Effects of corn pollen chemistry, dietary proteinase inhibitors and beetle oral secretions on feeding behaviors and fecundity of adult western corn rootworm

Sugars (melezitose, maltose, sucrose, raffinose and fructose), for the first time, were found to be significant feeding stimulants for adult western corn rootworm (WCR). However, feeding responses to combinations of amino acids, sugars, or amino acids plus sugars were lower than that of the sum of responses to individual components, suggesting that antagonistic interactions occur between sugars and amino acids at adult WCR taste receptors. Age-, sex- and population-dependent feeding responses to sugars and amino acids were highly variable. Beetle feeding was enhanced additively upon combination of these amino acids and sugars with a flavonol diglycoside in corn pollen extract (CPE). However, an equivalent combination of sugars and amino acids with a flavonol diglycoside reconstituted only about 75% of the phagostimulation elicited by CPE, indicating that additional phagostimulatory factors are present in CPE. Low molecular weight peptidyl proteinase inhibitors (PIs) (e.g. leupeptin) were potent antifeedants for adult WCR. The roles of sulfhydryl groups in taste chemoreception for adult WCR remains elusive. The total concentration of 17 amino acids present in beetle oral secretion (OS) was less than 3 nmol while two stimulatory sugars for adult beetles, sucrose and fructose, were not detected. Total phagostimulation by free amino acids and sugars in natural foods of WCR would not be affected significantly by addition of these phagostimulants in its OS. Cucurbitacins and sucrose were degraded by hydrolysis after contact with OS for 30 min on filter paper disks. Significant correlations were found in concentrations and profiles of free amino acids between OS, midgut fluid (MF) and hemolymph. E-64 and calpeptin were the strongest PIs to proteolytic activities and cysteine proteinases predominate in both MF and OS of adult WCR. The most significant effect of cysteine PI consumption on adult female WCR was reduced fecundity. Beetle fresh weights were also reduced by consuming PIs. Supplementation of the E-64-treated pollen diet with ten essential amino acids enhanced up to 3.7-fold the number of eggs laid and up to 2.2-fold the survival rate of female WCR. Thus, egg production appears highly dependent on supply of essential amino acids from corn pollen proteolysis.