Биологические науки/7. зоология

D. Yu. Rogatnykh, E.V. Aistova

Amur Branch of Botanical Institute-Garden, Far Eastern Branch of Russian Academy of Sciences, 2-nd km of Ignatyevskoye highway, city of Blagoveschensk, 675000, Russia. E-mail: rogatnykh@yandex.ru

Consortium of insect pests and weeds in potato agrocoenosis in the Amur region

The potato (Solanum tuberosum L.) is one of the most important food, feed and industrial crops, which was first taken by the Europeans from the Indian island of Chiloé [1]. However, the potato, cultivated nowadays, does not occur in the wild. The story of the potato in Russia is controversial and knows different versions. The mass production of potato in Russia was launched in 1765, when a decree of the Senate "to initiate potato growing in the country” was issued [2]. The spread of potato in Russia increased in the middle of the 19^th century. Currently, the potato is cultivated in large areas, both on a global scale- it is cultivated in 130 countries on about 20 million hectares [2], and in Russia, where it takes about 3.2 million hectares. Since its consumption per capita is one of the highest, this culture was rightly called "alternative bread" to cereal crops in our country. In the Amur region potato is cultivated in 15 areas. The main ones are Blagoveschensk, Tambovsky and Svobodny counties. Total area of potato crops as of 2011 in the Amur region amounted to 21.5 thousand hectares (http://agroamur.ru/2/2.html).

An integral component of any agrocoenosis are plants, such as weed, insect pests and diseases. In agro-ecosystems of artificial character the relationship between cultivated plants, weed plants and insects is very specific. Evolutionarily, plants produce more biomass to "feed" phytophages. In this sense, the cultivated plants are no exception. However, in the course of a long breeding and careful attendance, cultivated plants have reduced resistance to certain groups of blight and competitiveness to the weeds.

The objective of our research is the study of species of both insect-pests of potato crops and weed.

During the summer season of 2012 we examined eight potato fields (fig. 1) in Blagoveschensk and Tambovsky counties in the Amur region. The research was conducted by through-method. We inspected the margins of the fields, as well as row- spacing from the headland to the center. The description of the weeds’ and insects’ species was made. Census of insects was carried out after inspecting the leaves and stems of plants on the headland, margins and in the center of fields. Photos of pests and the sustained defects were taken.

Weed is the reservoir for the insect's development, which subsequently move on cultivated plants. Therefore, the species composition of the weed is essential for detailed comprehension of insect-plant relationships.

In a potato crop we detected 32 species of weeds belonging to 15 families. Asteraceae (9 species), Poaceae (4 species) and Polygonaceae (4 species) families dominate by the number of species . Malvaceae and Convolvulaceae families are represented by 2 species each; other families (Chenopodiaceae, Lamiaceae, Equisetaceae, Euphorbiaceae, Cannabaceae, Amaranthaceae, Fabaceae, Solanaceae, Commelinaceae, Portulacaceae) – by one species. A significant amount of weeds was observed in the interrow. In some rare cases potato plant was choked by such species as Artemisia stolonifera (Maxim.) Kom., Sonchus arvensis L. and Commelina communis L., Echinochloa crusgalli (L.) P. Beauv., Eriochloa villosa (Thunb.) Kunth, Cirsium setosum (Willd.) Bess, Solanum nigrum L.. They form small single-species "thickets" on the margins of the fields or sporadically spread throughout the whole fields. Such perennials as Cirsium setosum, Sonchus arvensis, Elytrigia repens (L.) Nevski, Convolvulus arvensis L. are called vegetative-mobile plants for their ability to "move" in better conditions, as well as for the ability of clonal longevity. It is believed that the evolution of these types of weeds was stipulated by the augmentation of their vegetative propagation [3]. These facts we recorded in our studies as well.

In all the studied fields land-treatment activities were held. However, the two fields underwent only repeated plowing during the season. Due to these measures, a green manure for next year crops is produced. Besides, it helps to reduce the number of insects and weeds. In other fields, apart from tilling, chemical cultivation was conducted. Another important way to reduce the number of weed and insects species is to implement crop-rotation system (potato – lea - potato, or potato-soy-potato), which was applied in all the studied agro-ecosystems.

In our studies we have noted a slight damage caused to potato by pests. However many species of weeds have inflicted damage to the vegetative and generative organs of the crops of different severity levels – from perforation to skeletization of the lamina. Some groups of insects, when cutting or destroying weed by mechanical or chemical means can become pests.

On weed plants and cultivated potato we have identified fourteen species of insects belonging to two orders and seven families. Coleoptera order was presented by four families, the most diverse of which was Chrysomelidae with five detected species. There were found two species of the Scarabaeidae, Curculionidae and Meloidae families and one species of, Coccinellidae. The Hemiptera order was presented by two species of two families.

The study of the headlands has shown that weed species composition differs from that of the cultivated crops by its scale. Field margins represent the compact plant formation with dominating cereals or sagebrush. Other species belong to the group of typical segetalis, but they outnumber those in the center of the fields. It should be noted that a particularly strong damage to vegetative organs of plants is inflicted by insects on the margins of fields. It can be attributed to the large vegetative masses, which attract a large number of pests, harboring them and providing food.

The representatives of Meloidae – Epicauta sibirica dubia (Fabricius, 1781) and E. Megalocephala (Gebler, 1817) – were the most numerous in almost all of the studied fields. Beetles were found on Commelina communis L., Elytrigia repens (L.) Nevski, Echinochloa crusgalli (L.) P. Beauv., Eriochloa villosa (Thunb.)Kunth, Setaria viridis (L.) P. Beauv. All listed plants were significantly damaged. In addition to the occurrence on weeds, imago Epicauta has been sighted on the leaves of the potato. The high number of different kinds of Exomala pallidipennis (Retter, 1903) was registered, whose beetles browsed potato flowers. It is worth mentioning that they were detected in two fields only, in close proximity to the forest plantation. Another representative of the Scarabaeidae family – Anomala luculenta Erichson, 1847 was found in a small number on weed plants of a single field.

Among Chrysomelidae the most numerous was Monolepta quadriguttata (Motschulsky, 1860), which in addition to potato leaves corrupted adventitious species – Hibiscus trionum L. Chaetocnema concinna (Marsham, 1802) and Phyllotreta nemorum (Linnaeus, 1758) were detected in only two fields, but in some places in large numbers. The greatest damage from flea beetles was exposed to Humulopsis scandens (Lour.) Grudz. A small number of both species was observed on leaves of potato; however these kinds of pests cannot be viewed as inflicting serious damage to the crops. There were recorded cases of flea beetles invading crops of soybeans [4], as well as invasions of milfoil chrysomelid beetle [5] to potato leaves. In both cases these invasions were stipulated by the lack of the species’ fodder plants. We have also registered the habitat shift of Cassida nebulosa Linnaeus, 1758 imago to potato leaves. The larvae of this species were observed in all studied fields on Chenopodium album (L) and Cirsium setosum (Willd.) Bess. The number of individuals per plant varied from single entities up to dozens.

In one of the fields sporadic entities of Entomoscelis orientalis (Motschulsky, 1860) were founds. Few were Chlorophanus sibiricus (Gyllenhal 1834) and Lixus iridis (Olivier, 1807) (Curculionidae), Epilachna vigintioctomaculata (Motschulsky, 1857), and Lygus rugulipennis (Poppius, 1911) and Eurydema gebleri (Kolenati, 1856) (Hemiptera). Of the above mentioned species Epilachna vigintioctomaculata deserves special attention. A serious outbreak of this pest invasion was recorded in the spring of 2011 in the Amur region. In spring 2012 in connection with the large number of the hatched overwinter beetles, an unfavorable forecast about further increases in pest invasions to the fields was made (www.rosselhoscenter.ru). However, due to the adverse weather conditions, they did not happen. Single local outbreaks were observed only in private households, where fields were located close to the forest. This is due to the fact that imago prefer to spend the winter under the plant litter on edges of the woods, from where it expands to agrocoenosis in spring. Along with Mylabris, which are also capable of giving widespread pest outbreaks, Epilachna vigintioctomaculata is the most harmful to potato crops in the Amur region.

Potentially dangerous, but not yet the cause of mass outbreaks are Monolepta quadriguttata and Exomala pallidipennis (fig. 2).

The complicated character of coevolution of insects and plants is indicated by the fact that certain groups of insects can grow only on certain plants. There is currently little data that would make it possible to trace the historical links between groups of insects and their fodder plants. From the point of view of insects-plant system, the changes in weed species composition results in significant changes in the species composition of insects. If quite typical pests were detected in the fields of cultivated crops, others were attracted by the species of weed plants. In such cases, the cultivated plants act as a secondary resource associated with a lack of major fodder species for pests. Zero tillage can reduce the effects of the pests population control, exercised by natural mechanisms.

Index of sources:

1. N.I. Vavilov selected works. In 2 volumes. V. 1. L.: Nauka, 1967. -425 p. (in Russian).

2. Ŝegorec O.V. Amur Potatoes. Bilogizing Technology of Cultivation. – Blagoveschensk: LL Publishing company «Rio», 2007. – 400p. (in Russian).

3. Ulyanova T. Weed Flora in Russia and other CIS Countries. – Spb.: WRI, 1998. – 233 p. (in Russian).

4. Mosejko A.G. Updating of Agricultural Value of Leaf Beetles’ Species (Coleoptera, Chrysomelidae), Damaging Soy in the Far East // Plant Protection. -2010. - № 1. P. 42-47. (in Russian).

5 Costin V. D., Krylov A.V., Ivliev L.A. Milfoil Chrysomela – potential pest of potato in Kamchatka//Report of the Far East division of the Siberian Branch of the Academy of Sciences of the USSR. 1963., ISS. 17.P. 97-99. (in Russian).