Diatraea saccharalis

[ RNASeq transcripts ]

The sugarcane borer (Diatraea saccharalis; Lepidoptera: Crambidae) is an important insect-pest for grasses in general, but it is considered one of the main pests of sugarcane. This insect species has economic importance in rice (Oryza sativa), sugarcane (Saccharum officinarum), maize (Zea mays), pastures, sorghum (Sorghum bicolor) and wheat (Saccharum officinarum). The association of this pest with the cultivation of maize is not new. More specifically in Brazil, with the expansion of sugarcane in the country, an increase in the problems of both sugarcane and maize was expected, but what has actually happened is the increase in the incidence of the pest in maize, regardless if the maize field is close or distant from sugarcane fields. More precisely in the cultivation of sugarcane, the attack of D. saccharalis caterpillars on young plants can cause death at the growth point, a symptom known as “dead heart”. Besides that, the attack of caterpillars on adult sugarcane results in the opening of galleries in the culms, causing a reduction in their weight and in the productivity of the sugarcane field. When transverse galleries are formed, there is a favor for breaking the stems by the action of the wind. Symptoms of aerial rooting and the appearance of lateral shoots can also occur due to the attack of this pest. But this insect does not only cause direct damage, some indirect damage can occur, such as predisposing sugarcane plants to fungi attack in open galleries, such as the genus Colletotrichum and Fusarium, which cause culm red rot desease. Such fungi reduce the quality of the cane, decreasing the purity of the juice and the industrial yield in the sugar and/or ethanol production process. The occurrence of the sugarcane borer is favored by high temperatures and large amounts of rain. Even present in all sugarcane and maize producing regions in Brazil, the Center-South region has been the most affected. The favorable climate in this region may be one of the factors responsible for the most significant attacks. In this region, the sugarcane borer can occur throughout the year, however, the highest population levels have been identified in spring and summer.

The D. saccharalis life cycle is very well known in sugarcane, where the insect undergoes complete metamorphosis in the period of 57-67 days and pass through 4 stages of development: egg, caterpillar, pulp and adult. The moth is generally straw yellow in color and in general the female is much larger than the male. The moth is straw yellow in color and, in general, the female is much larger than the male. The eggs have an oval and flat shape and the color varies from white, at the time of laying, to orange until black at the time of hatching, which occurs in an interval of 4-9 days. Oviposition begins at dusk and continues through the night, and usually occurs on the leaf or stem of sugarcane. The eggs are placed in clusters in a nested form (in the form of fish scales) in numbers ranging from 5 to 50 eggs. Hatching can vary according to temperature (heat speeds up the process). Each posture is presented forming a mass, with a disposition that resembles the shape of "fish scales". The incubation period is around 6 days, at which point the caterpillar hatch (“borers”). The average caterpillar period is 44 days, which may vary according to the period of the year. The caterpillar is white with a brown head and, depending on the season, can show different colors. In the summer it may have brown spots and stubborn hair coming out of the spots. In winter, these hairs leave where the spots could appear. Usually, the caterpillar stage presents five or six instars, depending on the environment, and the caterpillars tend to start to feed on the leaf blade or in galleries in the central vein soon after hatching. After the first ecdysis, the caterpillars penetrate the stem by its tenderest part, close to the plant's sheath, making perforations from the bottom up. Next, the pulps have pointed and prominent tubercles in the distal segments. The color of the pulp varies from yellowish-brown to dark brown, and are formed within the galleries created by the caterpillar, for a variable period of 9 to 14 days, until adult moths with numerous lines of brown color emerge along the anterior wing, with nocturnal habit and 5.2 days of life, on average.

The control of D. saccharalis can be done in several ways. Populations of this insect pest can be controlled by spraying with triflumuron, lufenuron or fipronil, directed to the heart of palm, when there is 3% of the sugarcane plantation with newly hatched caterpillars. n addition, due to the feeding behavior of the pest, and the damage caused, the development of research with biological control of D. saccharalis, especially with parasitoids Cotesia flavipes (caterpillar parasidoid) and Trichogramma galloi, (egg parasidoid) made possible a considerable reduction of losses and the maintenance of the agricultural productivity potential of the sugarcane culture. However, the accelerated expansion of sugarcane to new agricultural frontiers in recent decades, and the difficulty in maintaining adequate pest management, has led to a considerable increase in the damage caused by this insect in recent years. And as the history of sugarcane has shown us in the last centuries, research and innovations are advancing, and new theories and technologies are incorporated into Integrated Pest Management in the culture, as currently the commercial use of Biotechnology, enabling us to expand the strategies and tools for monitoring and controlling the sugarcane borer and other important pests in this and other agricultural crops. A recent report from the Plant-Pest Molecular Interaction Laboratory - LIMPP, together with the Bioinformatics Laboratory, both located at Embrapa Genetic Resources & Biotechnology (Brasilia-Brazil), presented a tissue-specific transcriptome (RNA-Seq, Illumina Platform) of D. saccharalis caterpillar, and a differential expression analysis highlighting the physiological characteristics of this pest in response to different diets (artificial diet and sugarcane).