Oviposition Preference of Sweetpotato Weevil on Three Sweetpotato Varieties

Sweetpotato weevil, Cylas formicarius elegantulus (Summer), is the most detrimental pest of sweetpotato, Ipomoea batatas (L.) Poir, in the world.  Weevil larval tunneling and adult feeding induces terpene production, rending the storage root inedible.  Sweetpotato varieties with resistance to sweetpotato weevil have been actively bred for by the LSU AgCenter Sweetpotato Breeding Program.  In no-choice assays, sweetpotato weevil adult emergence from cv. Murasaki is 25% that of cv. Beauregard.  However, adult weights, sex ratio, and lengths were not affected; providing evidence that larval mortality is not the cause for reduced adult emergence.  To better elucidate the exact mechanism of resistance, oviposition preference experiments were conducted on three commercial varieties of sweetpotato; Beauregard, Evangeline and Murasaki, under laboratory conditions.  Six gravid female lab-reared weevils were released per root of each variety in a no-choice test, 10 roots per replicate, replicated three times.  Females were given five days to lay eggs after which they were removed.  Number of eggs oviposited on each root was counted.  Murasaki had significantly lower number of eggs oviposited as compared to the other two varieties.  Preliminary data indicates that sweetpotato weevil resistance found in Murasaki is due to non-preference.