Structure-activity relationships of naphthalene and 10 related compounds on Coptotermes formosanus (Isoptera: Rhinotermitidae)
Naphthalene and ten derivatives were evaluated for initial and residual toxicity, route of penetration and speed of toxic action on C. formosanus. In no-choice treated filter paper assays using two colonies, 1′- and 2′-acetonaphthone had the greatest contact toxicity followed by 1- and 2-methoxynaphthalene; toxicity of these chemicals was 7- to 38-fold greater than naphthalene. 2, 7- and 2, 6-diisopropylnaphthalene were 4- to 11-fold less toxic than naphthalene. For all chemicals tested, the colony collected from Lake Charles, LA, was more tolerant than that collected from New Orleans, LA. When termites placed on filter papers treated with the estimated 24 h LC90s, 2′-acetonaphthone followed by 1-methylnaphthalene and 1′- acetonaphthone were the fastest acting toxicants killing 50% of workers after ≤ 5 h compared to 16 h with naphthalene. Workers responded faster than soldiers to 1′-acetonaphthone and both responded similarly to 2′-acetonaphthone. At the estimated concentrations for 90% contact mortality, termite mortality via inhalation was not significantly different from the controls in 1′-acetonaphthone, 2′-acetonaphthone and 2-naphthalene methanol treatments. Naphthalene, 2-isopropylnaphthalene, 1- and 2-methylnaphthalene and 1- and 2-methoxynaphthalene were highly volatile causing 61% to 100% termite mortality via their toxic fumes. In no-choice treated sand assays at 100mg kg-1, 1′-, 2′-acetonaphthone, 1-, 2-methoxynaphthalene and 2-naphthalene methanol were effective toxicants. 1′- and 2′-acetonaphthone maintained their initial toxicity when 1-month residual activity was evaluated. Acetyl substitutions altered the physical and chemical properties of naphthalene moiety to low volatility, more contact toxicity, fast action, and long persistence. This study points to the potential value of 1′- and 2′-acetonaphthone in termite control programs. © 2009 American Chemical Society.