The effect of the rate of successful dispersal of a phytoseiid mite,Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) on the persistence in the interactive system between the predator and its prey

Dispersal behaviour was studied on a predacious phytoseiid mite, Phytoseiulus persimilisAthias-Henriot in response to the density of its prey, Tetranychus kanzawaiKishida . And the effect of the change in the rate of successful dispersal of the predators among patches was tested on the persistence of the predator-prey system. The results of the study are summarized as follows:

1. With a severe decline in prey density available per individual predator, the predators exhibited a marked behavioural change and dispersed to other areas.
2. When two neighboring host plants did not touch with each other and the dispersal of the predators was possible only through a 20cm plywood “bridge” which connected the two plants, the rate of successful dispersal of the predators was only 20 to 25%, whereas it was 95% when the plants touched with each other.
3. In the system where 32 host plants touched with each other, the predators succeeded in immigrating into all the plants by the 16th day, and they completely eliminated all the prey by the 33rd day.
4. In another system, the 32 plants were equally divided into eight “patches” which were connected with each other with two of the bridges and the predators could move between them only through the bridges as mentioned above. In such a system the predators and their prey coexisted about three times longer than in the other one.
5. It is suggested that for a longer continued coexistence of the predators and prey, it would be necessary to introduce more physical barrier against the dispersal of the predators and to provide more chances for the prey to disperse.

     

The effect of the rate of successful dispersal of a Phytoseiid mite,Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) on the persistence in the interactive system between the predator and its prey

Dispersal behaviour was studied on a predacious phytoseiid mite, Phytoseiulus persimilisAthias-Henriot in response to the density of its prey, Tetranychus kanzawaiKishida . And the effect of the change in the rate of successful dispersal of the predators among patches was tested on the persistence of the predator-prey system. The results of the study are summarized as follows:

1. With a severe decline in prey density available per individual predator, the predators exhibited a marked behavioural change and dispersed to other areas.
2. When two neighboring host plants did not touch with each other and the dispersal of the predators was possible only through a 20cm plywood “bridge” which connected the two plants, the rate of successful dispersal of the predators was only 20 to 25%, whereas it was 95% when the plants touched with each other.
3. In the system where 32 host plants touched with each other, the predators succeeded in immigrating into all the plants by the 16th day, and they completely eliminated all the prey by the 33rd day.
4. In another system, the 32 plants were equally divided into eight “patches” which were connected with each other with two of the bridges and the predators could move between them only through the bridges as mentioned above. In such a system the predators and their prey coexisted about three times longer than in the other one.
5. It is suggested that for a longer continued coexistence of the predators and prey, it would be necessary to introduce more physical barrier against the dispersal of the predators and to provide more chances for the prey to disperse.

     

Functional response,numerical response,and stability in arthropod predator-prey ecosystems involving age structure

Summary A general model of arthropod predator-prey systems incorporating age structure in the predator is employed to study the role of functional and numerical responses on stability and the paradox of enrichment. The destabilizing effect of age structure leads to both qualitatively and quantitatively new results for an environment which has an infinite prey carrying capacity, including a lower bound to prey density for a stable equilibrium, a feature not present in models without age structure. When applied to an environment with finite prey carrying capacity, the effect of age structure is to reinforce the arguments implicit to the paradox of enrichment originally developed for traditional models lacking age structure.     

An experimental study on the foraging behavior of a pit-building antlion larva,Myrmeleon bore

Foraging behavior of a pit-building antlion larva, Myrmeleon boreTjeder was investigated experimentally to elucidate the relation between the feeding level and pit relocation.

1. In artificial sands constructed in the field the 3rd instar larvae of M. bore rarely changed the positions of their pits, though several antlions had moved actively until they constructed pits. The average feeding rate was 0.3 prey/day/pit, and about 60% of prey captured were ants.
2. To examine whether or not M. bore larvae concentrate into the area where they can capture more prey, 8 antlions were released into each of 6 boxes filled with sand. I divided the sand surface of each box into two half areas, then gave prey to the pits built in a half area and gave no prey to the pits built in the other half. During the 50-day observation period, nonfed antlions never moved into the area where prey were given.
3. The 3rd instar larvae were reared separately without food. Even under starved conditions they rarely relocated their pits until dealth. The average duration of survival period was 83.9 days.
4. The experimental results indicate that M. bore larvae adopt a tactic of sedentary ambushing. These larvae exhibit low movement rates which are independent of prey capture rates.

     

Response of predators to prey abundance: separating the effects of prey density and patch size

We tested the relative and combined effects of prey density and patch size on the functional response (number of attacks per unit time and duration of attacks) of a predatory reef fish (Cheilodactylus nigripes (Richardson)) to their invertebrate prey. Fish attacked prey at a greater rate and for longer time in large than small patches of prey, but large patches had naturally greater densities of prey. We isolated the effects of patch size and prey density by reducing the density of prey in larger patches to equal that of small patches; thereby controlling for prey density. We found that the intensity at which fish attacked prey (combination of attack rate and duration) was primarily a response to prey density rather than the size of patch they occupied. However, there was evidence that fish spent more time foraging in larger than smaller patches independent of prey density; presumably because of the greater total number of prey available. These experimental observations suggest that fish can distinguish between different notions of prey abundance in ways that enhance their rate of consumption. Although fish may feed in a density dependent manner, a critical issue is whether their rate of consumption outstrips the rate of increase in prey abundance to cause density dependent mortality of prey.     

A laboratory study on the predatory mite,Typhlodromus pyri (Acarina: Phytoseiidae). II The effect of temperature and prey consumption on the numerical reponse of adult females

The numerical response of adult female T. pyri feeding on different levels of ERM larvae, and at a range of temperatures was examined. The duration of the pre-oviposition period decreased as larval consumption increased, and the rate of oviposition was linearly related to the rate of consumption of larvae. Mathematical models were used to describe these relationships in terms of temperature and consumption of ERM larvae. The results were discussed in relation to the nature of the T. pyri/ERM interaction in New Zealand apple orchards.     

Predation ofApochthonius minimus (Pseudoscorpionida: Chthoniidae) onFolsomia canadida (Collembola: Isotomidae)

Summary We investigated the functional response of the predaceous pseudoscorpion,Apochthonius minimus, to density of the springtail,Folsomia candida, as well as the effects of temperature and prey size on handling time and attack rate. Temperature slightly altered the overall rise in response. Both the rise and shape of the response differed for two prey sizes. The changes in number of prey eaten over a 48-hour period were also examined, and the attack and feeding behaviour ofA. minimus was described and discussed in relation to the predation experiments. The pseudoscorpion preferred young adultF. candida, 0.8–1.2 mm in length, when offered prey in the range, 0.2–1.5 mm.     

The effect of prey size and prey density on the functional response,survival, growth and development of a predatory pentatomid bug,Podisus maculiventris say

Two experiments on the nymphal predation of Podisus maculiventris were conducted using Spodoptera litura larvae as prey. First experiment: The predator nymphs divided into three groups were reared individually from second instar to adult in a small vessel. Each nymph in the groups 1, 2 and 3 was allowed to attack the serially growing larvae (these were supplied at the rate of one per day) from 3-, 5- and 7-day old after hatching, respectively. The first prey used for the group 1 was so small that it was not only insufficient to satiate the predator but also was difficult to be searched out. But these disadvantages were soon recuperated due to the rapid growth of the prey and all nymphs could survive to adults. The survival rate of third and fourth instar nymphs in the group 3 was severely affected by vigorous counterattack of older prey larvae. Second experiment: The predator nymphs were individually reared either in a small vessel or in a large one at various rates of food supply (the prey larvae of 7-day old were used). The functional response curves obtained for each instar of the predator took a saturation type within a certain range of the prey density. The saturation level specific to each instar was generally higher for the predator reared in the large vessel than in the small one. The functional response of fourth and fifth instar nymphs was accelerated at a high prey density, viz. 16 larvae per vessel. Even at the low rate of food supply, viz. one larva per day per predator, the predator nymphs could survive to adults, but the size of resultant adults were abnormally small.     

Predator-prey responses in an acarine system

Summary This study examines the responses of the predatory mite,Phytoseiulus persimilis, to the density and distribution of its prey,Tetranychus urticae. It is divided into three parts. Firstly, the functional responses of protonymph, deutonymph and adult females towards different prey stages are displayed. The great majority of the responses are of the type II form, and the variations in the values of attack ratea′ and handling timeT _h are discussed. Experiments are then described in which individual protonymph, deutonymph and adult female predators are presented with varying ratios of two prey age-classes (eggs and deutonymphs, and larvae and deutonymphs). Any observed preference for one of the prey stages is discussed in relation to the predicted preference on the basis of the separate functional response experiments. Finally, the response of different densities of adult female predators to a non-random distribution of deutonymph prey on bean leaflets is examined. The predators show a clear tendency to aggregate on the leaflets of high prey density, counteracted to some extent by interference increasing the probability of dispersal to other leaflets.     

Biological control of Pacific mites and Willamette mites in San Joaquin Valley vineyards: part III. Role of tydeid mites

In the absence of spider mites, tydeids (Pronematus anconaiBaker and Pronematus ubiquitus [Mc Gregor ]) may serve as alternate prey to maintain good numbers of the predatory mite, Metaseiulus occidentalis (Nesbitt ) (Acarina, Phytoseiidae), late in the season. This late-season predator and alternate prey relationship is necessary to stabilize Pacific mite populations and perpetuate balance in San Joaquin Valley vineyards. Thriving laboratory colonies of tydeids were reared on a diet of windblown pollens, including cattail pollen (Typha sp., Typhaceae) and bottlebrush pollen (Melaleuca sp., Myrtaceae).M. occidentalis was successfully reared on a diet of tydeids and ovipositing predator females were obtained. In addition, pollen dusted on grapevines significantly increased both tydeid and indirectly M. occidentalis populations late in the season. These studies suggest that artificially disseminating cattail pollen or manipulating good pollen producing flora in and around vineyards may be used to correct situations where Pacific mites have become serious pests.     

An analysis of the predator-prey system in the paddy field

A predator-prey system involving Lycosa pseudoannulata as predators and both the green rice leafhopper, Nephotettix cincticeps and the brown planthopper, Nilaparvata lugens as prey was studied in an experimental paddy field. Daily predation rates on the prey and weekly disappearance rates of Lycosa females were related to densities of both predators and prey by multiple regression. During the off-season of reproduction for predators and prey, it proved possible to simulate the interaction between Lycosa and its prey.     

Studies on the basic components of the predation ofPhytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae)

The basic components of the predation of Phytoseiulus persimilisAthias-Henriot feeding upon eggs of Tetranychus urticaeKoch were studied in an open system where the predator could disperse freely. The type of the functional response of the predator to the density of its prey was the same as that studied so far in a closed system, i.e.,Holling's Type 2. The search rate of the predator, however, was much lower in comparison with the result from a closed system. The oviposition of the predator per day was only weakly related to prey densities higher than 10 per leaf disc. But the emigration rate was inversely dependent upon the initial prey density up to 60 per leaf disc. The searching behaviour of the predator was influenced by both the web density spun by T. urticae and the density of the prey: the predator searched for its prey intensively only after it had contact with web. Mutual interference was observed in prey consumption, but not in the emigration rate. The emigration rate was largely dependent upon the prey density available per predator.     

Prey or host searching behavior that leads to a sigmoid functional response in invertebrate predators and parasitoids

Invertebrate predators and parasitoids have long been characterized as having a hyperbolic (Type 2) functional response. Modifications were made to Holling's sand paper disc experiment which consisted of limiting the initial period of search during which a host must be contacted. Failure to contact a host during this initial period causes the predator to emigrate from the search area. The modification generated a sigmoid (Type 3) functional response. This response resulted from the low probability of encountering a host during the initial period of search at low host densities in the time allotted. A limited period of search has been found in several insect parasitoids. Such a strategy would minimize the time (energy) spent per offspring produced by minimizing the time invested in searching microhabitats in which hosts are scarce or absent.