Journal of Nematology (2003) 35, 187-193

L.W. Duncan, D.C. Dunn, G. Bague and K. Nguyen (2003)
Competition between entomopathogenic and free-living bactivorous nematodes in larvae of the weevil Diaprepes abbreviatus
Journal of Nematology 35 (2), 187-193
Abstract: Field and laboratory experiments were conducted to determine the degree to which free-living, bactivorous nematodes (FLBN) are able to competitively displace entomopathogenic nematodes (EPN) from insect cadavers. Two hundred larvae of the insect Diaprepes abbreviatus were buried at regular intervals during 2 years in experimental plots that were untreated or treated twice annually with Steinernema riobrave. Larvae were recovered after 7 days, and nematodes emerging from cadavers during the next 30 days were identified. The monthly prevalence of FLBN was directly related to that of S. riobrave (r = 0.38; P = 0.001) but was not related to the prevalence of the endemic EPN, S. diaprepesi, Heterorhabditis zealandica, H. indica, or H. bacteriophora (r= 0.02; P= 0.80). In a second experiment, treatment of small field plots with S. riobrave increased the prevalence of insect cadavers in which only FLBN were detected compared to untreated controls (30% vs. 14%; P= 0.052), and increased numbers of FLBN per buried insect by more than 10-fold. In the laboratory, sand microcosms containing one D. abbreviatus larva were treated with (i) the FLBN, Pellioditis sp.; (ii) S. riobrave; (iii) S. riobrave + Pellioditis; or (iv) neither nematode. Insect mortality was higher in the presence of both nematodes (57%) than when S. riobrave was alone (42%) (P= 0.01). An average of 59.2 Pellioditis sp. g^-1 insect body weight emerged in the presence of S. riobrave, whereas 6.2 nematodes g^-1 insect were recovered in the absence of the EPN (P= 0.01). Pellioditis sp. reduced the number of S. riobrave per cadaver, by 84%; (P= 0.03), and per available insect by 82% (P= 0.001), compared to S. riobrave alone. Population size of S. diaprepesi was not affected by Pellioditis sp. in experiments of the same design. Faster development (P= 0.05) and nutrient appropriation within the insect cadaver by S. diaprepesi compared to S. riobrave may increase the fitness of the former species to compete with Pellioditis sp. The results of these studies demonstrate the potential of FLBN to regulate population densities of EPN and to dampen estimates of EPN-induced mortality of insect pests in the field.
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Database assignments for author(s): Larry W. Duncan

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
environment/habitat manipulation

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Diaprepes abbreviatus	Citrus (genus)	U.S.A. (SE)
Steinernema riobrave/Xenorhabdus cabanillasii (entomopathogen)	Diaprepes abbreviatus	Citrus (genus)	U.S.A. (SE)
Steinernema diaprepesi (entomopathogen)	Diaprepes abbreviatus	Citrus (genus)	U.S.A. (SE)