (novaluron) was investigated to gain insights into the biological activity of chitinase in red palm weevils, an invasive pest of date palms in the Middle East. Impact of novaluron against ninth instar red palm weevil larvae was examined by dose-mortality response bioassays, nutritional indices, and expression patterns of chitinase genes characterized in this study. Laboratory bioassays revealed dose-dependent mortality response of ninth-instar red palm weevil larvae with LD₅₀ of 14.77 ppm of novaluron. Dietary growth analysis performed using different doses of novaluron (30, 25, 20, 15, 10, and 5 ppm) exhibited very high reduction in their indexes such as Efficacy of Conversion of Digested Food (82.38%) and Efficacy of Conversion of Ingested Food (74.27%), compared with control treatment. Transcriptomic analysis of red palm weevil larvae characterized numerous genes involved in chitin degradation including chitinase, chitinase-3-like protein 2, chitinase domain-containing protein 1, Endochitinase-like, chitinase 3, and chitin binding peritrophin-a domain. However, quantitative expression patterns of these genes in response to novaluron-fed larvae revealed tissue-specific time-dependent expression patterns. We recorded overexpression of all genes from mid-gut tissues. Growth retarding, chitin remodeling and larvicidal potential suggest novaluron as a promising alternate for Rhynchophorus ferrugineus management.

Transovarial effects of insect growth regulators on Stephanitis pyrioides (Hemiptera: Tingidae)

BACKGROUND

Azalea lace bug, Stephanitis pyrioides (Scott) (Hemiptera: Tingidae) is a serious insect pest of azaleas (Rhododendron L. spp.) in the USA. S. pyrioides feeding causes chlorosis, which affects the aesthetic value and marketability of azalea plants. Management of S. pyrioides primarily involves neonicotinoid insecticides and their use has been drastically reduced or discontinued. Insect growth regulators (IGRs) are known to elicit transovarial activity as IGR-exposed adults produce non-viable eggs, which is not documented for S. pyrioides. Thus, transovarial activity of novaluron, azadirachtin, pyriproxyfen and buprofezin has been explored against S. pyrioides.

RESULTS

A low number of S. pyrioides young instars was produced when adults were exposed to topical novaluron compared with non-treated adults. When adults contacted dried residues of novaluron and buprofezin, production of young instars was reduced relative to non-treated controls. When insects exposed to 1.0× and < 1.0× doses of novaluron were compared, the number of young instars produced was similar.

CONCLUSION

Transovarial activity was elicited in S. pyrioides when adults were exposed to IGRs, especially novaluron. When adults were exposed to < 1.0× (up to 0.25×) and 1.0× doses of novaluron, the transovarial effect was similar. © 2019 Society of Chemical Industry.

Influence of Insect Growth Regulators on Stephanitis pyrioides (Hemiptera: Tingidae) Eggs and Nymphs

The azalea lace bug, Stephanitis pyrioides (Scott) (Hemiptera: Tingidae), is an important insect pest of azaleas (Rhododendron L. spp.) in the USA. Stephanitis pyrioides feeds on azalea foliage and causes extensive chlorosis, which reduces the aesthetic value and marketability of these plants. Because the use of neonicotinoid insecticides has been dramatically reduced or discontinued, growers and landscape managers are seeking alternative tools or strategies to control this insect. Although insect growth regulators (IGRs) are known for their activity against immature insect stages, their activity against egg hatching has not been addressed thoroughly, specifically against S. pyrioides. Thus, a series of experiments was conducted to understand the ovicidal activity of IGRs using novaluron, azadirachtin, pyriproxyfen, and buprofezin against S. pyrioides. The number of newly emerged young instars was significantly lower when leaves implanted with eggs were sprayed on both sides with novaluron, azadirachtin, and buprofezin compared to nontreated and pyriproxyfen treatments. When IGRs plus adjuvant were applied to the adaxial surface of the leaves, the densities of the newly emerged nymphs were significantly lower under the novaluron treatment compared to the nontreated leaves. However, there was no significant difference in the number of nymphs that emerged in the absence of adjuvant. Furthermore, close monitoring revealed reduced levels of egg hatching in the presence of adjuvant with novaluron compared to its absence. The data show that the survival of S. pyrioides first instars was not affected by exposure to dried IGR residues.

Benzoylphenyl ureas as veterinary antiparasitics. An overview and outlook with emphasis on efficacy, usage and resistance

Six benzoylphenyl ureas are currently used in formulations approved as veterinary medicines: diflubenzuron for fly control mainly on cattle, lice and blowfly strike control on sheep, and lice control on farmed salmonids; lufenuron for flea control on dogs and cats and for lice control on farmed salmonids; triflumuron for lice and blowfly strike control on sheep; fluazuron for tick control on cattle; teflubenzuron for lice control on farmed salmon; and novaluron for fly and tick control on cattle and for flea control on dogs. Resistance to diflubenzuron and triflumuron has already been reported for sheep body lice and blowflies, and to fluazuron in cattle ticks. These and other minor veterinary usages, as well as the current status of resistance, are reviewed and perspectives for future opportunities are discussed based on unexplored potentials and threats posed by future resistance development.

Effects of Insect Growth Regulators on Bagrada hilaris (Hemiptera: Pentatomidae)

Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae) is a serious pest of cruciferous crops in the central coast of California. Management of B. hilaris primarily involves the use of broad spectrum insecticides, such as pyrethroids and neonicotinoids, when the pest invades a crop field. Insect growth regulators (IGRs) are known for their efficacy on nymphal stages of B. hilaris, but little is known about their transovarial effects. Thus, the major objective of this study was to determine the transovarial effects of IGRs such as novaluron, diflubenzuron, and azadirachtin, when adults are exposed to direct topical spraying and dried residues. In addition, a direct topical spray of IGRs on older instars (fourth and fifth instars) was examined at 1-, 3-, and 7-d post-treatment. The number of young instars (first and second instars) and adults was recorded up to ~31 d after exposure. In the topical spray assays, the number of young instars was significantly lower for novaluron, diflubenzuron, and azadirachtin than for the nontreated control. The number of young instars that emerged after novaluron treatment was low (0-11%). In the assays with dried residues, the number of young instars that developed was significantly lower for novaluron treatment than for the other IGRs and the nontreated control. There was no significant difference among diflubenzuron, azadirachtin, and nontreated control treatments in the development of young instars. In the assays with a topical spray of IGRs on older instars, significantly more nymphs died at 3 and 7 d after exposure. The IGRs had no clear impact on adults.

(Megachilidae)

BACKGROUND

The chitin synthesis inhibitor novaluron can suppress pests that affect alfalfa seed production, but can negatively affect reproductive success in the alfalfa pollinator Megachile rotundata. Novaluron is considered to be a reduced-risk insecticide because it disrupts ecdysis and is non-lethal to adult insects, but some exposed adults have fewer eggs and suppressed egg hatch. For this experiment, bees nested in field cages where they were exposed to alfalfa that had never been treated with novaluron, alfalfa that had recently been sprayed or alfalfa that had been sprayed 1 and 2 weeks earlier.

RESULTS

Compared with the control, greater proportions of dead eggs and larvae and lower proportions of live prepupae occurred when bees were exposed to recent novaluron sprays as well as one- or two-week old spray residues. Two possible routes of residual pesticide exposure were revealed. Mother bees become contaminated through ingestion or direct contact, or pollen-nectar provisions become contaminated with novaluron (1) on or within leaf pieces that surround provisions or (2) transferred from mother bees' bodies to provisions.

CONCLUSION

We found strong immature mortality effects of novaluron and its residues on M. rotundata. Understanding all possible pesticide exposure routes for pollinating bees enhances decision-making for maintaining bee populations while protecting crops. © 2016 Society of Chemical Industry.

Baseline Susceptibility of Lygus lineolaris (Hemiptera: Miridae) to Novaluron

Tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), populations were collected from field locations in the Mississippi River Delta of Arkansas, Louisiana, and Mississippi. Third-instar F(1) nymphs from each field location, in addition to a laboratory colony, were screened for susceptibility to novaluron. Both a glass vial bioassay and a diet-incorporated bioassay used dose-response regression lines to calculate LC(50) and LC(90) values for novaluron. Mean LC(50s) for glass vial bioassays ranged from 44.70 ± 3.58 to 66.54 ± 4.19 μg/vial, while mean LC(50s) for diet-incorporated bioassays ranged from 12.10 ± 0.77 to 17.63 ± 2.42 μg/200 ml of artificial diet. A comparison of LC(50) values from the same field population screened using both bioassay methods failed to show a relationship. LC(50) values from field locations were compared with a historically susceptible population from Crossett, AR. Results indicated that considerable variability in susceptibility to novaluron exists within field populations of tarnished plant bugs across the Delta, including some locations with lower LC(50) values than a historically susceptible population.

Transovarial Effect of Novaluron on Tribolium castaneum (Coleoptera: Tenebrionidae) After Termination of Direct Contact

The insect growth regulator novaluron (Rimon 10 EC, Makhteshim-Agan Ltd, Israel) is used against many field pests on corn, vegetables, orchards, forests, and cotton plantations. Previously, we studied various effects of novaluron on stored grain pests. Termination in Tribolium castaneum (Herbst) eggs hatching after treating adults with novaluron and following restoration after adult transfer to untreated media was observed. The objective of this study was to investigate the restoration of T. castaneum egg hatch following transfer of adults from treated media to untreated favorable and unfavorable media. The time needed for hatching restoration of 50% of eggs laid by adults transferred from novaluron (1 ppm) treated flour to untreated flour (RT50) was 2.7 d. RT50 for those transferred to untreated wheat grain was 4.1 d. RT90 in flour was 3.6 d, in grain--6.1 d. Varieties of RTs in grain and in flour with nonoverlapping confidence intervals indicate that RTs were significantly different. Delay of eggs hatching restoration for adults transferred from treated flour to unfavorable media (Petri dishes with limited amount of flour, lying of eggs not detected) was observed. RT50 in flour was 2.1 d and RT90--3.1 d, while RT50 in the unfavorable media was 3.4 d and RT90 6.5 d. Delayed effect of egg hatching restoration after adult transfer to unfavorable media provides evidence of the significant role of insect physiological state in novaluron excretion and (or) degradation by T. castaneum females.

Laboratory and Field Evaluations of Mosquiron® 0.12CRD, a New Formulation of Novaluron, Against Culex Mosquitoes

Laboratory and field evaluations were conducted to assess the activity and efficacy of Mosquiron® 0.12CRD, a new formulation containing 0.12% novaluron, against immature Culex mosquitoes. In laboratory bioassays, this formulation was highly active against Culex quinquefasciatus as indicated by low inhibition of emergence (IE) values (IE50 and IE90). When Mosquiron 0.12CRD was applied at 1 briquet per underground stormwater vault, counts of late instars showed a significant reduction on day 28 posttreatment. When the late instars and pupae collected from Mosquiron-treated water were brought back to the laboratory for posttreatment observation, emergence inhibition was >90% on day 7. When the late instars from a laboratory colony of Cx. quinquefasciatus were exposed to the Mosquiron-treated water, 99% and 95% emergence inhibition was noted on day 7 and day 14, respectively. When Mosquiron 0.12CRD was applied at 11 briquets per vault, significant reductions of larval populations were encountered on days 7 and 35 posttreatment for early instars, and on days 14, 21, and 35 posttreatment for late instars. Laboratory observation of late instars and pupae sampled from the treated vault water showed nearly complete emergence inhibition from day 7 to day 28 posttreatment. A similar trend was observed in laboratory-reared late instars of Cx. quinquefasciatus when exposed to the treated water. Preliminary evaluations indicated that Mosquiron 0.12CRD is a useful new tool to control Culex mosquitoes breeding in persistent sources.

Lethality of reduced-risk insecticides against plum curculio (Coleoptera: Curculionidae) in blueberries, with emphasis on their curative activity

BACKGROUND

Historically, management of plum curculio, Conotrachelus nenuphar (Herbst), in highbush blueberries has focused on post-bloom broad-spectrum insecticide applications targeting the adults. Here, the efficacy of different classes of insecticides against various stages of C. nenuphar was compared, and a prebloom treatment with the chitin synthesis inhibitor novaluron in combination with a post-bloom insecticide application was tested.

RESULTS

Novaluron decreased the number of oviposition scars and eggs on fruit and reduced larval emergence by >60% when applied prebloom. Post-bloom applications of the oxadiazine indoxacarb and the organophosphate phosmet, but not the neonicotinoid acetamiprid, showed significant adulticidal activity. The neonicotinoids acetamiprid and thiamethoxam and phosmet showed significant curative activity on C. nenuphar larvae when applied topically to infested fruit, whereas the pyrethroid fenpropathrin, indoxacarb and novaluron were weaker curative agents. Residue profiles showed that acetamiprid and phosmet residues had the highest levels while fenpropathrin and novaluron had the lowest levels of fruit penetration.

CONCLUSIONS

In blueberries, novaluron showed anti-ovipositional/ovicidal activity, indoxacarb and phosmet showed adulticidal activity, while the neonicotinoids and phosmet showed best curative (larvicidal) control on C. nenuphar. A prebloom novaluron application in combination with a post-bloom treatment with an adulticidal/larvicidal insecticide is recommended for optimal multi-life-stage management of C. nenuphar. © 2013 Society of Chemical Industry.