- Vegetables: cabbages
- Pest Management: general pest management
The diamondback moth (DBM), Plutella xylostella (L.), is the primary pest of cabbage and related crops in the family Brassicaceae. Insecticide resistance in diamondback moth populations is a major factor limiting cabbage production worldwide. Biological control offers an alternative to insecticides, but little is known of whether multiple natural enemies have additive, antagonistic, or synergistic effects on DBM populations.
Therefore, we evaluated interactions between Cotesia plutellae (Kurdj.), an important specialist parasitioid of the diamond back moth, and Podisus maculiventris (Say), an important generalist predator of numerous agricultural pests, and their effect on DBM populations.
First, we evaluated the seasonal activity of the predator P. maculiventris in North Florida to determine its potential in influencing DBM populations and alternate natural enemies. The seasonal activity of P. maculiventris overlaps with that of DBM, suggesting that P. maculiventris could have a significant effect on DBM populations.
To determine how P. maculiventris and C. plutellae interact, we studied their combined effect on DBM populations and consequent plant damage. Often when a predator and parasitoid are present together the predator prefers to feed on parasitized pest larvae rather than unparasitized ones, which interfere with the parasitoid’s ability to control a pest species and can release the pest from an acceptable level of control. In lab trials, we found that P. maculiventris does preferentially attack parasitized larvae. In field cage trials, we found that C. plutellae reduce DBM populations and plant damage, but this control is not enhanced by the addition of P. maculiventris. These results indicate the importance of evaluating interspecific interactions to optimize biological control.
Temporal Occurrence of Natural Enemies
Determining the seasonal activity or temporal occurrence of a pest and a potential predator or parasitoid is an important factor to quantify for optimizing biological control. The proportion of seasonal overlap between a pest and potential natural enemy may be indicative of the influence that predator or parasitoid has on pest populations.
Prey preference is a situation in which a predator selects one type of prey more frequently than another type of prey. Research has shown that behavior, locality, morphology, density, ontogeny, environmental temperatures, and/or physiology of the prey or natural enemy influence prey preference and prey selection. The beneficial impact of a parasitoid on a pest may be reduced if predators prey more on parasitized prey than on unparasitized prey. This preference could release the pest from an economically acceptable level of control by a parasitoid, especially when the predator’s attack rate on parasitized hosts is high.
Multi-species Assemblages in Biological Control
Competition, resource partitioning, niche overlap, interguild or intraguild predation, and/or emergent properties (e.g. antagonism) can influence pest populations when multiple species of predators and/or parasitoids are present together in an agricultural system. The resulting level of pest suppression as a consequence of these interactions is extremely variable. Multiple natural enemy assemblages can function additively, antagonistically, or synergistically on pest populations. Additive mortality is a situation where two or more natural enemies do not influence each other’s population structure. The resulting mortality on pest populations is equivalent to the sum of mortality induced by the natural enemies independently. Historically, ecologists have considered multiple natural enemies to act additively upon pest populations. However, multiple natural enemy assemblages often display emergent properties (i.e. antagonism or synergism). Antagonism occurs when mortality of a pest population induced by two or more species of natural enemies is less than the additive mortality. Synergism occurs when the combined mortality of a pest population induced by two or more species of natural enemies exceeds the additive mortality from those natural enemies. The level of pest suppression may not be optimized when antagonism among natural enemies occurs. However, synergism can be highly desirable in pest suppression. These associations can significantly influence biological control when multiple species of natural enemies are present.
- To determine the temporal occurrence of P. maculiventris in Northern Florida.
To determine if the occurrence of P. maculiventris overlaps the occurrence of the DBM.
To determine preference of P. maculiventris for unparasitized DBM larvae or larvae parasitized by C. plutellae.
To determine how P. maculiventris and C. plutellae influence P. xylostella populations and plant damage in cabbage.