Structure and Function in Agroecosystem Design and Management - Chapter 8 ppt

167 Nature of Species Structure and Abundance of Predacious Phytoseiid Mites.. This chapter focuses on the species structure and abundance of predacious mites of the family Phytoseiidae

CHAPTER 8

Species Structure and Abundance

of Invertebrate Natural Enemies in

Sustainable Agroecosystems Hiroshi Amano

CONTENTS

Introduction 167

Nature of Species Structure and Abundance of Predacious Phytoseiid Mites 170

Geographical and Climatic Factor 170

Food Habits and Co-occurring Prey Species 171

Physical and Chemical Factors of Host Plant 171

General Pattern of Dominancy in Phytoseiid Fauna 173

Attributes of Mite Species Commonly Found in Agroecosystems and Factors Affecting their Abundance 175

Phytoseiid Fauna in North American Apple Orchards 176

Pesticide Application as Ultimate and Proximate Factors 178

Cultural Practice as Ultimate and Proximate Factors 179

Change in Prey Fauna as a Proximate Factor 179

Competitive Interaction as an Ultimate Factor 180

Use of Natural Enemies in Sustainable Agroecosystems as Concluding Remarks 181

References 181

INTRODUCTION

Recent expansion of the integrated pest management (IPM) system has revolutionized the whole concept of crop protection not only in Japan but

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Table 8.1 Major Natural Enemies of Spider Mites in Agroecosystems of

Japan

Insecta

Oligota yasumatsui

Orius nagaii Orius sauteri

Arachnida

Amblyseius eharai Amblyseius womersleyi Typhlodromus vulgaris

others

Agistemus terminalis

also in other areas of the world Consequently, applied entomologists and fundamental ecologists enjoy unexpected favor at all levels, not only to boost crop yield but also to preserve nature For a long time, the nature of biotic interactions has been undiscovered and hidden in agricultural lands by heavy use of agrochemicals Japan, one of the leading producers of these chemicals, unfortunately has taken the lead in throwing them into various facets of agroecosystems, where a rich biotic fauna of the temperate zone was originally established

A unique problematic example showing this process is a fauna of natural enemies of notorious pest mites It is a well-known fact that spider mites were not of primary importance in pest management prior to the intensive intro-duction of synthetic agrochemicals in the 1960s Mites had been well under control by a complex of natural enemies, paradoxically proven by many observations in which cessation of using pesticides and acaricides quickly recovered natural enemies resulting in suppression of the mite population at low levels Due to persistent use of many chemicals, however, potential nat-ural enemy fauna, especially in the 1960s and 1970s, was undiscovered com-pletely, and it remained obscured until today An overall picture of natural enemy fauna for spider mites is composed of predacious insects and mites (Table 8.1) These two taxa often co-occur in the field and together play an important role in depressing prey population Although there are some dif-ferences in their predacious and habitat characteristics (Table 8.2), both groups share a common weakness against most agrochemicals Under these circumstances, few long-tem studies on their dynamics in sustainable as well

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as conventional agroecosystems are available, and analysis of factors respon-sible for their abundance is lacking

With the increasing emphasis on biological control as a core component

in IPM, there is an urgent need to understand biocontrol agents with respect

to the prevailing agroecosystem This chapter focuses on the species structure and abundance of predacious mites of the family Phytoseiidae in Japan, fol-lowed by investigation into possible factors that determine their existence in the field Given results and hypotheses may be helpful in understanding and predicting the behavior of natural enemies in upcoming sustainable agro-ecosystems

NATURE OF SPECIES STRUCTURE AND ABUNDANCE OF

PREDACIOUS PHYTOSEIID MITES

As mentioned briefly in the previous section, members of the family Phytoseiidae show a remarkable ability to depress spider mite population by their good numerical response and high stability in prey colony Their body size (about 0.4 mm for the largest adult female) is as small as prey mites, but they are able to attack all stages of spider mites, although details of their bio-logical attributes are species-specific (e.g., McMurtry et al., 1970) About 1600 species are known to occur in the world (Chant and McMurtry, 1994) Recently, Ehara and Amano (1998) reviewed Japanese phytoseiid fauna and nominated, in total, 77 species with short remarks on their biology They also categorized phytoseiid fauna into several groups after a close investigation of their association with different food habits and habitat In reference to the basic picture presented by these authors, factors that may influence phyto-seiid distribution and survival, especially in natural ecosystems, are described in the following section Certainly, these factors act simultaneously

in the field, but for clarification are explained separately below

Geographical and Climatic Factor

The climatic conditions in Japan are somewhat hostile for the establish-ment of beneficial phytoseiid species of tropical or subtropical origin, which

include members in the genus Phytoseiulus Moreover, no Galendromus and

Metaseiulus species have been found These two genera are of major taxa in

the subfamily Typhlodrominae in the New World (Chant and McMurtry, 1994; Ehara and Amano, 1998) Looking at domestic phytoseiids, two species

with similar ecological niches show contradictory distribution: Amblyseius

finlandicus is well distributed in northern or elevated areas of Japan, whereas

A sojaensis is normally found in southern Japan Some geographical and

associated climatic conditions must have played an important role in their survival and establishment, and species seen in agroecosystems are not exceptional in this matter

Food Habits and Co-occurring Prey Species

No species have exactly the same food requirement and prey preference, and thus it is understandable that prey availability and distribution may determine establishment of predacious mites Even on the same host plant, different fauna of phytoseiid mites will become dominant if prey species are changed with some reasons One of the important factors in this regard is webbings produced by spider mites Heavy web structures constructed by

Tetranychus spp., in particular, easily eliminate certain phytoseiid species

from the field, and often simplified their fauna (discussed in later sections) Table 8.3 shows a general scheme of four phytoseiid genera adapting to dif-ferent food types It seems that there is a trend of increasing dependability on

animal food along the genus line of

Phytoseius-Typhlodromus-Amblyseius-Phytoseiulus Of course, exceptional species can be found among various

genus In agroecosystems, abrupt turnover of prey species complex is often caused by human manipulations such as spray application

Physical and Chemical Factors of Host Plant

The use of the term host plant for natural enemies is misleading because

it is not purely phytophagous, but, for convenience, this word is used throughout this chapter for the plant on which the mites are collected The physical structure on plant surfaces unexpectedly influences the successful colonization of phytoseiid mites Leaf structure may includes roughness, pubescence, vein structure, domatium, and others (e.g., Collyer, 1976; Walter and O’Dowd, 1992) It is also suggested that volatile chemicals of host plants sometimes play a key role in the trophic triangle of host plant-prey mite-predacious mite (e.g., Dicke et al., 1990)

Physical and chemical factors of host plants may also affect food prefer-ence and colonization of spider mites, and thus it is sometimes difficult to identify the ultimate reasons, between changes in prey species and host plants, for turnover of phytoseiid fauna Nevertheless, Table 8.4 summarizes dominant phytoseiid species, which attack the population of a spider mite,

Tetranychus kanzawai, in Japan for each host plant separately Among these

plants, basic fauna of predators is similar, but the predominant species on each plant (shown in the order of their abundance in the table) show some

differences For example, A womersleyi commonly dominates on tea and Kudzu vine, but it is replaced by A eharai on hydrangea and Glory-Bower.

Distribution of predacious mites shows subtle differences even on the same tree In 1988, mites were collected throughout seasons from water sprouts of Japanese pear trees in a small experimental orchard, and species were identified (Table 8.5) Due to unsprayed conditions for more than 10

years, a rust mite, Eriophyes chibaensis, is the only prey source for predators on

both leaves and twigs of the sprouts These phytoseiid species lived under the same climatic conditions and associated with the same prey, but they

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showed some discrepancies in species abundance between leaves and twigs

on the same sprouts It was assumed at least that certain plant morphology and physiology might have affected microhabitat selection of each species in the field

General Pattern of Dominancy in Phytoseiid Fauna

Is there any general pattern in phytoseiid fauna under relatively undis-turbed environments? This question is a topic in the present section and includes information useful when sustainable agroecosystems are once established In Table 8.6, species structures of phytoseiid mites are shown as percentages for several natural or seminatural ecosystems Three dominant species on each host plant occupied 67 to 99% of all specimens, and in two cases two dominant species accounted for over 90% (Kudzu vine and cherry

in Matsudo) These values suggest that in undisturbed conditions, two or three species co-occupy the habitat and share resources in the single season

Table 8.4 Dominant Phytoseiid Species in Japan Attacking Tetranychus

kanzawai on Different Host Plants

Host Plant Phytoseiid Species

Species are arranged in the order of their abundance.

Table 8.5 Species Structure and Abundance of Phytoseiid Mites on Water

Sprouts of Nonsprayed Japanese Pear Trees Species (no of adult females and % in parentheses)

On Leaves (n  145) On Twigs (n  41)

Surveys were conducted on 20 sampling dates in 1988 in an unsprayed small experimental orchard in Chiba Prefecture, central Japan Predacious mites on different parts of water sprouts were separately collected and identified.

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In other words, this pattern could be an attribute that belongs to the phyto-seiid community in common

The species structure and abundance shown in Table 8.6 calculations were based on all specimens collected on the host plants during the survey season, and, thus, in some cases a seasonal discrepancy in abundance did not appear The dominant phytoseiid species was dramatically changed on

cherry in spite of year-round occurrence of the prey mite Tet viennensis

(Figure 8.1) Factors responsible for this seasonal change are not fully under-stood, and therefore further investigation is necessary

ATTRIBUTES OF MITE SPECIES COMMONLY FOUND IN AGROECOSYSTEMS AND FACTORS AFFECTING THEIR

ABUNDANCE

Among 77 species recorded from Japan (Ehara and Amano, 1998), 14 species are relatively common in a variety of agroecosystems (Table 8.7) Under the present pest management system, chemical control dominates other tactics of crop protection Phytoseiid species, which successfully sur-vive in such conditions, have some potential of pesticide tolerance

Furthermore, pest mites of the genera Tetranychus and Panonychus usually

increase their numbers by resurgence, and thus predators in close relation to

Figure 8.1 Seasonal population dynamics of two dominant phytoseiid species on

cherry trees in Matsudo, Chiba, Japan in 1994 They were closely

asso-ciated with a prey mite, Tetranychus viennensis.

these prey may have advantages As pointed out earlier, ability of phytoseiid species to be generous with spider mite webbing is a precious talent to increase their population in available prey resources, especially against

genus Tetranychus All species of Phytoseius and Typhlodromus and many species of Amblyseius listed in Table 8.7 lack at least one of these abilities.

Japan, extending north to south, is a country with extreme variations in climate, and climatic conditions in the northern area are supposed to be severe for the survival of most species Cold tolerance and overwintering

ability are important characteristics for species survival as shown for A

wom-ersleyi by Kishimoto and Takafuji (1994 and 1997) They showed that

popula-tions from the north had higher diapausing capacity than the southern population but at the expense of a narrower temperature range in which they could display their full reproductive ability In the following section, details

of factors that affect the abundance of phtyoseiid mites in agroecosystems are described

Phytoseiid Fauna in North American Apple Orchards

Surveys on apple trees in the “apple belt” of North America are by far the most complete among any studies for phytoseiid fauna on a single host plant Those from the 1960s and 1970s are especially useful because few exotic species were experimentally introduced into the areas in those eras Table 8.8 shows dominant species in the eastern, central, and western regions of the apple belt for sprayed and unsprayed orchards separately In commercial

sprayed orchards, A fallacis predominated in 14 states and provinces of

east-ern and central regions, whereas in five westeast-ern states and provinces

Typhlodromus occidentalis predominated.

When crop protection practices including sprays were discontinued, more species were observed in the orchards, and this trend was common in all apple

orchard regions of North America In the eastern to central regions, T pomi became most abundant and widely distributed Phytoseius macropilis seems to have a second position in this context In the west, however, T caudiglans and

T pyri (in British Columbia) or T flumenis (in Utah), for example, dominated

in the orchards, and T pomi was never as numerous as in other regions.

Table 8.7 Phytoseiid Species Commonly Found in Japanese Agroecosystems Genus No of Species Species Name

koyamanus, makuwa, okinawanus, orientalis, sojaensis, tsugawai, womersleyi

Species were collected from agricultural crops and/or groundcovers.

Based on the results shown here and other studies, a generalized dia-gram showing overall relationships of factors that possibly change phyto-seiid fauna in agroecosystems is described in Figure 8.2 For simplicity, any changes originating from climatic factors were excluded from the diagram Three factors are assumed as major components of the ultimate factor: pesti-cide application, cultural practice, and competitive interaction between species In the figure, a proximate factor is also inserted: change in prey fauna Pesticide application certainly operates as the most influential factor

in the field either directly (killing predators) or indirectly (killing certain prey species) Cultural practice of crops, such as weed management, also deter-mines abundance of predators directly or indirectly In contrast, competi-tive interaction among predators is not well understood, but it is probably

Table 8.8 Dominant Phytoseiid Species in North American Apple Orchards Regions Commercial (sprayed) Unsprayed or Abandoned

Typhlodromus longipilus Amblyseius finlandicus

Phytoseius macropilis Typhlodromus caudiglans Typhlodromus citri Amblyseius andersoni

After Amano (1985).

Species are arranged in the order of their abundance.

Figure 8.2 Diagrammatic representation showing factors responsible for change in

phytoseiid fauna in the field.