Coconut Rhinoceros Beetle in Samoa: Review of a Century-Old Invasion and Prospects for Control in a Changing Future.

It is now more than 100 years since the coconut rhinoceros beetle (CRB: Oryctes rhinoceros L.) was first detected in the Pacific Island state of Samoa. The exotic pest from Asia became the principal pest of coconut palms in Samoa and, from this first point of invasion, spread to several surrounding countries in the South-West Pacific Ocean. An intensive control operation was initiated, but the beetle could not be eliminated. Various pest management strategies were attempted but had limited success until the introduction of a biological control agent (BCA), Oryctes rhinoceros nudivirus (OrNV), during the late 1960s and early 1970s. The biocontrol release was very successful and became the prime example of "classical biological control" of an insect pest by a virus. Changing economic and social conditions in Samoa and other islands of the Pacific require a re-evaluation of the threat of CRB to coconut production to suggest how the IPM system may be modified to meet future needs. Therefore, it is timely to review the history of CRB in Samoa and summarize experiences in development of an integrated pest management (IPM) system limiting the impact of the pest. We also present results from a recent study conducted in 2020 on the island of Upolu to define the current status of the CRB population and its BCA, OrNV. The lessons from Samoa, with its long history of containment and management of CRB, are applicable to more recent invasion sites. Recommendations are provided to modify the IPM programme to enhance the sustainable control of CRB and support the ongoing coconut replantation program promoted by the Samoan government.

Development of a Yersinia entomophaga bait for control of larvae of the porina moth (Wiseana spp.), a pest of New Zealand improved grassland systems.

BACKGROUND: Porina is the common name for moths and larvae of the genus Wiseana (Lepidoptera: Hepialidae), some of which are significant pasture pests in New Zealand. Because of environmental concerns and the non-target effects of insecticide control measures, biological alternatives for the control of insect pests such as porina are required. RESULTS: Using a food preference assay and time-lapse photography, a range of low-cost food ingredients were assessed for their palatability to porina larvae. Lead candidates were combined into extruded bait variants, allowing assessment of their palatability to porina larvae. A composite bait consisting of palatable ingredients was developed, into which the porina-active entomopathogen Yersinia entomophaga was incorporated. A 7 day minimum median lethal dose of approximately 6.0 × ±1 × 106 Y. entomophaga cells per 0.02 g of bait was defined. Field trials showed that the mean change in larval density over time differed between treatments, with Y. entomophaga bait applied at 87 kg ha-1 resulting in a mean 65% reduction in larval density relative to the control plots, and diflubenzuron treatment resulting in a mean 77% reduction relative to the control plots. The mean dry matter yields over the course of the trial were highest for diflubenzuron (5029 kg ha-1 ), followed by the Y. entomophaga (4783 kg ha-1 ) and control (4673 kg ha-1 ) treatments. CONCLUSIONS: The bacterium Y. entomophaga applied as a composite bait offers an environmentally sustainable approach for porina pest control. © 2019 Society of Chemical Industry.

Genetic variation within species and haplotypes of the Wiseana (Lepidoptera: Hepialidae) complex and development of non-sequenced based identification tools to aid field studies.

BACKGROUND: Porina is the common name used to describe moths and caterpillars of the seven endemic species and three haplotypes of Wiseana in New Zealand. Several species have adapted to eating introduced pasture plants; however, a paucity of defining morphological characteristics has meant that porina are grouped as indistinguishable species within a complex. This study aimed to develop non-sequencing identification methods for porina species. RESULTS: We sequenced 1718 bp of the mitochondrial cytochrome oxidase genes for all Wiseana species and haplotypes using 75 specimens collected from 42 sites throughout New Zealand. Two identification methods were developed; the high-resolution melt method uses 106 bp of the cytochrome oxidase I gene, and the restriction fragment polymorphism method uses a larger 700 bp region from the same gene. Validation was performed on a further 275 specimens. Melt curve profiles varied more with population heterogeneity than digest results. In both methods, W. mimica and W. jocosa were inseparable. W. fuliginea grouped with W. mimica and W. jocosa in the restriction method, but the melt curve profile differed. CONCLUSION: Until now, ecological studies of porina at the species level have been implausible. Our non-sequencing based methods allow rapid identification of moths and caterpillars to species and haplotype level, paving the way for ecological studies of pasture pest species and the development of species-specific mitigation strategies. © 2017 Society of Chemical Industry.

Endosymbiotic candidates for parasitoid defense in exotic and native New Zealand weevils.

Some insects are infected with maternally inherited bacterial endosymbionts that protect them against pathogens or parasitoids. The weevil Sitona obsoletus (=Sitona lepidus) is invasive in New Zealand, and suspected to contain such defensive symbionts, because it is particularly resistant to a Moroccan strain of the parasitoid Microctonus aethiopoides (which successfully attacks many other weevil species), and shows geographic variation in susceptibility to an Irish strain of the same parasitoid. Using 454 pyrosequencing, we investigated the bacterial community associated with S. obsoletus, two other exotic weevils (Sitona discoideus and Listronotus bonariensis) and two endemic New Zealand weevils (Irenimus aequalis and Steriphus variabilis). We found that S. obsoletus was infected by one strain of Wolbachia and two strains of Rickettsia, none of which were found in any other weevil species examined. Using diagnostic PCR, we found that S. obsoletus in the Northland region, where parasitism is highly variable, were primarily infected with Wolbachia and Rickettsia strain 2, indicating that these two symbionts should be investigated for potential defensive properties. In comparison, S. discoideus lacked any apparent maternally inherited bacterial endosymbionts. In the other weevil species, we found a different strain of Wolbachia and two different strains of Spiroplasma. Two weevil species (St. variabilis and L. bonariensis) were infected with distinct strains of Nardonella, the ancestral endosymbiont of weevils, whereas three weevil species (S. obsoletus, S. discoideus, and I. aequalis) lacked evidence for Nardonella infection. However, I. aequalis was consistently infected with a novel Enterobacteriaceae strain, suggesting that a symbiont replacement may have taken place, similar to that described for other weevil clades.

Development and validation of a quick easily used biochemical assay for evaluating the viability of small immobile arthropods.

Quickly, accurately, and easily assessing the efficacy of treatments to control sessile arthropods (e.g., scale insects) and stationary immature life stages (e.g., eggs and pupae) is problematic because it is difficult to tell whether treated organisms are alive or dead. Current approaches usually involve either maintaining organisms in the laboratory to observe them for development, gauging their response to physical stimulation, or assessing morphological characters such as turgidity and color. These can be slow, technically difficult, or subjective, and the validity of methods other than laboratory rearing has seldom been tested. Here, we describe development and validation of a quick easily used biochemical colorimetric assay for measuring the viability of arthropods that is sufficiently sensitive to test even very small organisms such as white fly eggs. The assay was adapted from a technique for staining the enzyme hexokinase to signal the presence of adenosine triphosphate in viable specimens by reducing a tetrazolium salt to formazan. Basic laboratory facilities and skills are required for production of the stain, but no specialist equipment, expertise, or facilities are needed for its use.