Analysis of Foraging Behavior of the Whitefly ParasitoidEncarsia formosaon a Leaf: A Simulation Study (original) (raw)
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Whitefly, Host Plant and Parasitoid: A Review on Their Interactions
The whitefly, Bemisia tabaci (Gennadius) is an enormously polyphagous insect pest showing the intercrop movement, high reproduction, resistances to insecticides, under-leaf habitat, and virus transmission. In the past decades, numerous studies revealed the interactions of whitefly, host plant, and their natural enemies. The oviposition, development, survivorship, and behavior of B. tabaci are mostly mediated by host plants. Numerous parasitoid species are essential components controlling whiteflies biologically; they parasitize whitefly nymphs and kill them through active feeding. Studies showed that appropriate conservation and augmentation techniques of parasitoids can make them more dynamic on the crops in protected environment and even in exposed cropping field. Moreover, the performance of parasitoid is influenced by several factors including number and release rate of parasitoid, intra- and inter-specific competition, stage, size and density of whitefly nymph as well as environmental factors and host plants. In this review, we summarized the progress and findings of how B. tabaci adapt on various plant species, interactions of host plant and the whitefly, B. tabaci, interactions between parasitoids and plant species, interactions among parasitoid species, interactions among host plant, B. tabaci and parasitoid in the last decade. We also discussed the possibility of using parasitoids for suppression of whitefly populations.
Biological Control, 1997
Biological control strategies of greenhouse whitefly with the parasitoid Encarsia formosa were studied with a simulation model of the parasitoid-host interaction in a crop. The model is based on developmental biology of both insect species and on the searching and parasitization behavior of individual parasitoids, in relationship to host plant characteristics and greenhouse climate. The model includes stochasticity and a spatial structure which is based on location coordinates of plants and leaves. The simulated population increase of greenhouse whitefly in the absence or presence of parasitoids agreed well with observed populations in a tomato crop. Whiteflies were suppressed rather than regulated by the parasitoids at extremely low densities (F0.3 unparasitized pupae per plant), but did not become extinct. The percentage of black pupae fluctuated between 40 and 70%. According to the model, the parasitoid adults reached high densities of 7.4 per plant, but due to the low whitefly density not more than 1% of the parasitoids were searching on infested leaflets. The degree of whitefly control was strongly affected by variation in giving up time (GUT) of the parasitoids. When variation in GUT was excluded in the model, the whitefly population became almost extinct. Other important parameters of the parasitoid which strongly influenced the level of control were the walking speed and walking activity, the probability of oviposition after encountering a host, the ratio of search times on both leaf sides, and the longevity. The combined effect of these important attributes of a parasitoid can be tested with the model. When comparing successes of E. formosa on different crops, attention should be focused on the same parameters plus the whitefly development duration and the number, size, and production of leaves in the canopy. The model can be used to evaluate a number of release strategies on several crops and under various greenhouse climate conditions. r 1997 Academic Press KEY WORDS: Trialeurodes vaporariorum; Encarsia formosa; parasitoid-host interaction; population dynamics; biological control; individual-based simulation model; spatial heterogeneity.
Pest management science, 2017
Mechanisms behind the success and failure of whitefly biological control using parasitoids are largely unknown. Here we use the Eretmocerus warrae-greenhouse whitefly system to investigate how fluctuating density of the parasitoid and its host affects three key parasitoid fitness parameters: host searching, host feeding and parasitization, providing critical knowledge for evaluation and development of whitefly biological control programs. This is the first such study in a parasitoid-whitefly system. Models used and developed here show that (1) both host feeding and parasitism fit a Type II functional response; (2) overall parasitoid-caused whitefly mortality significantly increases with growing density of both organisms and the parasitoid density has significantly more positive effect; (3) with the pro-synovigenic nature, E. warrae allocate significantly more resources to parasitization than to host feeding activity in low whitefly density and high parasitoid density, and (4) low mu...
Bulletin of Insectology, 2009
The present work contributes to an accurate quantification method of the parameters of the biotic potential of Encarsia formosa Gahan (Hymenoptera Aphelinidae), applicable to other species of whitefly parasitoids. The oviposition devices are easy to make and they allow standardisation of a whitefly parasitoid study by daily observations of the main parameters such as fecundity, longevity and host-feeding by adult parasitoids, which are important for the parasitoids mass-production and biological control of whiteflies. Results show that two physical parameters determine the expression of biotic potential: the confinement induces an important decrease of the fecundity and longevity of E. formosa; the position of plant leaf with nymphs of Trialeurodes vaporariorum (Westwood) (Homoptera Aleyrodidae) that the parasitoid female can explore for oviposition and host-feeding influences on the biotic potential. The heterogeneity observed in the replicates suggests that during their mass-proce...
Oikos, 2004
We developed a dynamic state variable model for studying optimal host-handling strategies in the whitefly parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae). We assumed that (a) the function of host feeding is to gain nutrients that can be matured into eggs, (b) oögenesis is continuous and egg load dependent, (c) parasitoid survival is exponentially distributed and (d) parasitoids encounter hosts randomly, are autogenous and have unlimited access to non-host food sources to obtain energy for maintenance and activity. The most important prediction of the model is that host feeding is maladaptive under field conditions of low host density (0.015 cm (2) and short parasitoid life expectancy (maximum reproductive period of 7 days). Nutrients from the immature stage that can be matured into eggs are sufficient to prevent egg limitation. Both host density and parasitoid life expectancy have a positive effect on the optimal host-feeding ratio. Parasitoids that make random decisions gain on average only 35% (0.015 hosts cm (2) to 60% (1.5 hosts cm (2) of the lifetime reproductive success of parasitoids that make optimal decisions, independent of their life expectancy. Parameters that have a large impact on lifetime reproductive success and therefore drive natural selection are parasitoid life expectancy and the survival probability of deposited eggs (independent of host density), the number of host encounters per day (when host density is low) and the egg maturation rate and number of host types (when host density is high). Explaining the evolution of host-feeding behaviour under field conditions requires field data showing that life expectancy in the field is not as short as we assumed, or may require incorporation of variation in host density. Incorporating variation in walking speed, parasitised host types or egg resorption is not expected to provide an explanation for the evolution of host-feeding behaviour under field conditions.
Increase of Whitefly Parasitoids: Design of an Oviposition Device
2014
The present work contributes to an accurate quantification method of the parameters of the biotic potential of Encarsia formosa Gahan (Hymenoptera Aphelinidae), applicable to other species of whitefly parasitoids. The oviposition devices are easy to make and they allow standardisation of a whitefly parasitoid study by daily observations of the main parameters such as fecundity, lon-gevity and host-feeding by adult parasitoids, which are important for the parasitoids mass-production and biological control of whiteflies. Results show that two physical parameters determine the expression of biotic potential: the confinement induces an important decrease of the fecundity and longevity of E. formosa; the position of plant leaf with nymphs of Trialeurodes vaporari-orum (Westwood) (Homoptera Aleyrodidae) that the parasitoid female can explore for oviposition and host-feeding influences on the biotic potential. The heterogeneity observed in the replicates suggests that during their mass-pro...