Resistance of Citrus Rootstocks and Glycosmis pentaphylla Against Larval Diaprepes abbreviatus (Coleoptera: Curculionidae) in Live Root or Diet-Incorporation Assays

Abstract

s The growth of larval Diaprepes abbreviatus L. was measured after rearing them on roots of rutaceous seedlings for 35 or 42 days. Larvae were fed on seedlings of two common citrus rootstocks, two new hybrids that are under development as rootstocks, and one citrus relative. Live weights of larvae reared on Carrizo or Swingle rootstocks for 42 days increased an average of 10.3- and 10.2-fold, respectively; weight increases on the citrus hybrids HRS-802 and HRS-896 for 35 days averaged 7.6- and 6.1-fold, respectively; and weight increase on Glycosmis pentaphylla Retzius for 42 days averaged 2.5-fold. A bioassay to test for potential phytochemical sources of resistance against the larvae was developed by incorporating finely milled roots into larval diet. Milled root samples were incorporated into a standard semi-defined diet at 5% concentrations (w/v), and growth of larval weevils was recorded following a 32-day feeding period. Roots collected from uninfested control seedlings in the previous experiment were used. On diet containing no roots, mean larval weight increased 16.8-fold, while weights increased 13.9-fold on diet containing roots of Carrizo, 12.0-fold on Swingle, 15.1-fold on HRS-802, 12.3-fold on HRS-896, and only 5.5-fold on G. pentaphylla. Both tests indicate that G. pentaphylla may represent a source of root resistance to D. abbreviatus, and the diet-incorporation tests indicate potential phytochemical or microbial sources of resistance.