Potential of "lure and kill" in long-term pest management and eradication of invasive species.

"Lure and kill" technology has been used for several decades in pest management and eradication of invasive species. In lure and kill, the insect pest attracted by a semiochemical lure is not "entrapped" at the source of the attractant as in mass trapping, but instead the insect is subjected to a killing agent, which eliminates affected individuals from the population after a short period. In past decades, a growing scientific literature has been published on this concept. This article provides the first review on the potential of lure and kill in long-term pest management and eradication of invasive species. We present a summary of lure and kill, either when used as a stand-alone control method or in combination with other methods. We discuss its efficacy in comparison with other control methods. Several case studies in which lure and kill has been used with the aims of long-term pest management (e.g., pink bollworm, Egyptian cotton leafworm, codling moth, apple maggot, biting flies, and bark beetles) or the eradication of invasive species (e.g., tephritid fruit flies and boll weevils) are provided. Subsequently, we identify essential knowledge required for successful lure and kill programs that include lure competitiveness with natural odor source; lure density; lure formulation and release rate; pest population density and risk of immigration; and biology and ecology of the target species. The risks associated with lure and kill, especially when used in the eradication programs, are highlighted. We comment on the cost-effectiveness of this technology and its strengths and weaknesses, and list key reasons for success and failure. We conclude that lure and kill can be highly effective in controlling small, low-density, isolated populations, and thus it has the potential to add value to long-term pest management. In the eradication of invasive species, lure and kill offers a major advantage in effectiveness by its being inverse density dependent and it provides some improvements in efficacy over related control methods. However, the inclusion of insecticides or sterilants in lure and kill formulations presents a major obstacle to public acceptance.

Can ménage-a-trois be used for controlling insects?

We propose a new cross-species disruption approach that might be capable of interrupting mating of one species that uses another insect species as the mercenary agent. We argue that insects treated with a sufficiently powerful attractant for a second species might interfere with mating of one or both species, for example, by leading males astray in pursuit of the false trails created by suitably dosing individuals of the first species. Our reciprocal test systems used (1) methyl eugenol, an attractant for male oriental fruit flies (Bactrocera dorsalis), applied to melon flies (B. cucurbitae) and (2) cuelure, a lure for male melon flies, applied to B. dorsalis. There was no mortality 1 week after either attractant was applied to individual flies at doses up to 100 ng, which was effective in attracting insects in a field cage and in the field. In wind tunnel choice tests, 100 ng of either lure topically applied to tethered flies attracted fruit fly males of the second species, which exhibited prolonged bouts of physically disruptive behaviors including chasing and bumping. In small cages, treatment of males did not reduce mating of either species, with one group of three (ménage) per cage. However, in large field cages with multiple pairs of both species present, there was a significant reduction in the mating of melon flies resulting from methyl eugenol applied to males compared to untreated controls. The treatment of oriental fruit flies with cuelure also reduced their mating to a lesser extent. These results do not yet provide the practical proof of this new concept for pest management, but other model systems may be more appropriate. This work is novel in presenting attractants on a moving target, in this case, another insect species.

Implication of SAR of male medfly attractants in insect olfaction.

Medfly (Ceratitis capitata) males are strongly attracted by different compounds, not described as pheromones. The best attractants reported are (+)-alpha-copaene, a sesquiterpene of natural source and (-)-ceralure-B1, a non-natural iodinated cyclohexane ester. Although their origin, atomic composition, chemical and physical properties are rather different, they show similar attraction to medflies. The question of why these compounds, act behaviorally in the same way, has been never addressed in research papers. We show here for the first time that these compounds have quite similar stereochemistry, water accessible surfaces, certain local dipole moments and, to some extent, similar octanol/water partition coefficient (log P). When seven carbons, one oxygen and one iodine belonging to (-)-ceralure-B1 are selectively chosen based on topological homology with (+)-alpha-copaene and are overlaid with nine corresponding carbons of (+)-alpha-copaene, the RMS is 0.367 A. This represents a high degree of steric resemblance. Local dipole moments and charges are similar in those regions where the molecules show topological homologies. Thus, we hypothesize that these two molecules could interact with the same male medfly's odorant receptor(s). The implications of this result in future research in insect olfaction is discussed.

Field attraction of Mediterranean fruit fly, Ceratitis capitata (Wiedemann) to synthetic stereoselective enantiomers of the ceralure B1 isomer.

Stereoselectively synthesized enantiomers of ethyl cis-5-iodotrans-2-methylcyclohexane-1-carboxylate (ceralure B1), a potent lure for male Mediterranean fruit flies, were tested in the laboratory and the field against laboratory reared sterile flies. The (-)-ceralure B1 enantiomer was significantly more attractive than the (+)-ceralure B1 antipode. Dose-response studies of the above compounds demonstrated that (-)-ceralure B1 and to a lesser extent, racemic ceralure B1, captured consistently more male flies than trimedlure, the current male attractant used in detection programs. Longevity tests demonstrated that, over a three-week period, both (-)-ceralure B1 and racemic ceralure B1 caught significantly more flies than trimedlure. The synthesis of specific enantiomers of ceralure B1 shows great promise as a male attractant that could replace trimedlure for detection and delimitation in action programs aimed at this exotic pest.

Attraction of female mediterranean fruit flies to the five major components of male-produced pheromone in a laboratory flight tunnel.

Attraction and pheromonal activity of five major identified components of the male-produced sex pheromone of the Mediterranean fruit flyCeratitis capitata to virgin laboratory-reared females was assessed in a laboratory flight tunnel. Dual-choice competitive assays were run to establish a baseline response of virgin females to live male pheromone, individual components, and an ensemble of all five compounds alone (air control) and competitively against one another. Approximately 50% of the females released in the tunnel were captured on leaf models emitting pheromonal odors from five live males. Over 37% of released females responded to an ensemble of five major identified components presented in individual capillaries. Response of females to individual components was less than 10%. Competitive assays showed the live male-produced pheromone to be more attractive than either the five major component ensemble (FMCE) or individual components. Further research is likely to identify other male-produced compounds with pheromonal activity that could improve development of a pheromone-based trap for monitoring Mediterranean fruit fly populations.

Heat shock proteins and thermotolerance in a cultured cell line from the Mediterranean fruit fly, Ceratitis capitata.

Heat shock proteins (hsps) were identified in a cell line from the Mediterranean fruit fly, Ceratitis capitata Wiedemann (Diptera: Tephritidae) exposed to elevated temperatures. Cells produced three hsps (Mr 87,000, 69,000, and 34,000) in response to a temperature shift from 26 degrees C to 37 degrees C (30-60 min) with a concomitant decrease in synthesis of most other cellular proteins. Synthesis of low Mr hsps was not evident. The heat shock response is triggered within 30 min at temperatures from 33 degrees C to 41 degrees C. At temperatures greater than 41 degrees C protein synthesis was shut down. Within 2-3 h after return to 26 degrees C, synthesis of proteins repressed at the higher temperatures resumed production while the major hsps disappear. Heat shock proteins were not produced in the presence of actinomycin D. Evaluations on the role of hsps in conferring thermotolerance to the cells showed an increase in cell viability in heat-shocked cells over non-heat-shocked cells (after 3 and 10 days) when subsequently placed at 45 degrees C for 1 h, a normally lethal temperature. Heat shock alone had little effect on subsequent cell viability or growth at 26 degrees C. These results suggest that hsps produced by these cells may aid in the maintenance of cell integrity and thus play a transitory role in thermotolerance.

Electroantennogram responses of mediterranean fruit fly,Ceratitis capitata (Diptera: Tephritidae) to trimedlure and itstrans isomers.

Electroantennograms (EAGs) of unmated laboratory-reared male and femaleCeratitis capitata (Wiedemann) were recorded in response to the attractant trimedlure [tert-butyl 4(and 5)-chloro-trans-2-methylcyclohexane-1-carboxylate] and its fourtrans isomers. For both sexes, the magnitude of the EAG response was relatively low as compared to other previously tested compounds (i.e., plant volatiles). Dosage-response curves generated for all TML isomers revealed that flies responded to increasing dosages over a relatively narrow range (two to three log steps). Responses for both sexes peaked at ca. 10 µg dose for all isomers. Antennal response in males was greatest to the C isomer followed by the B1, A, and B2 isomers, while responses of females were greatest for the A isomer followed by B1, C, and B2. Both sexes exhibited a long recovery period for the response potential to return to baseline at doses above 1 µg for all of the isomers tested, except for B2. The low EAG sensitivity to trimedlure and the apparent EAG selectivity to the C isomer in males are discussed in relation to the known field attractancy of males to the C, A, B1, and B2 isomers.

Electroantennogram responses of the mediterranean fruit fly,Ceratitis capitata, to a spectrum of plant volatiles.

Electroantennograms (EAGs) were recorded from unmated, laboratory-reared, male and femaleCeratitis capitata (medfly) in response to a range of C1 and C2 to C12 carbon chain-length aliphatic alcohols, aldehydes, acetates, and acids, and lactones, some of which are known volatiles from leaves and fruits. A large degree of EAG response uniformity between the sexes was observed, with only eight of the 70 compounds tested eliciting significantly larger amplitude EAG responses from female than male antennae. In general, for the five functional-group series tested, aldehydes and alcohols elicited greater responses than acetates, lactones, and acids. The unsaturated alcohols, aldehydes, acetates, and acids elicited equal or larger amplitude EAG responses than their comparable saturated compounds. For four of the functional-group series tested, the EAG response amplitude was significantly greater for a particular carbon chain length, with responsiveness to primary alcohols and aldehydes peaking at C6, acids peaking at C5-6, and acetates peaking at both C5 and C8. The EAG responses to both the 2- and 3-position monoenic alcohols peaked at C6 and C8, while the secondary alcohols peaked at C7. The greatest EAG responses of all compounds tested were elicited by monoenic C6 alcohols and aldehydes that are constituents of the "general green-leaf odor" that emanates from most plants. The potential adaptive benefit of selective sensitivity to green-leaf volatiles is discussed in regard to foraging behavior of medflies.