Introduction

Background of the research

The locusts hold a special place among the many species of crop pests because of their notoriety ever since ancient times, when they terrified many countries in Africa and Asia by countless swarms, dooming millions of people to famine and death.

Various natural-economic regions of Kazakhstan are inhabited by about 270 locust species. The greatest hazard to agricultural lands is posed by 15-20 species. Among them the most hazardous species with regard to their abundance and level of harmfulness were specified by the decrees of the Government of the Republic of Kazakhstan no. 697 of August 13, 1993 and no. 1518 of November 26, 2001 and included in the List of especially dangerous pests and diseases of agricultural plants. The most hazardous species are the Asiatic (migratory) locust (Locusta migratoria L.), the Italian locust (Calliptamus italicus L.) and the Moroccan locust (Dociostaurus maroccanus Thund.). Zones of their mass reproduction are located in many regions of the Republic of Kazakhstan. The methods of locust control include mechanical, cultural, biological, chemical and other methods. For the time being the most efficient of them is considered to be the chemical method of control (Kalmakbaev, et al., 2014).

The mass reproduction of locusts, which has lasted in the territory of the Republic of Kazakhstan for more than 10 years, made the researchers pay attention to the Italian locust (Calliptamus italicus l.), Asiatic migratory locust (Locusta migratoria l.) and some species of non-gregarious locusts as the most hazardous pests of agricultural crops. Locust control measures were taken every year during the past five years over the area of tens of thousands of hectares. At the same time intensive expansion of territories contaminated by gregarious locusts was observed, as well as the distribution of locusts from the primary habitats, located mainly in the northeastern areas, virtually throughout the country (Maetal, 2005; Cressman, 2013; Deveson, 2013; Okhotnik, 2004; Hunter, 2004).

The global warming observed over the past decades has caused the desertification of the territory, which in turn has increased the locust threat. The ecosystems of the countries with dry and arid climate, including Kazakhstan, turned out to be most vulnerable to the climate change in general and to the global warming in particular. At the turn of the millennium devastating locust plagues spread to various countries of Africa, Australia, South America, East and South-East Asia (Maetal, 2005; Cressman, 2013; Deveson, 2013).

One of the most powerful manifestations of this natural phenomenon was the outbreak of the mass reproduction and migration of locusts in Kazakhstan, which began in 1997 and lasted until 2003, causing emergencies in all the regions of the country. According to the Federal Service for Veterinary and Phytosanitary Surveillance, the dry periods in southern Russia in the recent years have contributed to the proliferation of the Italian locust and the transition of its population to the gregarious phase, capable of long-distance migration. In the modern context the outbreaks of mass reproduction of locusts are fraught with the most disastrous consequences for the agroindustrial complex and the economy of the country in general, can have a strong effect on the phytosanitary and food security. The total amount of damage caused by locusts in 1999 only in the Pavlodar region, is estimated to be about 2.5 billion tenge. In the Akmola, Aktobe, West Kazakhstan and North Kazakhstan Regions damages to crops and grasslands were observed (Lachininsky, et al., 2002; Kurishbayev, & Azhbenov, 2013).

Rationale for choosing the areas of research.

While the general principles of the dynamics of the population of pest locusts have been studied by many scientists, the specifics of the current locust plague deserve a special study. The search for ways and methods of controlling the population and harmfulness of locusts, which is an important and urgent task, is impossible without the analysis of the current ecological situation in the region and the specifics of the anthropogenic impact on the locust population, including the impact of the large-scale pest control activities.

Most of the research of harmful locusts in the region was carried out in the twentieth century. Currently, the habitat conditions of locusts have changed significantly due to the climate dynamics and the changes in the structure of cultivated lands, largely caused by the anthropogenic impact. This has led to a considerable increase of the agricultural land area, contaminated by locusts, and to significant growth of the harmfulness of locusts for the agricultural crops.

Currently the chemical method of locust control, because of its high efficiency, is used over the hundreds of thousands of hectares, mostly without regard for the environmental consequences of such treatments. Therefore, the research aimed at minimizing the damage for the environment by selecting the most effective range of preparations, is now of high relevance. Expansion of the range of insecticides, which are widely used for locust control, makes the task of determining of their efficiency in different soil-climatic zones especially urgent.

The predominant use of chemical preparations for locust control has gradually led to the depauperization of the beneficial entomofauna, environmental pollution, formation of resistant populations. The resistance has become a factor which destabilizes the phytosanitary situation, so the study of this phenomenon that has become especially characteristic of harmful locusts in the recent years, is currently very urgent.

Currently locusts are one of the most numerous groups of terrestrial invertebrates in the biocenoses of such open landscapes. In many cases, they are the dominant group of phytophagous insects, if not in terms of abundance, then in terms of the biomass. It is therefore not surprising that locusts are known primarily for their practical importance due to the harmfulness of many species. However, locusts also play an important role in the inhabited biotopes, as they, along with some other groups of herbivorous animals (ungulates, rodents and termites) support the endogeneity of mechanisms, which stabilize the biogeochemical cycle at the climax stages in the successional systems of herbal biomes. The role of locusts increases significantly in case of depauperization of other herbivores, in particular in case of reduction of ungulate populations and reduced grazing (Sergeev, 2000; Stolyarov, 2002).

Thus, there is an obvious need for a comprehensive study of locust communities in different landscape zones. Such studies were initiated long before the biocenotic role played by locusts in the biotopes they inhabit was fully realized. As a result, by now extensive factual material on the community structure of these Orthoptera in different regions and landscaped areas has been accumulated.

The analysis of the existing research literature indicates that an important factor determining the structure of locust communities is the microclimatic conditions of a biotope (Bey-Biyenko, 1950; Predtechensky, 1934; Vinokurov, 1915; Rubtsov, 1932; Kambulin, and Bugayev, 1980).

In general, the current state of the fauna and ecological groups of locusts remains underexplored. According to the review data, studies of locusts in different countries, even within the Republic of Kazakhstan, are focused on other quantitative characteristics of soil, climate, plant productivity and profitability of agricultural production (Lachinsky, et al., 2002; Azhbenov, 2000; Nurmuratov, et al., 2000; Azhbenov, 2001; Uvarov, 1966).

Methodology

The research was carried out in 2012-2014 at Zhangir-Khan West Kazakhstan Agricultural and Technical University (Republic of Kazakhstan, Uralsk).

The study of the phenological features and harmfulness of locusts was carried out on the territory of the Syrym and Zhanakala Districts of the semi-desert zone of the West Kazakhstan Region. The selection of areas within the zone of the research was not accidental. The selected areas are the zones traditionally inhabited by the Italian locust and harmful non-gregarious locusts, where active chemical treatments aimed at the locust control have been carried out over a significant area for many years. Locust collection stations were chosen in view of covering the maximum variety of landscapes and biotopes of the studied area.

The survey of crops, pastures, earlier cultivated fields, now withdrawn from the crop rotation, as well as of fallow lands with xerophilous motley grasses was conducted in the area of research.

The composition of the fauna of locusts and the specifics of their biotopical distribution in each geographical point were identified in the result of the route expeditions. The routes were planned in a way as to visit all possible biotopes for several times and get a complete picture of the phenology of imago and biotopical confinement of each species. For this purpose, the frequency of occurrence of imago of various species was estimated in each biotope, while attention was paid to the absence of larvae, adult males or females, the presence of recently fledged (immature) adult locusts; the ecology of species was also determined: the association with certain plants, confinement to the biotopes with specific types of soil, various salinity and moisture levels.

The abundance of locusts in the basic types of biotopes was determined using the method of census at different time points. In each biotope the census was conducted twice in the period of fledging of the imago of the most locust species (late July-early August). Censuses in different biotopes were conducted under similar meteorological conditions and at approximately the same time of day (from 14 to 17) in the periods of high activity of locusts. For all biotopes, where the censuses of locusts were conducted, brief geobotanical descriptions were also provided determining dominant and subdominant plants, length of grass stand, total projective cover on a ten-point scale and the environment of the given biotope.

For the determining of species on the basis of the egg-pods and for the census of the locust population the fundamental guidelines were used (Velikan, 1980; Naumovich, et al., 2000; Chernyakhovsky, 1992).

As part of the research the insecticides currently used for chemical locust control were also studied: Decis-extra, Herold, Tanrek.

The biological efficiency of the insecticides was determined by comparing the number of larvae before and after treatment and making calculations according to the formula: E = a-b x 100%,

where E is the efficiency,%;

a is the abundance of locusts before treatment;

b is the abundance of locusts after treatment;

Results and Discussion

Phenology of locusts

Locust species inhabiting one and the same area often differ significantly in the phenological features of imago. Therefore, in the locust communities there is typically succession of seasonal aspects, each of which is characterized by the emergence of adults of certain types. For the locusts of the semi-desert zone four seasonal aspects can be specified – autumn-spring, spring-early summer, summer, and late summer aspects.

Autumn-spring species overwinter as final instar larvae or imago. In the semi-desert zone locusts overwinter in the embryonic state. Imago of spring-early summer locust species appear in late May – early June and are usually encountered until mid-to late July.

Depending on the latitude and the season the period of the emergence of of adult locusts in the semi-desert zone varies within 7-10 days, but the seasonal aspects and the order of fledging remain almost unchanged. The males of the most species begin to fledge about a week earlier than females. They also earlier begin to die off, and the female of the spring-early summer species are encountered during a month or more after the complete disappearance of conspecific males.

The differences in the phenology of locusts cause partial, and sometimes almost complete reproductive isolation of populations of certain species. For example, the periods of sexual activity of some spring-early summer and late summer locust species virtually don’t overlap. The periods of maximum sexual activity of males of spring-early summer and many summer species overlap insignificantly. Finally, due to the earlier fledging and dying off of locust males the possibility of their contact with females of phenologically later species significantly reduces.

In the course of the research the phenology and the abundance of the most widespread locust species of the semi-desert zone were studied – of the Italian locust (Calliptamus italicus L.) and the Asiatic locust (Locusta migratoria L.)

The Italian locust – Calliptamus italicus L.

Systematic observations of the Italian locust were made in the forage lands of the Zhanakala District over the area of 5.0 thousand hectares.

The spring survey of the egg-pods determined that 3.0 thousand hectares were inhabited by locusts. Egg-pod density in the studied forage land was from 0.8 to 72.8 per square meter. The number of eggs per egg-pod was from 12 to 47. The percentage of damaged egg-pods was from 2.0 to 40.0%.

The reduction of the egg-pod density in the areas of mass egg-laying was also noted (during the autumn survey the egg-pod density varied from 1.0 to 132.8 per square meter), largely due to the destruction of eggs by blister beetle larvae and birds. The abundant rainfall in the period of mating and egg-laying of the Italian locust (40.8 mm of precipitation fell in August while the average monthly rainfall is 24.0 mm, 58.4 mm of precipitation fell in September, while the average monthly rainfall is 25.0 mm), resulted in high soil moisture, which affected the state of the egg-pods. The eggs were scattered, molding of eggs was also observed.

Hatching of larvae in the Zhanakala District began on the 12th of May, mass hatching began on the 20-21st of May.

The instar composition of larvae on the 26th of May was the following: 1st instar – 80%, 2nd instar – 20%.

The monitoring of larvae was completed on the area of 2.0 thousand hectares, the area inhabited by locusts was 1.2 thousand hectares. In 548.8 hectares the density of locusts exceeded the economic threshold. The larval density amounted to 1-36 larvae per square meter, in the meadows – from 32 to 38 larvae per square meter, while the economic threshold is 5 larvae per square meter.

The development of larvae continued 34 days. The phenology of the development of the Italian locust in the Zhanakala District is as follows: First instar: 12.05-20.05; second instar: 20.05-26.05; third instar: 26.05-02.06; fourth instar: 02.06-08.06; fifth instar: 08.06-15.06.

Fledging began from the 8th of June, mass fledging began from the 12th of June. Flying began from the 12th of June, mass flying began from the 17th of June. Mating began from the 21st of June, mass mating began from the 25th of June. Egg-laying began from the 7th of July, mass egg-laying began from the 15th of July.

A survey in the period of mating and egg-laying was carried out over the area of 2000 hectares. 1.1 thousand hectares was inhabited by locusts with a density of 0.1-16 locusts per square meter.

On the basis of the determination of the morphometric indicators of the development phases of the Italian locust it was identified that the amount of locusts in the gregarious phase was from 6% to 65.5%; in the solitary phase – from 7.5 to 60.2%, in the transitional phase – from 19 to 66%.

Dying off of imago began from the 21st of July. 100% dying off of imago was observed in the Zhanakala District from the 14th of August.

The autumn survey of the egg-pods was conducted over the area of 3.0 thousand hectares, 1.7 hectares were inhabited by locusts. Egg-pod density was from 0.8 to 80 per square meter. The maximum egg-pod density was 180 per square meter. The number of eggs per egg-pod was from 17 to 44. The percentage of damaged egg-pods was from 5.0 to 29.0%. Mostly egg-pods are damaged by entomophages (birds, blister beetles), the shrinking of the eggs is also observed.

The Asiatic locust – Locusta migratoria L

Systematic observations of the Asiatic locust were made over the area of 1500 hectares.

Spring survey of the egg-pods was conducted over the area of 1000 hectares, 0.7 hectares was inhabited by locusts. Egg-pod density was from 0.8 to 5.6 per square meter. The number of eggs in the egg-pods was from 30 to 92. The percentage of damaged egg pods was from 10.0 to 40.0%.

The areas which were populated by the egg-pods of the Asiatic locust in the fall of the previous year, were covered with water after spring floods, so there was no possibility to carry out a survey of the egg-pods in these areas. The survey was conducted at the sites of supposed egg-laying.

Hatching of larvae in sands began on the 21st of May in the Zhanakala District. Hatching of larvae in reeds began on the 26th of May, mass hatching began on the 30th of May.

In the coastal zone, in the areas which had been flooded in the spring, hatching of larvae began later, as a result, in the period of treatment there were found larvae of various instars (1st-3rd instars).

Monitoring of larvae was completed on the area of 0.5 thousand hectares, the area inhabited by locusts was 1.0 thousand hectares. In 0.1 thousand hectares the density of locusts exceeded the economic threshold. With the economic threshold of 2 locusts/m² the number of larvae amounted to 1-12 locusts/m².

The phenology of the development of the Asiatic locust in the Zhanakala District is as follows:

Fledging began from the 20th of June, mass fledging began from the 26th of June. Flying began from the 25th of June, mass flying began from the 2th of July. Mating began from the 7th of July, mass mating began from the 14th of July. Egg-laying began from the 17th of August, mass egg-laying began from the 25th of August.

A survey in the period of mating and egg-laying was carried out over the area of 0.5 thousand hectares, 0.1 thousand hectares were inhabited by locusts with a density of 0.006-1215 locusts per hectare.

On the basis of the determination of the morphometric indicators of the development phases of the Asiatic locust it was identified that the the amount of locusts in еру gregarious phase was from 47.5% to 90%; in thе solitary phase – from 5 to 100%, in the transitional phase – from 5 to 34.5%.

Dying off began from the 12th of September.

Autumn survey of the egg-pods was conducted over the area of 1000 hectares, 0.6 hectares were inhabited by locusts. Egg-pod density was from 0.8 to 7.0 per square meter. The number of eggs in an egg-pod was from 30 to 89. The percentage of damaged egg-pods was from 14.0 to 33.0%. In particular, damaging by entomophages and shrinking of the eggs was observed.

Harmfulness of the locusts

The voracity and polyphagia of locusts are the main reasons of their harmfulness. In the semi-desert areas locusts can consume a significant portion of the above-ground phytomass – sometimes up to 30% or more. In case of low locust population density this proportion is a bit smaller, but even then, the impact of these insects on the grass stand is almost always considerable, and during the years of locust plagues they can destroy the green phytomass completely.

The damage to the vegetation of hayfields and pastures is typical manifestation of the harmfulness of locusts. In the hayfields and pastures (both natural and improved) locusts, especially the non-gregarious locust species, usually eat up a part of the leaf blade, but in case of high density they can virtually completely destroy the aerial parts of forage plants. Grasslands often have a very little value, but it may become even lower as a result of the harmful activities of locusts, which in such cases can be compared with overgrazing. The lower is the productivity of hayfields and pastures, the more noticeable will be the damage caused by locusts. In addition to the direct damage the impact of locusts can have long-term negative consequences, expressed in the strong soil degradation, soil erosion and upsetting the water balance of grasslands. The restoration of such land is usually a very long and costly process.

Both gregarious and non-gregarious locust species can cause strongest damage to various agricultural crops. In this case they also usually eat the leaves, but can also eat away at the grain of wheat, “cut” the spikes or panicles of cereals or gnaw through stems at the base. The last type of damage is especially characteristic of adult insects of the gregarious species.

The economic loss caused by such damage to cultivated plants can be significant. Along with the density of the pest, it largely depends on the type of the damaged crop, on the time of damaging and on a number of other factors. It should be noted that the damage caused by locusts is often highly localized and therefore, although individual farms can be literally devastated, on the regional scale the losses often look negligible.

The list of agricultural plants, which can be damaged by locusts, includes almost all the main crops cultivated in the semi-desert zone. For example, only one species – the Italian locust, widely spread in the semi-desert zone, may damage crops of cereals, as well as grasslands and haylands, as well as the migratory Asiatic locust.

In the LLP “Birlik” in the Zhanakala district the Italian locust and the Asiatic locust were found in the pastures and in the spring barley. The maximum locust density was observed in the natural grasslands. The larvae of the Italian locust and the Asiatic locust were found in the 920 hectares of the surveyed 16040 hectares of agricultural lands. In the natural grasslands the maximum density of larvae reached 90 larvae per square meter, in the spring barley – 61 larvae per square meter.

In the farms of the Syrym District, which is situated in the arid area of the region, the maximum density of locusts in the natural grasslands was from 100 to 105 locusts per square meter, in the wheat plantings – 15 locusts per square meter.

In the semi-desert zone in the course of the spring survey of the agricultural lands the egg-pods and the hatched larvae of the Italian locust and the Asiatic locust are mainly observed in the virgin lands, in the grass fallows and in the natural grasslands. During the periods of mass reproductions after hatching of the final instar larvae locusts often migrate to the crop plants. The average density of the locust larvae in the crop plants amounted to 76 per square meter. Damage to the crop plants were insignificant, there was no crop failure, as the further distribution of the larvae and the damage caused by locusts were limited by chemical treatments.

For timely elimination of harmful locusts in the areas of their mass reproduction it is necessary to keep track of all the places of concentration of hibernating egg -pods and monitor the hatching and massive emergence of the larvae of the first and second instars.

However, the locusts, as an integral component of the herbaceous biocenoses, play a significant role in the cycling of nutrients. Locusts don’t just eat the plants; they use as food only a small part of a plant, while crumbling and grinding up the rest of it. Thus, they create a mass which is suitable for further use and processing by other animals, as well as fungi and bacteria. Furthermore, it was shown that in the intestines of locusts the processed plant mass is enriched with B vitamins due to the activity of the symbiotic micro-organisms.

Locust control

Currently, in the period of increasing locust population, chemical treatments remain the primary method of locust control. The organization of protective measures in specific farms and areas is based on the surveys conducted in these territories, and on the forecasts of the dynamics of the locust population.

The area of chemical treatment of locusts in the West Kazakhstan Region has significantly increased in the recent years. The range of insecticides used for locust control is currently wide enough. In the recent years both organophosphorus and pyrethroid insecticides have been widely used for locust control. The pyrethroids used for locust conrol include Arrivo, Decis, Karate, Mavrick, Fury, etc. Organophosphorus insecticides include Karbofos, Rogor-S, Fufanon, etc. Besides, widely used are the preparations Mospilan (neonicotinoids), Adonis (phenylpyrazoles), Dimilin (benzoyl ureas).

In the recent years a number of modern preparations, such as Decis-extra, Herold, Tanrek, have been recommended for locust control. As part of our study we tested the biological efficiency of new locust control preparations in the forage land of the Zhanakala and Syrym Districts.

The censuses have shown that during the years of research carried out in two districts the average biological efficiency of the tested insecticides was from 96.8 to 98.2%. The highest efficiency was achieved by using the preparations Herold and Tanrek. The biological efficiency of these insecticides varied insignificantly during the research years within 1-2%. The greatest rate of larval mortality was observed when using Herald-98.2% and Tanrek – 97.7%. When using Decis-extra the larval mortality of the amounted to 94.8%.

Conclusion

Thus, in the semi-desert zone of the West Kazakhstan region the most widespread locust species are the Italian locust and the Asiatic locust. The locust monitoring conducted in the forage areas of the semi-desert zone of the West Kazakhstan Region in 2012-2014 made it possible to identify the specifics of the phenology harmfulness of locusts and to determine the area of their distribution.

The most efficient locust control insecticides are found to be Herold and Tanrek. The biological efficiency of Herold was 98.2%, Tanrek – 97.7%.

Acknowledgements

The study was supported by the Committee of Science of the Ministry of Education and Science of the Republic of Kazakhstan within the framework of the grant funding on the project “Locusts (Orthoptera, Acridoidea): the fauna and ecology in relation to the climate change, improving the forecast of locust population, planning of control measures”.

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