Influence of Nutritional Characteristics of Selected Corn Genotypes on Food Utilization by the Rice Weevil (Coleoptera: Curculionidae)l

Protein. starch. fat. sucrose. glucose. and fructose contents were analyzed in 22 com genotypes and correlated with food utiliz'ltion panlmeters and indices determined on developing rice weevil. Sirophillls 01}'zae (L.), reared on each com genotype. The larval period was reduced and heavier pupae developed from com with higher glucose content. Increascd levels of prOiein reduced amount of food consumed and increased food utilization efficiency. Larv,le reared on pelletized. germless kernels required a longer time to reach pupation, had lower pupal weights and lower food utilization efficiency than did larvae reared on pellctized whole kernels. However. mortality was similar in both treatments indicating that nutrients found in the germ were not essential. A homogenous distribution of nutrients in the food reduced larval developmcnt time and increased food utilization efficiency. To better understand the relationships of an insect pest to its host. several arcas of study including nutrition must be considered. There is relatively little information about the influence of major groups of nutrients found in com kernels on the development of the rice weevil, SilOphilus ory:ae (L.). Singh and McCain (1963) found that field infestation and number of offspring were positively correlated with sugar and starch contents of com hybrids but neither fat nor protein seemed to affect com susceptibility or development of the rice weevil (RW). Singh et al. (1972) found that protein content was not related to resistance. but Dobie (1977) observed that protein content was negatively correlated with a susceptibility index. McCain and Eden (1965) indicated that susceptibility of com inbred lines to RW attack. expressed as number of live adults after a 2-month infestation. was positively correlated with the percentage of reducing sugars. but not with total sugar content. Rhine and Staples (1968) suggested that percentage of amylose found in the starch portion influences sus~ ceptibility of com to rice weevil. Chippendale (1972) concluded that adult weevils survived in diets containing ca. 70% cereal starches, dextrins. amylopectin. or glycogen, but died prematurely when the diets contained 70% amylose. cellulose. inulin. or monoor disaccharides. Carbohydrates that did not allow survival acted as feeding deterrents without causing digestive enzymatic lesions. Richards (1944) reported that germ tissue is toxic to Ist-instar larvae of the rice weevil. Schoonhoven et al. (1974) showed that additions of small amounts of extra germ tissue to pellets made of ground com increased the number of progeny and weight and shortened the de1JOint contribution: KentuckY State Unh·ersltv. Unlversitv (If Kentucky, and USDA Northern Regionul Research Liborlllol')'. This investigation wus supported in purt by u USDAtCSRS grant to Kentucky StUle Unlvcr:;ity under agreement KYXI28tOOOOO4. ami this paper (No. 82-7-]-25::!) is also in connection With a project urthe KeOlUck)' Agriculluml E:o;perimenl Station. Received for publication 22 October 198::!; ilccepted::!5 April 1983. 1Kcnlucky State University. Frilnkfort. KY 40601. -'University of Kentucky. Lcxingllln. KY 40540-0091. ~Northcm Regionill Research Labor:Jtol')', Peoria. IL 61604. velopment time. Numbers of progeny and weight were reduced by adding larger amounts of germ tissues. Gomez et al. (1982) conducted food utilization studies of the RW on 17 com genotypes. Hybrids induced longer developmental periods and lighter pupae and were utilized less efficiently than inbred lines. Large amounts of amylopectin determined by the W\' gene shortened time to pupation llOd increased the efficiency of food utilization. A meridic diet was the most suitable type of food for larval RW development. The main objective of this study was to determine how larval development and food utilization of the RW may be influenced by varying levels of the major nutrient classes in selected corn genotypes. Concomitant objectives were to study the influence of germ nutrients and nutrient distribution within the corn kernel on larval development and food utilization. Materials and Methods Food Urili:arioll Variables alld NlI1rirional COlllefll Twenty~two corn genotypes were used to study relationships between major nutrient components and food utilization parameters and indices. The genotypes were the 17 used by Gomez et al. (1982). with the addition of the following five genotypes: one susceptible inbred line. (H60): two synthetic varieties (" Alexho." containing high oil. and HMo10~. a synthetic containing the op2 gene). and tlVO hybrids (1<806 x B37. an intermediate oil level hybrid. and B37 x tvl0 17, a widely grown hybrid with low oil content). H60 was categorized dsusceptible" when it was compared with inbred A619 in no~choice oviposition tests (Gomez et al. 1983L Methods used for determination of oil and protein were those of Link (1973). A method utilizing high~ pressure liquid chromatography (HPLC) with gel filtration was used for sugars. Relationships between nutritiomli contents (independent variables) and v'lriables measured and calculated (dependent variables) were ex~ amined by simple correlation analysis (SAS program) and by the SAS stepwise max-r1 improvement method. Data recorded by Gomez et al. (1982) corresponding to mean number of adult rice weevils attracted to corn genotypes presented in cups (free-choice test) and mean number of eggs oviposited per cup of 40 kernels (no