The biology of the afrotropical Conchyloctenia hybrida Boheman on Solanum campylacanthum subsp. panduriforme was studied under laboratory conditions in South Africa. Papery oothecae contained between 2 and 10 eggs. Adults displayed vigorous feeding, high fertility, longevity, as well as careful choice of oviposition site. Construction of oothecae was highest at the junctions of main and lateral veins on abaxial leaf surfaces facing upwards or downwards and adaxial surfaces facing downwards. The period from oviposition to adult eclosion ranged between 37 and 42 d at 25°C. Adults had an even sex ratio. After a preoviposition period of 34 d, females deposited 3 to 48 oothecae in 4 to 91 d. The mean longevity of females and males was 168 and 165 d, respectively. The net replacement rate was 50.14, the intrinsic rate of natural increase was 0.97 per month, the mean generation time was 4 mo, and doubling time was 0.71 mo. Daily consumption rate of leaves increased rapidly in late larval instars and was highest for adults. Adults underwent a series of elytral color changes corresponding with age and physiological state. Mature adults characterized by hardened metallic-colored elytra had a higher winter survival rate than young adults with soft, nonmetallic elytra.
Plant morphological changes mediated by growth conditions are linked to changes in host preference of herbivores. Understanding how these morphological changes inßuence herbivore feeding is critical in the interpretation of results of host evaluation of candidate weed biocontrol agents in quarantine and improvement of the evaluation system. We determined the effect of plant growth conditions on leaf trichomes and host choice of Conchyloctenia hybrida Boheman, an insect adapted to the removal of trichomes before feeding. The study included four Solanum species: Solanum lichtensteinii Willdenow (natural host of C. hybrida), Solanum mauritianum Scopoli, Solanum melongena L., and Solanum tuberosum L.. Plants were grown in either full sun, shade, a glasshouse, or in a growth-chamber. Plants grown in full sun had a higher leaf trichome density than those in shade or controlled environments. S. mauritianum had the highest trichome density and thickness of trichome layer. In a multiple-choice test using excised leaves, feeding by C. hybrida was higher on Solanum plants grown in the controlled environment as compared with full sun. Trichome removal from leaf surfaces of plants grown in full sun, using adhesive tape, was effective for S. lichtensteinii, S. mauritianum, and S. melongena, but not S. tuberosum. Leaf consumption by C. hybrida increased signiÞcantly where manual trichome removal using adhesive tape was effective. Structurally, leaves of S. tuberosum have simple trichomes with basal cells sunken into the mesophyll tissue. When using forceps to remove trichomes of S. tuberosum, mesophyll and vascular tissue remained attached to the trichomes. Generally, the type, density, and mat-thickness of leaf trichomes determined feeding by C. hybrida, but varied with plant species and growth conditions.
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