Analysis of biological control of cassava pests in Africa. II. Cassava mealybug Phenacoccus manihoti.

Abstract

The effects of natural enemies and rainfall on the population dynamics of the pseudococcid Phenacoccus manihoti, and the effects of P. manihoti on the growth, development and yields of cassava as modified by weather, soil water, nitrogen and natural enemies were examined using a simulation model. Predicted yield losses in wet years were small because rainfall suppressed the population of P. manihoti directly and enhanced the ability of the plant to compensate for the feeding damage. In contrast, losses in dry years were higher because of direct negative effects of water stress on photosynthesis and were compounded by the much larger population of P. manihoti which developed. The model confirmed field observations in Nigeria that the introduced encyrtid parasitoid Epidinocarsis lopezi is the most important factor controlling populations of P. manihoti in the dry season, and rainfall, directly or possibly via diseases, during the rainy season. The contribution of indigenous coccinellid predators, Hyperaspis and Exochomus, to the mortality of P. manihoti was mostly dispensible and possibly slightly disruptive. It is concluded that Epidinocarsis lopezi regulates P. manihoti in Nigeria despite the disruptive effect of rain-induced mortality, drought effects on host abundance and predation by native coccinellid beetles.

Key words

• agricultural entomology
• arthropod pests
• beneficial arthropods
• beneficial insects
• beneficial organisms
• biological control
• biology
• cassava
• control
• crops
• ecology
• Environmental factors
• fields
• Insect pests
• models
• mortality
• natural enemies
• parasites
• Parasitoids
• pest control
• pests
• population dynamics
• predators
• Predatory insects
• prey
• rain
• root crops
• Simulation models
• Techniques
• vegetables
• yield losses