Diminished fitness of red cotton bug Dysdercus koenigii Fabricius induced by the volatiles in the hexane extract of Catharanthus roseus

Survival, longevity, growth index and development of fifth instar nymphs of Dysdercus koenigii (Heteroptera: Pyrrhocoriedae) as influenced by the Catharanthus roseus was assessed in the present investigation. The fifth instar nymphs were exposed to the volatiles present in the extract for 24 h. Different concentrations of the extract ranging from 0.00625% to 10% were used for the treatment. The results indicate that the survival of treated nymphs was not affected significantly. However, the volatiles present in the extract influenced the growth and development of the treated fifth instar nymphs. The nymphs exhibited decreased growth as reflected by the decrease in growth index. The extract induced different types of developmental anomalies notably incomplete moulting, supernumerary instars, adultoids and adults with deformed wing. In some cases, exuviae did not detach from the body of the adults and create obstacle in the feeding, walking and mating. The effects of the extract on nymphal development were also dose-dependent. No normal adults could develop in the treatments with the concentration 5% or more; various morphological and developmental abnormalities were reported in the nymphs treated with 2.5% to 0.1% of the extract. GC-MS analysis of the hexane leaf extract of C. roseus showed the presence of sesquiterpenes including geranylgerniol and many toxic chemicals. These phytoconstituents of the C. roseus extract besides having cidal effects also showed juvenile hormone mimic activities which impair lifetime fitness of D. koenigii. Therefore, botanical from the C. roseus can potentially be used as an alternative approach in pest management.