A novel approach to biocontrol: Release of live insect hosts pre-infected with entomopathogenic nematodes

Potential of entomopathogenic nematode-infected insect cadavers for the biocontrol of the red imported fire ant Solenopsis invicta

BACKGROUND

Entomopathogenic nematodes (EPNs) in an aqueous suspension treatment showed potential in the biocontrol of the red imported fire ant Solenopsis invicta, whereas colony relocation following this inundative application had restricted overall effectiveness. As a novel strategy, EPN pre-infected insect cadavers carrying the next generation of nematode-infective juveniles (IJs) might be used to efficiently manage insect pests. However, this strategy has not been tested on S. invicta. This study evaluated EPNs emerging from wax moth Galleria mellonella cadavers to facilitate infection of S. invicta compared to those used in aqueous suspensions.

RESULTS

Among seven EPN species, Steinernema riobrave and Heterorhabditis bacteriophora had the highest insecticidal efficiency in aqueous treatment. Cadavers of G. mellonella colonized by either one of two EPN species were not damaged by worker ants, ensuring that the IJs could develop within and emerge successfully from the cadavers. Likewise, compared to an aqueous suspension treatment with an equivalent number of IJs, treatment with an S. riobrave-infected cadaver increased the mortality of S. invicta by ≈10%, whereas infection by H. bacteriophora did not differ between treatments. However, the coexistence of S. riobrave- and H. bacteriophora-infected cadavers adversely affected the control of S. invicta, likely as a result of competition resulting from the increased dispersal of each emerging EPN species.

CONCLUSION

Using EPN-infected G. mellonella cadavers as a strategy increased the mortality of S. invicta in the laboratory. This study provides positive evidence for the future applications of S. riobrave-infected cadavers in the biocontrol of red imported fire ants. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Steinernema diaprepesi Nguyen & Duncan (Rhabditida: Steinernematidae), a new entomopathogenic nematode from Brazil

Entomopathogenic nematodes (EPNs) can control pests due to their mutual association with bacteria. The use of these biological control agents is increasing worldwide due to advances in research about its control efficiency, range of action and mass production. The identification of EPNs adapted to specific environmental and climatic conditions is important for sustainable pest suppression in integrated management (IPM) programs. The objective is to report, for the first time, the occurrence of the Steinernema diaprepesi in Brazil. Steel mesh traps with Galleria mellonella Linnaeus (Lepidoptera: Pyralidae) larvae were buried in red latosol cultivated with Eucalyptus. Infective juveniles (IJs) were isolated from dead larvae and multiplied in healthy ones of this host to confirm its pathogenicity and to start a laboratory population from the strain found in the field. The DNA of the IJs was extracted and amplified using PCR technique with the universal primers D2A and D3B. The detection of S. diaprepesi is the first report of this nematode in Brazil, increasing the knowledge about its distribution in the world and the diversity of EPNs that must be considered as agents of biological pest control in the country.

First record of a mermithid worm (Nematoda, Mermithidae) parasitizing a third instar nymph of Triatoma sordida (Stål, 1859) (Hemiptera, Reduviidae, Triatominae) from Mato Grosso, Brazil

A juvenile specimen of a mermithid (Nematoda) was found parasitizing a third instar nymph of Triatomasordida from Mato Grosso, Brazil. This is the first record of mermithid parasitism in a triatomine species. The Mermithidae represents a family of nematodes that are specialized insect parasites. Entomonematodes are one of the highly influential agents regulating the population dynamics of insects. This report introduces the opportunity to think about mermithids as a possible candidate for use as triatomine biological control.

Environmental tolerance of entomopathogenic nematodes differs among nematodes arising from host cadavers versus aqueous suspension

Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous suspension. In the heat tolerance bioassays, following exposure to 30 °C, 35 °C and 37. 5 °C, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 °C regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 °C to -2 °C. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.

Transmission Success of Entomopathogenic Nematodes Used in Pest Control

Entomopathogenic nematodes from the two genera Steinernema and Heterorhabditis are widely used as biological agents against various insect pests and represent a promising alternative to replace pesticides. Efficacy and biocontrol success can be enhanced through improved understanding of their biology and ecology. Many endogenous and environmental factors influence the survival of nematodes following application, as well as their transmission success to the target species. The aim of this paper is to give an overview of the major topics currently considered to affect transmission success of these biological control agents, including interactions with insects, plants and other members of the soil biota including conspecifics.

Targeting a Hidden Enemy: Pyriproxyfen Autodissemination Strategy for the Control of the Container Mosquito Aedes albopictus in Cryptic Habitats

Background

The Asian tiger mosquito, Aedes albopictus, is a vector of dengue, Chikungunya, and Zika viruses. This mosquito inhabits a wide range of artificial water-holding containers in urban and suburban areas making it difficult to control. We tested the hypothesis that female-driven autodissemination of an insect growth regulator could penetrate cryptic oviposition habitats difficult to treat with conventional insecticidal sprays.

Methodology

Oviposition preferences of Ae. albopictus females for open and cryptic cups were tested in semi-field experiments. Two conventional larvicidal sprayers were tested to determine droplet penetration and larvicidal efficacy in open and cryptic habitats using Bacillus thuringiensis var. israelensis (Bti) in the field. Finally, the efficacy of pyriproxyfen autodissemination stations was assessed in cryptic and open cups in residential areas during 2013 and 2014.

Principal Findings

Gravid females strongly preferred cryptic (53.1±12.9 eggs/cup) over open (10.3±4.3 eggs/cup) cups for oviposition. Cryptic cups showed limited droplet penetration and produced 0.1–0.3% larval mortality with a conventional backpack and low-volume sprays of Bti. The autodissemination stations effectively contaminated these cryptic cups (59.3–84.6%) and produced 29.7–40.8% pupal mortality during 2013–2014. Significant pupal mortality was also observed in open cups.

Conclusions

The autodissemination station effectively exploits the oviposition behavior of wild gravid females to deliver pyriproxyfen to targeted oviposition habitats. Although the pupal mortality in cryptic cups was relatively lower than expected for the effective vector control. Autodissemination approach may be a suitable supporting tool to manage Ae. albopictus immatures in the cryptic habitats those are less accessible to conventional larvicidal sprays.

Aedes albopictus is a highly invasive mosquito species and a competent vector of dengue, Chikungunya, Zika and other arboviruses. In the absence of therapeutics, vector control is the only means of controlling these diseases. Larvicides are important tool to limit mosquito populations. Backpack and low volume sprayers are heavily used for ground-based larvicide applications, but their potential to reach hidden or cryptic larval habitats is not well established. In the present study, we found that Ae. albopictus shows a strong oviposition preference for cryptic cups. Moreover, cryptic cups received limited droplet penetration using conventional spray methodologies, resulting in almost negligible larval mortality as compared to open cups in field experiments. We further evaluated the efficacy of an autodissemination station to deliver the insect growth regulator pyriproxyfen to cryptic cups in field experiments. Autodissemination shows good efficacy in transferring toxic concentrations of pyriproxyfen to cryptic cups and may provide a significant advantage over sprayers in delivering insecticide to the cryptic larval habitats strongly preferred by Ae. albopictus.

Nematodes (Mermithidae) parasitizing grasshoppers (Orthoptera: Acrididae) in the Pampean region, Argentina

This work provides the results of a survey of entomonematodes parasites of grasshoppers in grasslands of the Pampean Region, Argentina. Nymphs of Staurorhectus longicornis Giglio-Tos, Laplatacris dispar Rhen, 1939, Dichroplus elongatus Giglio-Tos, 1894 and Metaleptea brevicornis (L.) (Orthoptera: Acrididae) were collected. Mermithidae was the only family registered with seven species: Agamermis decaudata Cobb, Steiner and Christie, 1923, Amphimermis bonaerensis Miralles and Camino, 1983, Amphimermis dichroplusi Camino and Lange, 1997, Amphimermis ronderosi Camino and Lange, 1997, Hexamermis coclhearius Stock and Camino, 1992, Hexamermis ovistriata Stock and Camino, 1992, and Longimermis acridophila Camino and Stock, 1989. The values of parasitism ranged between 1-12%, and intensity not overcome the number of 5.0 nematodes per larva. The nematodes observed showed specificity, not registering the same species of parasite in more than one host species. The Pampean region constituted an area with high diversity of mermithids where new species could be consider as bioregulator agents of this troublesome insect pests in agricultural areas of Argentina.