ABSTRACT

In Fiji, little or no attention has been given to entomopathogenic nematodes (EPNs) in biocontrol programs due to the lack of awareness about their occurrence and distribution in Fiji. A survey of EPNs was conducted for the first time in Fiji Islands in 2012 and 2013, throughout the eight provinces in Viti Levu to determine the occurrence and distribution across different habitat in Viti Levu. The soil samples from various habitats were collected and assayed for the presence of EPN using Galleria mellonella as baits. EPNs were recovered from five out of seven provinces with 35 positive sites (7.3%) out of 478 sites sampled. The only EPN genera encountered was Heterorhabditis. Steinernema was not isolated from any of the samples. Characterization of isolates was done by using morphometric and molecular examinations and isolates were identified as Heterorhabditis indica. H. indica isolates were primarily recovered from leeward side of the Viti Levu Island along the coastline and riversides, being more prevalent in lighter soil with pH > 6. Further, this study found significant association between habitat type, soil type, soil pH, average annual rainfall and EPN occurrence. This is the first record of naturally occurring EPNs in Fiji. The found nematodes will serve as the basis for efficacy screening with the ultimate aim of delivering effective, more sustainable and environmentally safe control for agricultural pests in Fiji.

Weeds can act as reservoir hosts of a range of pests and diseases. Information and knowledge on the host status of weeds to common pests and diseases can be used to develop integrated weed and pest management strategies. As part of a survey on the distribution and diversity of root-knot nematodes on crops in Fiji, the root-knot nematode host status of weeds was also studied. Weeds growing in root-knot nematode infested farms (n= 189) and bioassay pot soil samples (n= 277) were identified, and their host status was determined on the basis of a root gall and egg-mass index scale from 0 to 5. A total of 45 weed species were recorded as potential weed hosts of root-knot nematodes with a gall index from 1 to 5. Using the weed and tomato bioassay method, a total of 11 nonhost weed species were recorded with a gall index of 0, relative to infected tomato growing in pot soil samples. Common weeds infected by root-knot nematodes on farms and in bioassay pot soil included slender amaranth, old world diamond-flower, tropic ageratum, sicklepod, mimbra, balsamapple, purple bushbean, little ironweed, ivy gourd, and cutleaf groundcherry. The presence of egg masses on the weed hosts indicated their ability to sustain root-knot nematode populations and, thus, their potential to act as reservoir hosts.

Fiji’s swallowtail butterfly, Papilio schmeltzi, is a Rutaceae feeding, tropical Papilionid butterfly that is endemic to the Fiji islands and generally occurs in low density. Field observations on habitat and the seasonal activity patterns of P. schmeltzi were carried out in the Vatukarasa area in Korolevu, Sigatoka over the course of one year. P. schmeltzi adults were found throughout the year but with dry and wet seasonal variation in abundance. High abundance was recorded for all the P. schmeltzi stages during the dry season (May to September). Adults and larvae were the most abundant when compared to eggs and pupae, and showed the greatest variation with respect to distribution of life stages throughout the year. P. schmeltzi currently occurs at four localities on the mainland and ten localities in the outer islands, with high abundance in Sigatoka and Koro Island. Adults of the species mainly occupy isolated forest edge habitat and gardens near forested areas and display a strong affinity for running water. At least two larval host plants, Micromelum minutum and Citrus reticulata, were found to sustain populations of P. schmeltzi, in its natural environment.

Entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are obligate parasites of soil inhibiting insects. EPNs are being widely researched as promising biocontrol agents for a wide range of agricultural pests. It is known that strains of EPNs isolated from different geographical regions differ in their attributes, such as host-finding ability, host range, infectivity, reproduction, and environmental stress tolerance. A precise knowledge of these factors is therefore an essential pre-requisite for devising successful strategies to use these nematodes in biological control programmes. Thus, ecological characterisation of the EPN Heterorhabditis indica (Rhabditida: Heterorhabditidae) newly isolated and representing the only species of EPN reported from the island of Viti Levu, Fiji was carried out using Galleria mellonella larvae (L) (Pyralidae: Galleriinae) as hosts to allow comparisons between bioassays conducted in different laboratories around the world. Temperature data showed that native isolates of H. indica are warm-adapted nematodes with thermal range for infectivity between 15˚C and 35˚C and can reproduce between 20˚C and 30˚C. They are highly virulent with LC50 values against G. mellonella ranging from 2.8 IJ to 3.8 IJ/larva. However, they showed poor desiccation tolerance and fail to infect hosts in soil with moisture levels below 8%. They showed a moderate level of hypoxic tolerance and can be stored at 15˚C for 4 months. Results also showed great variability within the selected native isolates of H. indica. Beneficial traits for selected isolates were added up to identify a superior candidate. The current study also suggested that the thermal niche breadth for infection can differ among conspecific strains of an EPN species. The results of this experimental study on ecological aspects of these native isolates of H. indica should form a basis for their potential use in biological control of insect pests in Fiji.

No abstract

Root-knot nematodes, Meloidogyne spp., are the major nematode pests of economic crops worldwide. Use of conventional nematicides has been one of the most effective methods to reduce their populations. However, the ban on many effective nematicides in recent past has necessitated the search for alternative sources of effective and ecofriendly chemicals for nematode control. The nematicidal potential of fifteen Leguminosae seeds (wild and cultivated) was assessed, in vitro, against juveniles of Meloidogyne incognita (Kofoid & White) Chitwood. Each standard aqueous seed extract, 25g/100ml (w/v), was evaluated at dilutions, 1:10, 1:20, and 1:40 at 27+1�C for 24 hours. The majority of seed extracts caused high mortality rates, especially in 1:10 concentration. Trigonella foenum graceum, Sesbania sesban, Albizzia lebbak, Cassia fistula and Pongamia glabra were the most efficacious (above 90% mortality). S. sesban and P. glabra were significantly effective even in the lowest concentration (1:40).

Entomopathogenic nematode (EPN) Heterorhabditis indica is a promising biocontrol candidate. Despite the acknowledged importance of EPN in pest control, no extensive data sets or maps have been developed on their distribution at global level. This study is the first attempt to generate Ecological Niche Models (ENM) for H . indica and its global Habitat Suitability Map (HSM) for H. indica to generate biogeographical information and predicts its global geographical range and help identify of prospective areas for its exploration and to help identify the suitable release areas for biocontrol purpose. The aim of the modeling exercise was to access the influence of temperature and soil moisture on the biogeographical patterns of H . indica at the global level. Global Heterorhabditis indica ecosystems. CLIMEX software was used to model the distribution of H . indica and assess the influence of environmental variable on its global distribution. In total, 162 records of H . indica occurrence from 27 countries over 25 years were combined to generate the known distribution data. The model was further fine‐tuned using the direct experimental observations of the H . indica's growth response to temperature and soil moisture. Model predicts that much of the tropics and subtropics have suitable climatic conditions for H . indica . It further predicts that H . indica distribution can extend into warmer temperate climates. Examination of the model output, predictions maps at a global level indicate that H . indica distribution may be limited by cold stress, heat stress, and dry stresses in different areas. However, cold stress appears to be the major limiting factor. This study highlighted an efficient way to construct HSM for EPN potentially useful in the search/release of target species in new locations. The study showed that H . indica which is known as warm adapted EPN generally found in tropics and subtropics can potentially establish itself in warmer temperate climates as well. The model can also be used to decide the release timing of EPN by adjusting with season for maximum growth. The model developed in this study clearly identified the value and potential of Habitat Suitability Map (HSM) in planning of future surveys and application of H . indica .