G. I. Vasechko stability of terrestrial ecosystems to plant pests: an axiomatic approach. Part II. Substantiation of the axioms proposed in the part I




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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.

PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I

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AXIOM 8(1) FACTORS of DISTURBANCE of ECOSYSTEM STABILITY
to PLANT PESTS and their EFFECTS

To keep ESPPs in any ecosystem on the admissible level as long as possible, it should know the factors, which disturb it. A meaning of the term "disturbance" needs in some sidelight. It should pay attention on the difference between life strategy of biocenoses and destination of articenoses.

The life strategy of biocenoses is directed on keeping ESPPs biomass of the category D I on the level 3.1. "Proper control." The decrease ESPPs in this category of biomass under diverse stressors to the level 3.2. "Lag control" endangers biocenoses by a change of composition of dominants. The decrease ESPPs of it on the level 3.3."Late control" results in destruction of biocenoses.

Contrary, on the biomass of the category D II, a decrease ESPPs on the levels 3.2. and 3.3. has no a destructive character. In some environmental conditions, it takes place an often decrease ESPPs to the level 3.3. "Late control." The advanced Tolerance of dominants allows biocenoses to survive in spite of the common affection by herbivores. It is necessary, however, a periodic suppression of herbivores by CESPPs 2.5. "Effects of crowding", which provides a reprieve for restoring of vitality of dominants. Therefore, on biomass of the category D I, a disturbance changes a character of an ecosystem, and it is undesirable, whereas on biomass of the category D II due to advanced Tolerance the term a "disturbance" has no obligatory a negative sense.

The destination of articenoses, which is determined by people, is directed on keeping the level ESPPs 3.1. "Proper control" both in biomass of the categories D I and D II. When signs of a decrease of ESPPs from the level ESPPs 3.1. "Proper control" appear, CESPPs 2.6. "Human control measures" usually need to be entered in an operation. This is necessary in agricultural crops, where decrease of yielding and keeping of quality of production are the main concern of ecosystems. In ecosystems of other concern, the need of application CESPPs 2.6. "Human control measures" depends on local circumstances.

All the stressors, which decrease ESPPs from the level 3.1. "Proper control", will be referred to as factors disturbing ecosystem stability to plant pests (FDESPPs). Further, it will be considered the conditions, at which diverse FDESPPs are active, and their effects on dominants will be shown.

It has been declared the skepticism as to the durability (persistence) of plant resistance to PPs, which is implied as Antibiosis, due to arising of new pathotypes of phytopathogens and new biotypes of herbivores, which would capable to overcome the resistance.

Indeed, frequency of hereditary changes in PPs is much greater than that in their host-plants. The microevolutionary process that leads to a lost of the resistance in the system of interrelations " a host-plant - a consumer" has been considered by D. Pimental (1961 and other publications), and has got the special term the "genetic feed-back mechanism." Beside the mathematical proof, D. Pimental has given a number of examples, which illustrate the action of this mechanism in nature. It is known a row of cases, at which plant cultivars loss their resistance to PPs in innumerous years after wide-scale growing of these cultivars as field crops.

However, a lot of facts demonstrate the presence of an opposite trend. In this connection, it should mention the words by R.L. Gallun and G.S. Khush (1980, pp. 82 83), namely: "The breakdown of resistance may occur after few years although in some cultivars resistance remains for the last 50 years."

Consider prospects of keeping of plant resistance to PPs taking into account of FDESPPs and the circumstances, at which they are active, as well as the ways to counteract losses of the resistance.


8.1. Anthropic-1

8.1.1. Growing of cultivars in the range of exotic herbivores r-strategists

Breakage of the prerequisites:

2.1.1.P.1. A hereditary ability of a plant taxon (species, subspecies, phenological forms, varieties strains, hybrids, lines) to resist against a given taxon of PPs

2.2.1.P.2. Adaptation of parasites and pathogens to overcome resistance of their hosts

2.2.1.P.9. Presence of effective vectors of pathogens

8.1.1.1. CESPPs A.2.1.1.2.1. , 2.2.1., and 2.2.3. failed

8.1.1.1.1. Repeated arising of aggressive biotypes inducing outbreaks of the herbivores

As examples of this category, it can be used the cases offered by M.D. Pathak (1970). This is a list of pest insects, including the Hessian fly, Mayetiola destructor and five species of aphids, which overcome Antibiosis of their host-plants repeatedly by producing aggressive biotypes. They are the raspberry aphid, Amphoraphora rubi, the spotted alfalfa aphid, Theriophis maculata, the greenbug, Schizaphis graminum, the corn leaf aphid, Rhopalosiphum maidis, and the pea aphid, Acyrthosiphon pisum.

All the above species are r-strategists. The fly produces up to five generations per season, whereas the aphids have to ten ones or even more. The more number of generations of a herbivore per year, the more hereditary changes in its population, the more probability of arising of mutants with genes, which are able to overcome host-plant Antibiosis, rather that Antibiosis in host-plants to the above herbivores is not well-developed, if any.

These species feed on plant’s parts, which related to biomass of the category D- II. In native lands of the herbivores, these parts are protected by CESPPs A.2.1.1.3.1.2. "Tolerance to herbivores, Repair or compensation of losses of host-plant tissues" in cooperation with CESPPs 2.2.1. "Natural enemies of invertebrate herbivores", A.2.1.2.1.1. "Superevasion from herbivores." or 2.1.1.4.1. "Evasion from herbivores." Being exotic species in North America, they hardly to suffer seriously on the part of natural enemies. At such circumstances, Tolerance is insufficient for self-protection of host-plants. If breeding of varieties having Antibiosis to the herbivores was conducted, the Antibiosis, however, occurred to be not potent, when to take into account specificity of tissues under the affection - young tillers, juvenile parts of stems, and foliage. There are the grounds, therefore, to consider the hereditary prerequisites of CESPPs Antibiosis in the given case as failed ones. In literature, such Antibiosis is characterized as monogenic one or the vertical resistance.

A combination of the above factors: advanced capacity of the herbivores - r-strategists to produce aggressive biotypes, low activity, if any, of resident natural enemies of these exotic herbivores, and weak expression of CESPPs A.2.1.1.2.1. "Antibiosis to herbivores" in the crops results in the loss of Antibiosis. Hereditary prerequisites of this Antibiosis in the above conditions failed.

In this context, it should paid attention that in exotic herbivores K-strategists, an arising of aggressive biotypes has not been traced. This fact was reported again by M.D. Pathnak (1970), in particular, in the wheat stem sawfly, Cephus cinctus and the European corn borer, Ostrinia nubilalis. Further, the plant’s parts, which are affected by these species, might by provided more developed Antibiosis than that in the above herbivore r-strategists. So that, hereditary prerequisites of CESPPs A.2.1.1.2.1. "Antibiosis to herbivores" in the K-strategists are rather durable ones.

Consider the ways to withstand an activity of FDESPPs 8.1.1. "Growing of cultivars in the range of exotic herbivores r-strategists." These ways are practicing of CESPPs A.2.1.2.1.1. "Superevasion from herbivores", A.2.1.1.3.1.2. "Tolerance to herbivores, Repair or compensation of losses of host-plant tissues", and 2.2.1. "Natural enemies of invertebrate herbivores" by means of introducing of them.

The Hessian fly is known in North America from XVIII century, and it continues to be a serious pest mainly of the spring wheat until now. It has been bred a number of cultivars with Antibiosis to this pest, but duration of efficacy of this trait is limited due to arising of aggressive biotypes of the pest. The author has not found in literature reports about introducing of natural enemies of the Hessian fly. Probably, such attempts were been conducted, but they were not insistent.

The aggressiveness of the Hessian fly in America is more expressed than that in Europe. That fact might be explained by difference in activity of natural enemies of the Hessian fly in the compared continents.

Considering of the well-documented situation with the Hessian fly in Russia is able to bring clearness in the issue. This pest probably invaded in this country in the middle of XIX century or its aggressiveness was a result of mutation of a native species, as A.F. Kryshtal (1950) supposed. Over nearly a century, it was very dangerous, when its outbreaks arose with short intervals.

The first outbreak was recorded in Russia in 1847. Since the outbreaks were reported to be in 1879 1885, 1890, 1896 1898, 1906 1908, 1911 1913, 1923 1925, 1937 1938, 1948 1955, 1961 1963 (Pavlov, 1967, pp. 47 48). The level of affection becomes clear from the report by A.Ph. Kryshtal (1947, p. 12). According to this scholar, in 1938, the fly's outbreak was the most sever over 40 50 preceding years. On 1,621,731 hectares of the surveyed area in Ukraine, density of the fly (the number of larvae or pupae per square meter of the soil surface) reached in the spring wheat 300 individuals on 34.8% of the area and 1000 individuals on 8.6% of the area. In the winter wheat, the affection with the rate over 300 individuals was on 12.8% of the crop's area

Eventually, in USSR, the damage due to the Hessian fly has become less. After 1960-ies, outbreaks of the Hessian fly were recorded and forecasted in 1979 1980, 1991 1992 and in 2000 2001 (Biletsky, 1994). However, any general increase of density of this species in 1987 2001 in Ukraine was not recorded (G.A. Posylayeva, pers. comm. and author's observations). Over last decades, in the Forest-Steppe biome in Ukraine, it is known only one case of significant damage due to this species, namely: in 1972 several hectares of the winter wheat were damaged seriously by the fly in a breeding center (L.A. Burdenyuk, pers. comm.).

Even in the Steppe zone, where activity of the fly is usually more expressed, it has not been recorded over 1990-ies the decrease of grain yield in the winter wheat at the highest of the revealed values of the density - affection of 46% of tillers in fall and presence of cocoons in 14% in sheaths of stems in summer (Krut, 1992; 1998, pp. 51 52).

In the past, aggressiveness of the Hessian fly in the Steppe zone was higher. This problem was studied by P.I. Susidko (1969), who reported the following terms of Hessian fly outbreaks in the south of Ukraine (Ibid., pp. 19, 27): 1881, 1884 1885, 1890, 1892, 1896 1897, 1907 1908, 1910 1911, 1922 1924, 1930 1932, 1937 1938, 1947 1948, 1951 1952, 1959, 1966. In 1959, on irrigated wheat fields, the density of the Hessian fly exceeded 1000 larvae per square meter of the soil surface, so that one affected stem contained in average more than three larvae (Ibid.).

This species has developed SP – up to five generations per year that allows it to give a quick rise of density.

P.I. Susidko (1969, p. 19) stressed that outbreaks of the Hessian fly did not demonstrate any periodicity. Its High density continued one-two years. Since then, it took place a depression, which continued from one to ten years.

This view contradicts one keeping by Eu.S. Biletsky (1994), who attempts to connect arising of Hessian fly outbreaks with the periodicity of the solar activity.

As a cause of fluctuation of fly’s density, it might be diversity of weather situations. The role of weather has been stressed by A.F. Kryshtal (1972, pp. 504 506). He has noted that sharp change weather situation in spring from cold to continual warm one promotes to growth of the density. Contrary, a return of cold weather in spring after short warm weather induces mortality of the neonate larvae. The stable wet weather during summer does not promote an increase of the density, because the flies are active, but they unable find host-plants in the vulnerable stage – with young tillers, which are absent. On the other hand, at droughty summer, the flies stay in diapause. In fall, they become active and find abundant young tillers on winter wheat fields. In addition, wet weather over summer promotes activity of chalcidid parasites of the Hessian fly, whereas droughty summer suppresses them (Rubtsov, 1938).

As an explanation of the trend to decrease of aggressiveness of the Hessian fly, it can be proposed an adaptation of resident natural enemies to use this species as a host. For substantiation of this proposition, it can serve the data offered by A.V. Znamensky (1926, p. 213). These data allow comparing mortality of a fall generation of the Hessian fly in Poltava (Ukraine) in 1923 at the early sowing date, and in Lafayette, Ind. (USA). The observations in Lafayette were conducted between September 11 and October 16, 1921. As to Poltava, the data are obviously original ones by A.V. Znamensky. A source of the data for Lafayette was not noted. In the Table 38, it is shown the comparative mortality of a fall generation of the Hessian fly in the stages of egg, larva, and pupa.

Table 38. The comparative mortality of the Hessian fly in Poltava (Ukraine) in 1923, and in Lafayette, Ind. (USA) in 1921



Location

Crop

The number of studied objects

Percentage of plantlets with eggs

Percentage of objects with larvae and pupae

The number of eggs per plantlet

The overall number of eggs

The overall number of larvae and pupae

Survivorship, percentage

Plantlets

Tillers

The number of tillers per plantlet

Plantlets

Tillers

1

2

3

4

5

6

7

8

9

10

11

12

Poltava

The winter wheat

212

1695

8

100

44

52

56

11872

28

0.23

The winter rye

189

1701

9

87

7

6

19

3116

7

0.22

Lafayette

The winter wheat

50

135

2.7

100

69

44

36

1796

284

15.8

The winter rye

50

410

8

90

6

0.7

12

580

7

1.3

The Table 38 demonstrates the great difference in survivorship of the Hessian fly between the areas. In Lafayette, Ind. (USA), the survivorship was much higher than that in Poltava (Ukraine). The difference can be due to the better adaptation of natural enemies (probably parasites and pathogens) to this insect host in Poltava comparing with that in Lafayette.

Why does the activity of natural enemies of the Hessian fly in Poltava is greater than that in Lafayette? The answer is the rich fauna of relatives of the Hessian fly in Ukraine. In Europe, including Ukraine, it was recorded a number of species of the genus Mayetiola: M. avenae March., Mdactylidis Kieff., Mdestructor Say, M. joannisi Kieff., Mschoberi Barnes, and M. poae Bosc. (Mamayeva and Mamayev, 1981).

In Ukraine, on the Hessian fly, it has been recorded twenty species of parasites (Bilanovs’ky, 1940, cited in A.F. Kryshtal, 1974, p. 505). From them, the most numerous are Eupteromalus micropterus, Merisus destructor, Platigaster minutula, and Eupelmella vesicularis.

As an example of potency of the parasites, it can serve the wasp Platygaster minutula Lind., Proctotrupidae, which oviposites in eggs of the Hessian fly, and the progeny finishes development in larvae or pupae; due to polyembriony, 15 20 larvae of the parasite develop from one of its egg (Shchegolev et al., 1949, p. 389).

An activity of the parasites is high in vicinity of forest plots and shelterbelts (Kryshtal, 1974, p. 505).

In wild vegetation, important role in SES is played by CESPPs 2.1.1.4.1. "Evasion from herbivores" operating on the level of separate plants. In crops, it is very effective of CESPPs A.2.1.2.1.1. "Superevasion from herbivores." Sowing of winter wheat in the optimal dates, which have been determined for diversity of States, prevents exposition of plants in vulnerable stage on the flies (Fernald, 1926, p. 316).

The Superevasion is prospective concerning the spring wheat. In fact, "In the spring-wheat section late seeding will not apply. It seems likely, on the contrary, that the earlier it is sown in spring the less it will suffer from the Hessian fly" (Fernald, 1926, p. 317).

The trait A.2.1.1.3.1.2. ''Tolerance to herbivores, Repair or compensation of losses of host-plant tissues'' allows the crops to survive in spite of significant activity of the Hessian fly.

Turning to the Table 38, it is noticable high general tillering of the crops – eight tillers in the winter wheat and nine tillers in the winter rye. Abundant tillering allows to plants to tolerate losses of their tillers due to affection by the fly in fall, and to restore tillers in spring. To overwinter succesfully, a plant needs in only two tillers.

Nevertheless, CESPPs A.2.1.2.1.1. "Superevasion from herbivores" is insufficient for reliable protection of the spring wheat and in the winter wheat on condition that it grows in southern areas, where the fly can be active over winter. In such a situation, it is need cultivation of the varieties possessing the trait of expressed Antibiosis to the Hessian fly.

The Antibiosis is prospective, particularly in North Kazakhstan. Here, Mayetiola destructor is a tiresome pest (Yevdokimov et al., 1986). In these climatic conditions, it is possible to grow only the spring wheat, so that Superevasion is insufficient for the protection. Arid climate does not promote abundant general tillering, so that Tolerance is also insufficient. Further, areas of natural woody ecosystems and shelterbelts, where pest's parasites and predators find favorable conditions for overwintering and additional (imaginal) feeding, are actually absent. At last, here it is practiced the soil treatments without digging up. In this area, it is necessary the surface tillage - sharing for protection of the soil from wind erosion. That is why the fly overwinters successfully into shready stalks, whereas the wheat is grown as a monoculture.

At growing of wheat cultivars with Antibiosis to the Hessian fly, recurrence of outbreaks takes place at arising of aggressive biotypes of the pest. Contrary, growing of the winter wheat in the conditions, where Superevasion is effective, Tolerance is developed, and natural enemies of the fly are prosperous, results in unlimited keeping of its density on the Insignificant level.

Population dynamics of the exotic species of aphids is similar to that of the Hessian fly. This suggesion is concerned to the above-cited species Amphoraphora rubi on the raspberry, Theriophis maculata on the alfalfa, Schizaphis graminum on the wheat and the sorgum, Rhopalosiphum maidis on the sorgum and the corn, and Acyrthosiphon pisum on the pea, rather that Antibiosis against them is not expressed well. In their EEs in the native land, the role of Tolerance and activity of natural enemies is supposedly great one, so that there is no need in developed Antibiosis. A cooperation of all the above CESPPs provides admissible suppression of their density. Contrary, in the recently invaded area, low activity of natural enemies results in rather soon loss of Antibiosis. On the other hand, Tolerance is insufficient for self-protection in the conditions of high activity of herbivores – r-strategists.

Causes of outbreaks of the Russian wheat aphid, Diuraphis noxia Mordv. (in the contemporary Russian literature, this species is known as Brachycolus noxius Mordv.) can be included in this category of FDESPPs. In Russia, this species was described at the end of XIX century, when it occurred to be very abundant. In fact, N.A. Kholodkovsky (1912, p. 488) reported that this species (at that time, it was used the name the barley aphid, Brachycolus korotnevi Mordv.) was appeared sometimes in huge masses in south of Russia, and its imagoes composed vast clouds. Probably, this species penetrated into this country shortly before the outbreak. Eventually, density of this species has become Low although breeding of resistance cultivars has not been conducted.

Contemporary literature does not report about outbreaks of this species in the areas of its former abundance in East Europe. Diuraphis noxia is mentioned as a satellite of more important pest - Sitobion avenae in south Ukraine (Nikolenko and Omel'chenko, 1974). In the Forest-Steppe zone, the role of the aphid is considered as insignificant. In fact, the studies in 1976-1979 showed the presence of four species of aphids on the winter wheat, including Diuraphis noxia, however, the occurrence of Sitobion avenae equaled 92.4% (Dudnik, 1983, p. 6).

In East Germany, participation of Sitobion avenae in a total aphid stock on the winter wheat was about 90% (Assman and Wetzel, 1990) that also suggested the minor role of Diuraphis noxia.

It was reported that Diuraphis noxia is a species of the Central Asia origin (Schliephake et al., 1998). It spreads westward beginning with XIX century. The Low density of this species in Europe in nowadays might be explained by adaptation of resident natural enemies to suppress it.

FDESPPs 8.1.1. cooperates with FDESPPs 8.6.1. "Invasion of exotic taxa of phytopathogens or herbivores, which are able to overcome 2.1.1.2."


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