SEASONAL RESPONSE TO PHENYLPROPANOID ATTRACTANTS BY NORTHERN CORN-ROOTWORM BEETLES (COLEOPTERA, CHRYSOMELIDAE)

Attraction of adult northern corn rootworms, Diabrotica barberi Smith and Lawrence, to yellow sticky traps baited with one of a series of structurally related phenylpropanoids (100 mg/trap) was examined by sex at four stages of crop development in two commercial maize fields in South Dakota. Attractant treatments were laid out in a randomized complete block design during favorable weather in 1993 when maize stage was late vegetative (V10+, 8/2-8/4, Field 1), silking (R1, 8/11-8/13, Field 1), late blister to early milk (R2-R3, 8/24-8/26, Fields 1 and 2) and late milk to early dough (R3-R4, 9/1-9/3, Fields 1 and 2). Significant attraction to phenylpropanoid-baited traps occurred during all maize stages tested, except silking (R1), when counts of beetles on plants and direct observation of beetle activity nevertheless indicated the continued presence of northern corn rootworm adults. The highest captures occurred late season (R3-R4). Females were generally more responsive than males, considering their lower numbers on control traps. Ranking of the relative attractiveness of the test compounds to females was similar across seasons (silking omitted) and fields: cinnamyl alcohol greater than or equal to 3-phenyl-1-propanol and hydrocinnamaldehyde (phenylpropanaldehyde) greater than or equal to trans-cinnamaldehyde greater than or equal to 4-propylphenol. Ranking was also similar between sexes, although only the first three compounds attracted significantly more males than did controls. Neither sex found 3-(4-hydroxyphenyl)-1-propanol attractive.