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Functional Response of Phytoseiulus Persimilis Athias-henriot to Tetranychus Urticae Koch: Effects of Prey Life Stages and Temperature

Md. Fazlul Hoque
Institute of Biological Sciences, University of Rajshahi, Rajshahi

Md. Wahedul Islam
Institute of Biological Sciences, University of Rajshahi, Rajshahi

M. Khalequzzaman
Institute of Biological Sciences, University of Rajshahi, Rajshahi

Abstract/ Executive Summary:

This paper examines the effect of density and temperature on the functional response of adult female Phytoseiulus persimilis to different life stages of the spider mite, Tetranychus urticae. The functional response was determined using functional response assay technique with plant leaf discs an arena. We conducted a logistic regression of the proportion of prey consumed as a function of initial prey density to identify functional response types, and used nonlinear least-squares regression and the random predator equation to estimate attack rates and handling times. In all the cases number of adult male prey attacked by female predator were greater than adult female prey. P. persimilis consumed more eggs and larvae than other stages of prey. Female predator consumed adult prey at each temperature which generally increased with prey density initially but leveled off at higher prey densities. The highest number of eggs, larvae and nymphs consumed by predator in 24 hours was 16.3 ± 0.42, 9.9 ± 0.59 and 9.5 ± 0.40 respectively whereas the highest number of eggs, larvae and nymphs consumed by a single female in 48 hours was 19.5 ± 1.15, 18.6 ± 0.62 and 13.3 ± 0.65 respectively. Handling time generally decreased with temperature whereas successful attack rate increased with temperature except at 30º C. Judging by a/Th values, P. persimilis was most efficient against T. urticae at 30-35ºC, about half as efficient at 25 ºC and performed poorly at 20º C. Again, from a/Th values, P. persimilis was most efficient against T. urticae in egg stage, about half as efficient at larva and nymph stages and performed poorly at adult stage

Keywords: Phytoseiulus persimilis, Tetranychus urticae, functional response, predation

Location: Rajshahi

Start Date:

End Date:

Program Area: Pest Management

Commodity:

Objectives:

This paper presents the results of a set of experiments examining how the predatory efficiency of P. persimilis feeding on different life stages of T. urticae, as measured by a functional response, was influenced by prey density and temperature.

Methodology:

T. urticae colonies were maintained on bean leaf which was cultivated in the experimental fields of the Institute of Biological Sciences, University of Rajshahi. Experimental arenas were constructed by placing excised leaf disk from uninfested bean plants placed on petridish (12 cm diameter) filled with watery cotton bed in the laboratory. The eggs, larvae, nymphs and adult males and females were placed on leaf disks at densities of 10, 20, 30, 40, 50 and 60 per disk. Adult T. urticae were transferred directly to arenas from the colonies on the day of the experiments using a fine point brush. Eggs were obtained by placing T. urticae adults on pest free bean leaves inside a petridish for two days prior to the experiments. On the day of the experiment egg were transferred from the bean leaves inside the petridish to the arenas. Ten replications of each prey density were deployed for the female predator. The arenas were left undisturbed for at least one hour. They were then examined to determine if any eggs had hatched or adults had laid eggs. One P. persimilis was placed at the centre of each of the leaf disks and allowed to feed for eight hours. After eight hours, the number of adult T. urticae and cadavers were counted in the adult and larval arenas, and the number of viable egg were counted in the egg arenas to determine how much prey had been consumed. Temperature was recorded hourly. The number of preys consumed by predators at each density were recorded after 24 and 48 hours respectively from the starting of the experiment. Sets of experiments were repeated at 20°, 25°, 30° and 35°C at prey densities of 10, 20, 30, 40, 50 and 60 maintained in incubators.

Source of Information: Univ. j. zool. Rajshahi. Univ. Vol. 29, 2010 pp. 01-08

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Achievement/Findings:

The predation model estimated in the present study reveals that the expected number of prey attacked similarly. This conclusion is supported by the fractional values of the estimated χ² goodness of fit test, which are much lower than the table χ² value of 11.07 at P<0.05 with 5 degrees of freedom for both life stages and at different temperatures of this predator. This indicates the best fit of the curves. Our results indicate that P. persimilis is highly effective at higher temperatures by significantly increasing its attack rate as well as decreasing its prey handling time. Although the effect of prey density is somewhat limited to generalize it for foraging activity of P. persimilis in our data, it appears to perform well on leaves with some range of prey density. P. persimilis can be a good biological control agent of T. urticae under warm conditions

Knowledge Management: Journal