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.) larvae and consequent root injury in container-grown citrus in the greenhouse were evaluated. Roots of Carrizo citrange, Citrus sinensis L. Osbeck × Poncirus trifoliata (L.) Raf.; Cleopatra mandarin, C. reticulata Blanco, and Swingle citrumelo, C. paradisi Macf. × P. trifoliata (L.) Raf. rootstock seedlings grown in Candler fine sand and potting soil were colonized with different populations of D. abbreviatus larvae. Larvae were exposed to the seedlings for 79 d. Larval growth and development increased steadily for ≈70 d on all rootstock-soil combinations, at which time most larvae were instars 6–8. Most feeding injury occurred to roots when larvae were between instars 3 and 6. Larval weight reached a plateau at ≈70 d, but often declined between 70 and 79 d. When larvae were small, injury to seedlings developed slowly, primarily on fibrous roots, then feeding increased rapidly, often resulting in total consumption of both fibrous root and bark tissue. Although not statistically significant, root injury developed slightly slower on Swingle citrumelo compared with Carrizo and Cleopatra rootstocks, but damage was comparable by 79 d. Little or no difference in consumptive benefit to the larvae was found between the rootstocks. Based 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 resource, suggesting that the effect of potting soil on larval development was primarily physical. In addition, fewer inoculated larvae per seedling exhibited greater weight gains than higher infestation densities, suggesting that intraspecific competition for nutritional resources influenced larval development.