Elasmus caterpillar in soybean crops: lethal attack

Several insects occur throughout the soybean cycle, causing damage. Among those that attack in the initial phase, the elasmo caterpillar (Elasmus palpus lignosellus), (Zeller, 1848), which can cause  the death of plants,  with firepower to reduce population density (stand) and harm production.

The incidence of the collar borer or elasm caterpillar is generally cyclical, but outbreaks in soybeans have been frequent, especially in sandy soils and in years with prolonged drought, in the initial phase of crops. However, depending on the severity of the drought, they generally attack all texture variations. This pest also occurs in other crops, such as corn, beans and cotton if there is a summer period at the time of planting. It tends to be common in new cultivation areas that were under degraded or native pasture conditions.

In the 2014/15 harvest, attacks by this insect occurred in all regions of Mato Grosso, in the first sown areas, due to the lack of humidity at the time of plant emergence, even in regions such as the north of the state, where the incidence of this insect is not common. elasmo caterpillar because it is an area where rains begin regularly. In this harvest, elastic damage was observed and some areas needed replanting, due to the large area attacked, causing death of the plants.

Generally the attack occurs at the beginning of germination, however, when prolonged summer periods occur, elasm caterpillar damage can be observed in plants with more advanced stages and, in this harvest, it was also possible to verify the damage in January, when the The plant was in the V7 development stage, 25 to 30 days after emergence due to drought during this period of the year.

Description and Biology

It has a polyphagous habit, feeding on different species of plants, such as grasses and legumes, for example.

The caterpillar has a color ranging from bluish-green to pinkish, with brown transverse stripes and a small head, also brown. It can reach 16mm at maximum. As soon as it attacks the plant, the caterpillar builds a shelter made of web and grains of sand near the plant's entrance hole, remaining there when it is not inside the gallery. They are very agile, when touched they jump incessantly for a few seconds, this behavior being a way of getting rid of natural enemies. The pupa forms in the soil, close to the base of the plant and initially presents a yellowish or green color, turning brown and, just before the emergence of the adult, it takes on a black color.

The adult is a gray micro-moth that measures 15mm to 23mm in wingspan, the wings are arranged parallel to the body line and it is very attracted to light sources. The eggs are deposited on the plant, in the soil or in plant debris in the area, such as straw. Soil moisture directly affects adult behavior in site selection for oviposition, caterpillar hatching and mortality of newly hatched caterpillars.

Different cropping systems are factors that also affect the population dynamics of this insect. Infestation is greatly reduced in direct planting, when compared to that which occurs in the conventional planting system. Areas burned before planting also maintain larger infestations, where in addition to being attractive to insect adults, smoke stimulates oviposition, providing twice the number of eggs when compared to the absence of smoke (MAGRI, 1998).

Lifecycle

The average duration is 42 days (egg = 3 days; caterpillar = 20 days; chrysalis = 7 days; adult = 12 days).

Attack period

It begins shortly after soybean germination and can last for 30 to 40 days. The insect is often already present in the area before the crop is installed, making it necessary to be aware of possible infestations in neighboring crops and take into account the occurrence of a prolonged dry period. Hence the importance of inspecting the area or straw before sowing.

Damage

When small, the caterpillars feed by scraping the leaf parenchyma. As they grow, they drill a hole in the plant at ground level, creating an ascending gallery that increases in length and width as the caterpillar grows and consumes food. At the entrance to this gallery, you can see the shelter formed by debris linked together by silk threads secreted by the caterpillar, used to move between the attacked plants and also as a shelter in the pupal stage.

The attacked plants initially wither and may die immediately, leading to stand failures or suffer worsening damage later, under the action of rain, wind or agricultural implements, which topple the plants. It is often a pest that leads to stand failures and, occasionally, requires re-sowing in crop gaps or in the entire area.

In corn cultivation, in some years damage occurs from the elasm caterpillar, caused in the collar region, then penetrating the stalk and creating galleries inside, which causes tillering and/or death of the plant. 

Control

Soils under direct seeding systems, as they generally retain more moisture, have fewer problems with pests. Areas without roofs and that suffered from fire in the off-season tend to present greater damage as they favor the development of caterpillars.

High soil moisture is the main abiotic factor that can be used in elasm management. It acts negatively at any stage of the pest's biological cycle. However, its importance is greater at the beginning of the larval stage, causing high mortality. As the caterpillar develops, mortality decreases (VIANA & COSTA, 1992). High soil moisture also negatively affects the behavior of adults in selecting oviposition sites and hatching caterpillars. Moths prefer to lay their eggs in drier soils. Oviposition is greater in dry soils than in wetter soils.

Seed treatment with carbamates (thiodicarb and carbosulfan), fipronil or chlorantraniliprole in appropriate dosages can be a measure that minimizes the problem. However, the risk of phytotoxicity is high, and the recommending professional must be careful about registering the insecticide for the crop. Soybean seeds, especially those treated with carbamates, must be immediately sown in moist soil to avoid worsening phytotoxicity and allow adequate plant emergence immediately after sowing. Spraying an insecticide with good depth action such as chlorpyrifos, preferably done at night, in a high volume of spray (400 L/ha to 600 L/ha) on the plants, can control the pest with up to 60% efficiency. In situations of extremely high populations of the pest, the use of chlorpyrifos incorporated pre-planting, or sprayed in the sowing furrow (0,10 meter range in the furrow), increases the pest control effectiveness in relation to aerial part sprays. . The ideal is to sow soybeans as soon as rainfall in the region becomes regular, as the most effective control of the pest is achieved by good soil moisture.

In studies carried out in the soybean harvest, with seed treatment, the damage was more intense at the beginning of plant development due to the high pressure of caterpillars during this period and there was a difference between the products used and the number of plants attacked was higher for the area without seed treatment (control), as well as among the treatments carried out (Table 1). For the number of caterpillars present in each treatment, no statistical difference was observed in the evaluations carried out. This is due to the difficulty in finding the caterpillar, which moves from one plant to another during the cycle, and in plants with symptoms of damage, caterpillars are generally not found, as they have already migrated to other plants.

Table 1. Average number of plants attacked by elasmos caterpillar and average number of elasmos caterpillars from each seed treatment in conventional soybean. Itiquira/MT. 2014/15 harvest.

	7 days after emergence
	Plants attacked1	###P#2	caterpillars1	###P#2
Witness	71,75 to	-	3,25 to	-
Fipronil + Pyraclostrobin + Methyl thiophanate (100mL/ha)	34,25 bc	52,3	1,75 to	46,2
Thiamethoxan (250mL/100kg of wk)	61,00 ab	15,0	2,00 to	38,5
Chlorantraniliprole (100mL/100kg of wk)	20,50 c	71,4	0,75 to	76,9
CV%	15,04	-	28,44	-

 

7 days after emergence

 

Plants attacked¹

###P#2

caterpillars¹

###P#2

Witness

71,75 to

-

3,25 to

-

Fipronil + Pyraclostrobin + Methyl thiophanate (100mL/ha)

34,25 bc

52,3

1,75 to

46,2

Thiamethoxan (250mL/100kg of wk)

61,00 ab

15,0

2,00 to

38,5

Chlorantraniliprole (100mL/100kg of wk)

20,50 c

71,4

0,75 to

76,9

CV%

15,04

-

28,44

-

¹Plants attacked and caterpillars present within 60m²

² Control Efficiency (%)

A stand reduction was observed in untreated areas in relation to the seed treatments carried out, where treatments with Fipronil and Clorantraniliprole offer lower percentages of final stand loss in relation to the stand observed 7 days after emergence, which indicates that the Seed treatment offers protection to plants in the initial phase of development against the elasm caterpillar and, among the treatments, there is a difference in control. In this area, lower yield was also observed for the untreated area in relation to the treated areas, and treatment with Chlorantraniliprole offered higher yield in relation to the other treatments.

 

Table 2. Percentage of final stand reduction by seed treatment in conventional soybeans and yield (kg/ha). Itiquira/MT. 2014/15 harvest.

 

		Performance kg/ha
Witness	62,5%	2294,0 to
Fipronil + Pyraclostrobin + Methyl thiophanate (100mL/ha)	20,2%	3246,2 to
Thiamethoxan (250mL/100kg of wk)	39,5%	3349,9 to
Chlorantraniliprole (100mL/100kg of wk)	15,0%	3469,1 to
CV%		9,85

 

 

Performance

kg/ha

Witness

62,5%

2294,0 to

Fipronil + Pyraclostrobin + Methyl thiophanate (100mL/ha)

20,2%

3246,2 to

Thiamethoxan (250mL/100kg of wk)

39,5%

3349,9 to

Chlorantraniliprole (100mL/100kg of wk)

15,0%

3469,1 to

CV%

 

9,85

 The article was published in issue 190 of Cultivar Grandes Culturas.