The aggregation pheromone of Diorhabda elongata, a biological control agent of saltcedar(Tamarix spp.): identification of two behaviorally active components

Abstract

The leaf beetle Diorhabda elongata Brullé (Coleoptera: Chrysomelidae) has been introduced as a biological control agent for saltcedars, Tamarix spp., an exotic, invasive weedy tree in the western United State. Gas chromatographic (GC) analysis of volatiles collected from feeding male or female beetles, or saltcedar foliage alone, showed two components produced almost exclusively by males. These compounds elicited responses from antennae of male and female beetles in GC-electroantennographic detection (EAD) analyses. The compounds were identified as (2E,4Z)-2,4-heptadienal (1) and (2E,4Z)-2,4-heptadien-1-ol (2) by GC-mass spectrometry (MS), and confirmed with authentic standards. The two compounds were also detected at trace levels from feeding females and foliage controls, but the amounts from feeding males were 8-40 times higher, typically 55-125 ng per day per male. The amounts of 1 and 2 in collections from females did not differ significantly from amounts collected from control foliage. In field trials, 2 as a single component was as attractive as a 1:1 blend of 1 and 2. Compound 1 as a single component was more attractive than controls, but much less attractive than 2 or the blend. Males and females were attracted in about equal numbers, indicating that this is an aggregation pheromone.

Open field host selection and behavior by tamarisk beetles (Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars (Tamarix spp.) and risks to non-target athel (T. aphylla) and native Frankenia spp.

“…Adult densities peaked after an additional 4 weeks, indicating that a new adult generation emerged from larvae reared in bags, and these adults produced more egg masses and larvae on the saltcedar trees on which they were released than on athel, while not showing a preference for nearby unbagged saltcedar trees over athel. Aggregation pheromone releases by parental beetles (Cossé et al, 2005) could have influenced host selection by the new generation. The low overall beetle densities (0-1 beetle per m green length) and declines after 6 weeks were indicative of establishment failure at Kingsville, possibly caused by the somewhat lower suitability of T. canariensis/T.…”

Distribution of the subtropical tamarisk beetle,Diorhabda sublineata(Lucas, 1849) (Coleoptera: Chrysomelidae), in Mexico

“…Small differences in appearance and behavior in our cultures and tests at Temple, TX and Albany, CA led to detailed morphological examinations by James Tracy at Temple, that indicated 5 separate species (originally described as species or subspecies but later synonymized under D. elongata) (Tracy and Robbins, 2009). This was supported by DNA analyses by David Kazmer (ARS, Sidney, MT), cross mating experiments by David Thompson (NM State University, Las Cruces), Crete/Tunisian pheromone comparisons (Cossé et al 2005, ARS, Peoria, IL), and daylength/diapause characteristics (Bean et al, 2007a,b). Four of these 5 species have been released in the U.…”

“…The adults also congregate into mating swarms, regulated by a male aggregation pheromone (Cossé et al, 2005), which then disperse as somewhat intact swarms up to several miles distant in search of a healthy, undefoliated saltcedar food supply where they establish satellite colonies, as observed at Beals Creek, TX. This swarming behavior also serves as an effective predator avoidance strategy which allows the beetles to rapidly invade new areas before predator populations can respond, and to do this repeatedly.…”

“…Predation of eggs, larvae and adults in the trees by ladybird beetles, assassin bugs and spiders also may be high in some areas. The adults congregate in swarms (probably for mating) which migrate when populations are high and food is scarce and also may overwinter en masse under litter (Mityaev and Jashenko, 2007), both regulated by a male aggregation pheromone (Cossé et al 2005); this behavior may be a strategy for avoiding predators. The survival and rate of population increase in the field is that of a strong "r strategist", with a high reproductive rate but with high mortality from generalist arthropod and other predators and from host specific parasites in their homeland (but probably not in North America).…”

Salt cedar areawide pest management in the western USA.

“…Additionally, timed adult beetle counts were used to follow low-level beetle populations and, later, a beetle pheromone and a salt cedar extract were formulated (Cosse et al, 2005) that were very attractive to D. elongata beetles from China and Kazakhstan over distances of 10-20 m. These baits were incorporated into a trapping system and have been effectively used in monitoring the dispersal of the beetles at Lovelock, NY and other locations.…”