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United States Department of Agriculture

Agricultural Research Service


Location: Imported Fire Ant and Household Insects

Title: Fire ant baits and biocontrol with pathogens update

item Oi, David

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 17, 2010
Publication Date: N/A

Technical Abstract: The insect growth regulator (IGR) methoprene (isopropyl-(2E,4E,7R,S)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate) has been shown to have deleterious effects on red imported fire ants, Solenopsis invicta. It interferes with normal development of worker caste brood and reduces queen egg production (Vinson and Robeau 1974). Methoprene is a racemic mixture of two enantiomers (R and S in a ratio of 1:1) with the juvenile hormone activity restricted to the S enantiomer (Henrick et al. 1978, World Health Organization 2002). The S enantiomer is the active ingredient in some commercially available fire ant baits. The efficacy of fire ant bait containing only the S enantiomer (0.5% (S)-methoprene) was compared to baits comprised of a racemic mixture (0.5% R and S enantiomers in a 1:1 ratio) and a standard IGR bait containing pyriproxyfen (0.5%). Efficacy was based on worker brood reduction in laboratory colonies of S. invicta containing approximately 21,000 workers, 20 ml brood, and 1 queen for 6 replicates per treatment. There were no significant differences between the S and RS methoprene baits with over 88% brood reduction by the 5th week after bait access. Colonies accessing the pyriproxyfen bait had faster brood reductions; 74% at 3 weeks and 97% at 5 weeks. Colonies fed control bait of 30% soybean oil on corn grit grew in size until the 5th week when there was 17% reduction. Symptoms of a virus infection, possibly Solenopsis invicta virus 3 (Valles and Hashimoto 2009), was evident at week 6 with control colonies exhibiting about 70% brood reduction. Note that this laboratory study optimized bait efficacy by providing unrestricted access to bait after colonies were starved, and may not reflect differences in field efficacy or in bait formulation. Fire ant decapitating phorid flies can acquire the fire ant pathogen Kneallhazia solenopsae when they develop in infected S. invicta (Oi et al. 2009). To determine the prevalence of K. solenopsae in field-collected phorid flies, Pseudacteon curvatus females were collected at four sites having 0 to 64% of the S. invicta nests infected with K. solenopsae. Based on PCR detections in individual flies, infection prevalence averaged 11.5% (range, 4.8-15.6%). K. solenopsae infection prevalence in flies was independent of K. solenopsae infection in S. invicta nests at the collection sites (Valles et al. 2009). Preliminary studies also were conducted to determine if infected phorid flies can vector K. solenopsae. Infected phorid flies were confined with small S. invicta colonies which allowed flies to oviposit on worker ants, or to be eaten by the ants. Thus far, there has been no evidence of transmission. The host range of K. solenopsae was previously thought to be restricted to fire ants in the Solenopsis saevissima species group. An unpublished report by Snowden and Vinson (2006) indicated natural infections occur in the tropical fire ant, Solenopsis geminata, in contrast to laboratory inoculations and field surveys of S. geminata in Florida (Oi and Valles 2009). Further examinations of samples from Mexico and Texas have detected K. solenopsae in S. geminata. However, preliminary phylogenetic analyses indicated possible variations in K. solenopsae from different hosts.

Last Modified: 1/29/2015
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