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Exochomus troberti Mulsant (Coleoptera: Coccinellidae): A predator of cassava mealybug, Phenacoccus manihoti Mat-Ferr (Homoptera:Pseudococcidae) in southeastern Nigeria
Published online by Cambridge University Press: 19 September 2011
Abstract
The developmental periods of the immature stages of Exochomus troberti Mulsant were studied in the laboratory at the prevailing temperature range of 26–30°C. That of the second instar larva was the shortest (2.1 days) followed by the third instar larva (3.1 days). The longest developmental period (approximately 5 days) was recorded for the egg, first- and fourth-instar larvae and pupa.
Oviposition commenced after 1 week of adult life and peaked in the 5th week with 37.2 female eggs/female. All ovipositing females survived the first 9 weeks of adult life when 82% of the total eggs were laid. By the 13th week, which was the effective end of reproduction (98 % fecundity) only 40% of the females had died.
Both capacity for increase (rc) and intrinsic rate of increase (rm) were calculated for E. troberti and found to be 0.092/day and 0.105/day, respectively.
Mean daily predation rates in non-choice experiments on the second instar nymphs of P. manihoti by the fourth, third and second instar larvae of E. troberti were 28.3, 15.6 and 8.0, respectively. On the third instar nymphs and fourth instar young adults of P. manihoti the mean daily predation rates by the fourth, third and second instar larvae of E. troberti Were 17.6, 8.3 and 4.5; and 4.0, 3.0 and 1.0, respectively.
The populations of E. troberti, other coccinellid predators and P. manihoti were monitored in two small local farms for three seasons. E. troberti was found to be the dominant coccinella predator in terms of numbers of individuals found in the field during the years of this experiment.
The cyclical population oscillations of P. manihoti were similar in all the experimental years but differed only in the amplitude of oscillations. Those of E. troberti and the other coccinellid predators were lower than those of P. manihoti.
Résumé
Les périodes developpement des stades larvaires chez Exochomus troberti Mulsant ont été étudiées dans le laboratoire à la température amblarte comprise entre 26 et 30°C. Celle de la larve du deuxième stade fut la plus courte (2, 1 jours) suivie de la larve de troisième stade (3, 1 jours). La plus longue durée de developpement (environ 5 jours) a été notée pour l'oeuf, la larve du premier et quatrième stade et la pupe.
L'oviposition a commencé après un semaine de vie adulte et le pic a été achévé dans la cinquième semaine avec 37, 2 oeufs femelles/femelle. Toutes les femelles en oviposition ont survecu les neuf premières semaines de vie adulte, alorsque 82 % de la totalité des oeufs ont été pondus. Lors de la 13e semaine qui était la fin effective de la reproduction (98% de fecondité) seulement 40% des femelles étaient mortes.
La capacité d'accroisement (rc) et la taux intrinsèque d'accroisment (rm) ont été calculés chez E. troberti et furent respectivement 0,092/jour et 0,105/jour. La déstruction moyenne quotidienne des nymphs du deuxième stade de P. manihoti par les larves du quatrième, troisième et deuxième stade de E. troberti était respectivement 28, 3, 15,6, et 8,0. Sur les nymphs du troisième, stade et les jeunes adultes du quatrieme stade des P. manihoti, la destruction moyenne quotidienne par les larvesdu quatrième, troisième, et deuxième stade de E. troberti étaient respectivement 17,6,8, 3, et 4,5; et 4,0, 3,0 et 1,0.
Les populations de E. troberti, des autres prédateurs coccinellidés et de P. manihoti ont été observées dans deux petites fermes locales pendant trois saisons. Les souches de E. troberti sont apparus comme les prédateurs dominants en fonction du nombre des individus trouvés sur place pendant la durée de cette experience.
Les cycles d'oscillations de la population chez P. manihoti étaient similaires lors de chaque année d'expérimentation mais différaient seulement par l'amplitude des oscillations. Ceux de E. troberti et des autres prédateurs coccinellidés étaient plus bas que ceux du P. manihoti.
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References
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