Trapping sweetpotato weevil, Cylas formicarius elegantulus (Coleoptera: Brentidae), with high doses of sex pheromone: Catch enhancement and weathering rate in Hawaii

Authors: McQuate, Grant; Sylva, Charmaine

Submitted to: Hawaiian Entomological Society Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2014
Publication Date: 12/31/2014
Citation: Mcquate, G.T., Sylva, C.D. 2014. Trapping sweetpotato weevil, Cylas formicarius elegantulus (Coleoptera: Brentidae), with high doses of sex pheromone: Catch enhancement and weathering rate in Hawaii. Hawaiian Entomological Society Proceedings. 46:59-69.

Interpretive Summary: Sweetpotato, Ipomoea batatas (L.) Lamarck, is one of the top ten staple crops produced worldwide. Among the nations of the world, the United States is the 12th greatest producer of sweetpotatoes, with production greatest in the states of North Carolina California, Mississippi and Louisiana. Sweetpotato is also produced in Hawaii where its production has been increasing in recent years. The sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), is a major quarantine pest of sweetpotato in Hawaii as well as a pest of concern in all parts of the tropics where sweetpotatoes are grown. Sweetpotato weevil infestation can reduce marketable root yield as well as reduce root quality through induction of production of bitter tasting compounds by the sweetpotato tissue. A female produced male lure [(Z)-3-dodecenyl (E)-2-butenoate] has been identified and is commercially available. The use of many traps baited with a high dose of this lure (“mass trapping”) has been shown to reduce sweetpotato weevil field populations and associated root damage. Recent research has shown that adding a green light source to a trap baited with a high dose of the male lure can increase trap catch over 4-fold. In order to prepare for field assessment of the use of mass trapping as a means of reducing sweetpotato weevil damage to sweetpotato roots produced in Hawaii, research was conducted to document the effectiveness and longevity of attraction, under Hawaiian growing conditions, of traps having a high dose of the male lure. Traps baited with fresh male lure (dose = 1.0 mg) caught over 22 times as many weevils as traps baited with 12 µg lure (the dose commonly used for monitoring sweetpotato weevil populations) over an initial one week trapping period. Trap catch, though, declined to 50% of fresh attractiveness 19.0 weeks after first deployed. Based on this weathering rate, traps baited with a 1.0 mg dose of male sweetpotato weevil lure would need to have two fresh charges over the course of the production cycle in Hawaii in order to maintain catch at a rate of at least 50% of the catch rate at traps baited with of fresh lure. Further research is needed to test the effectiveness of mass trapping in reducing root damage by sweetpotato weevil, through the use of a high dose male lure in combination with the recently reported enhancement of trap catch by adding a green light source.

Technical Abstract: Sweetpotato, Ipomoea batatas (L.) Lamarck, one of the top ten staple crops produced worldwide, has increased in production in Hawaii in recent years. The sweetpotato weevil, Cylas formicarius elegantulus (Summers)(Coleoptera: Brentidae), is a major economic and quarantine pest of sweetpotato in Hawaii as well as a pest of concern in all parts of the tropics where sweetpotatoes are grown. Sweetpotato weevil infestation can reduce marketable root yield as well as reduce root quality by inducing production of bitter tasting sesquiterpines by the sweetpotato tissue. Traps baited with a male sweetpotato weevil lure, (Z)-3-dodecenyl (E)-2-butenoate, can be used for population monitoring, or even for population suppression if mass trapping is done using high doses of this lure. Weathering rates, though, have not been documented in Hawaii for the higher septa loadings (100 to 1000 µg [=1.0 mg]) that have been proposed for use in population suppression efforts through mass trapping. Here, we present comparative catch rates and weathering rates, along the Hamakua Coast of Hawaii Island, of traps baited with septa loaded with 12 µg, 120 µg or 1.0 mg of male sweetpotato weevil lure. Traps baited with fresh 1.0 mg male lure caught over 22 times as many weevils as traps baited with 12 µg lure over an initial one week trapping period. Based on a fitted decay curve, decline in attractiveness of the 1.0 mg treatment to 50% of fresh attractiveness occurred at 19.0 weeks, while the 120 µg treatment showed a 50% decline after 16.3 weeks, under climate conditions on the Hamakua Coast of Hawaii Island. Further research is needed to test the effectiveness of mass trapping in reducing root damage by sweetpotato weevil, through the use of a high dose male lure in combination with the recently reported enhancement of trap catch by adding a green light source.