Larval growth of Diaprepes abbreviatus (Coleoptera : Curculionidae) and resulting root injury to three citrus varieties in two soil types

Larval growth and intraspecific competition of Diaprepes abbreviatus (L.) l arvae and consequent root injury in container-grown citrus in the greenhous e were evaluated. Roots of Carrizo citrange, Citrus sinensis L. Osbeck X Po ncirus trilfoliata (L.) Raf.: Cleopatra mandarin, C. reticulata Blanco, and Swingle citrumelo, C. paradisi Macf. X P. trifoliata (L.) Raf. rootstock s eedlings grown in Candler fine sand and potting soil were colonized with di fferent populations of D. abbreviatus larvae. Larvae were exposed to the se edlings for 79 d. Larval growth and development increased steadily for appr oximate to 70 d on all rootstock-soil combinations, at which time most larv ae were instars 6-8. Most feeding injury occurred to roots when larvae were between instars 3 and 6. Larval weight reached a plateau at approximate to 70 d, but often declined between 70 and 79 d. When larvae were small, inju ry to seedlings developed slowly, primarily on fibrous roots, then feeding increased rapidly, often resulting in total consumption of both fibrous roo t and bark tissue. Although not statistically significant, root injury deve loped slightly slower on Swingle citrumelo compared with Carrizo and Cleopa tra rootstocks. but damage was comparable by 79 d. Little or no difference in consumptive benefit to the larvae was found between the rootstocks. Base d on larval weight days, little feeding injury occurred during the first 21 d, but increased rapidly between 21 and 60 d. Soil type affected the rate of larval growth and development, with potting soil contributing to greater growth rates. Detritus in potting soil provided little or no nutritional r esource, suggesting that the effect of patting soil on larval development w as primarily physical. In addition, fewer inoculated larvae per seedling ex hibited greater weight gains than higher infestation densities, suggesting that intraspecific competition for nutritional resources influenced larval development.