The giant sugarcane borer, Telchin licus (Drury) (Lepidoptera: Castniidae), also known as the banana stem borer, is one of the most important pests of sugarcane in Central and South America (Mendonça 1996; Bustillo 2013), although it also attacks banana and pineapple (Lamas 1993). This pest has caused production losses in sugarcane ranging from 20% to 60% in Bolivia, Brazil, Colombia, Central America, and the Caribbean (Rios & Gonzalez 2011; Valencia et al. 2014). In the central region of Colombia, the pest can be problematic in sugarcane grown for panela, a local unrefined sugar product, whereas in the western and eastern regions, it damages cane grown for refined sugar and ethanol production. Feeding damage by T. licus not only reduces biomass and sucrose content, but also reduces the ratoon available for planting the next crop (Bustillo 2013; Gonzalez et al. 2017).

The adults are large, diurnal moths with clubbed antennae that often are mistaken for butterflies, and mature larvae can reach 14 cm in length. Female moths oviposit at the soil next to the base of stems and, upon eclosion, neonate larvae quickly bore into the stem where they remain feeding on the rhizome and stems until pupation, which generally occurs at the base of the stalk. Adult emergence holes, which are cut by the larva prior to pupation, usually are located close to ground level (Negrisoli et al. 2015). The species has 2 generations per yr, requiring from 4 to 6 mo to complete its life cycle (Bustillo 2013), which results in 2 peaks of adult emergence in eastern Colombia, 1 at the beginning of the rainy season (Apr–May) and another at the end (Oct–Nov). The ecology of T. licus has been studied in Brazil (Garcia & Botelho 2009) and Costa Rica (Salazar et al. 2018). The complete life cycle requires approximately 180 d: the incubation period lasting from 9 to 13 d, larval development from 98 to 210 d, and the pupal stage from 28 to 35 d, with adults living from 3 to 16 d.

Management of the pest is difficult because of its endophytic habits; attempts to manage T. licus with insecticides and entomopathogenic fungi have proven ineffective due to larvae feeding in protected locations within the stalks (Craveiro et al. 2010; Fonseca et al. 2015). Some sugarcane genotypes seem to differ in pest incidence, but truly resistant varieties have not been identified (Dinardo-Miranda 2008). Bacterial sub-species of the Bacillus thuringiensis Berliner (Bacillales: Bacillaceae) group have been isolated from the digestive tract of T. licus, suggesting the potential for using pathogenic strains of these bacteria against the pest (Rocha et al. 2021), although this approach has not yet been adequately explored. Application of the entomopathogen Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) via sub-surface drip irrigation systems has proven relatively effective in controlling T. licus in trials in Brazil (Krontal 2014), but such irrigation systems are rarely used in Colombia. Systemic insecticides (e.g., chlorantraniliprole) are used commonly to manage T. licus, either by spraying the stubble post-harvest, or by spraying the regrowth 2 to 3 mo later, which can reduce the larval population by up to 76% (Dario et al. 2014; Negrisoli et al. 2015; Garcia & Botelho 2016). Foliar applications of broad-spectrum insecticides also may reduce adult populations and pest injury in commercial fields (Pabón, data unpublished).

Soil mounding is a cultural practice often employed in annual and perennial crops for a variety of agronomic purposes. In sugarcane production, mounding of soil around the base of plant stems can be used to help anchor plants by increasing the volume of soil available for lateral root growth, reduce weed competition, and improve soil aeration and water infiltration (Cassalet et al. 1995). Mounding can be accomplished manually using conventional tillage tools (hoes and shovels) or mechanically using tractor-driven tillage implements. Typically, the objective is to increase the height of the soil from the bottom of the furrow to the exposed base of the plants by 15 to 20 cm (Ortiz-Cañavate et al. 2012).

Mounding of soil around the base of sugarcane plants is a cultural practice frequently used to control weeds and improve rooting, but its potential for managing pests that attack the rhizome of the plant has not been evaluated. Coverage of rhizomes with harvest residues was reported to reduce sugarcane stalk damage by the stem borer Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae) (Sandhu et al. 2011). However, Cherry & Sandhu (2020) found no effect of tillage treatments on soil arthropods in Florida sugarcane. Given the biology of T. licus, we hypothesized that mounding soil over the lower portion of plant stems prior to emergence periods would trap vulnerable callow adults inside sugarcane stalks. The purpose of our study was to determine the impact of this cultural practice on T. licus. The study focused on evaluating how either manual or mechanized mounding of soil around the base of stalks could impede the emergence of adult borers under field conditions.

Materials and Methods

Results

MECHANICAL MOUNDING

Pre-trial sampling in the field estimated T. licus density at 3.6 ± 0.3 immature life stage per 2 m of a row, for an estimate of about 12,000 per ha, given a 1.5 m row spacing. Weekly counts of T. licus adults were higher significantly in control plots than in treatment plots, regardless of mounding height (F = 5.18; df = 2, 33; P = 0.011). There was also a significant effect of time (F = 2.14; df = 9, 33; P = 0.026), indicating that more adults emerged over the first 4 wk than later on, but the interaction between treatment and time was not significant (F = 1.31; df = 18, 297; P = 0.177; Fig. 3). Longitudinal comparisons of means were not justified because analysis of orthogonal components indicated non-homogeneity of variance (χ² = 161.36; df = 44; P < 0.001), rendering pair-wise comparisons dependent on sphericity inappropriate.

Cumulative adult emergence varied significantly among treatments (F = 5.26; df = 2, 22; P = 0.013), with almost 3 times as many T. licus adults emerging in control plots compared to plots with a mounding treatment, and no difference between mounding heights (Fig. 4). This amounted to a 65% reduction in adult emergence, which translated into a reduction of about 5,600 adults per ha.

Fig. 1.

Mean number of Telchin licus adults (± SE) emerging weekly per sugarcane plot. Plots received 1 of 2 treatments: manual mounding of soil to a height of 20 cm around the base of plants (circles, solid line), or control with no soil disturbance (squares, hatched line). The effect of treatment was significant (repeated measures ANOVA, P < 0.05), but effect of time and treatment*time interaction were not (P > 0.05).

Fig. 2.

Cumulative mean number of Telchin licus adults (± SE) that emerged in sugarcane plots receiving 1 of 2 treatments: manual mounding of soil to a height of 20 cm around the base of plants, or control with no soil disturbance. Treatments were marginally different (1-way ANOVA followed by Fisher's LSD test, α = 0.05).

Discussion

Soil mounding, whether applied manually or by machinery, significantly impeded the emergence of T. licus adults from infested sugarcane stalks, reducing adult moth emergence by 64% and 65%, respectively. Thus, a layer of soil 10 cm in depth around the base of plants was sufficient to prevent T. licus adult moths from reaching the soil surface, likely because they lack either tarsi or mouthparts that would enable digging behavior. Thus, control by burial is likely to be less affected by soil properties such as texture, moisture content, temperature, or degree of compaction than it is for other insects that naturally pupate in litter or soil (Chen & Shelton 2007; Renkena et al. 2012; Matlock et al. 2017; Hooper & Grieshop 2020). Similarly, mounding of soil around the base of apple rootstocks can provide 76 to 99% control of dogwood borer, Synanthedon scitula (Harris) (Lepidoptera: Sesiidae) (Gut et al. 2005). However, in the latter case, rather than impeding adult emergence, mounding functioned largely by preventing callous burr formations that neonate larvae use to enter the trunk via associated cracks and fissures.

Fig. 3.

Mean number of Telchin licus adults (± SE) emerging weekly per sugarcane plot. Plots received 1 of 3 treatments: mechanical mounding of soil to a height of either 10 cm (circles, solid line) or 20 cm (triangles, hatched line) around the base of plants, or control with no soil disturbance (squares, hatched line). Main effects of treatment and wk were significant (repeated measures ANOVA, P < 0.05), but the interaction between treatment and time was not (P > 0.05).

Fig. 4.

Cumulative mean number of Telchin licus adults (± SE) that emerged in sugarcane plots receiving 1 of 3 treatments: mechanical mounding of soil to a height of either 10 or 20 cm around the base of plants, or control with no soil disturbance. Means bearing different letters were significantly different (1-way ANOVA followed by Fisher's LSD, α = 0.05).

These experiments were conducted in the mo of Sep (manual) and Apr (mechanical), respectively, with mounding treatments timed to coincide with biannual generations of the pest, each targeting the pupal cohort just prior to emergence. However, a fraction of adults did emerge successfully in treatment plots, likely through emergence holes located in portions of stems that remained above the soil post-treatment. Furthermore, not all the soil deposited by the mounding treatments resulted in burial of stalks to the same depth, which may have permitted some adults to escape through emergence holes close to the soil surface. Similarly, when larvae of Cydia pomonella L. (Lepidoptera: Tortricidae) were buried at different depths, a fraction of adult moths managed to emerge successfully (Baughman et al. 2015).

In mountainous regions of Colombia, manual mounding could be a suitable alternative for managing T. licus, whereas mechanical mounding would be appropriate for more industrialized areas with level fields. Soil mounding is relatively easy to apply, inexpensive, and compatible with other control practices. The current cost of mechanical mounding is around USD $16 per ha, whereas insecticide applications cost around USD $22 per ha for control of adults, and around USD $25 to $39 per ha for control of larvae, depending on equipment and active ingredient used. Nevertheless, soil mounding is regarded as a supplementary integrated pest management tactic that can be employed together with others to improve population control and damage reduction. Contrary to expectation, deposition of a deeper layer of soil around the base of plants (20 versus 10 cm) did not increase the level of control obtained in the mechanical mounding experiment, so if a critical depth of soil is required, it is less than 10 cm.

Burial via tillage also can provide effective control of pests that pupate in litter on the soil surface, such as the grape berry moth, Paralobesia viteana Clemens (Lepidoptera: Tortricidae) (Matlock et al. 2017). Burial of mature larvae of the codling moth, C. pomonella, below a depth of 1 cm resulted in complete mortality of all insects (Baughman et al. 2015). However, tillage and burial also have potential for controlling pests that pupate within plant material or crop residues. For example, tillage does not harm overwintering larvae of the sunflower stem weevil, Cylindropturus adspersus (LeConte) (Coleoptera: Curculionidae), but post-harvest burial of sunflower stalks to a depth of 15 to 20 cm provides almost complete control of emerging adults (Charlet 1994). However, burial to a depth of 30 cm was required to prevent emergence of pine shoot beetles, Tomicus piniperda (L.) (Coleoptera: Scolytidae) from infested pine logs (Haack et al. 2000).

In annual crops, various forms of tillage can impact pest populations directly via burial or physical injury, or indirectly via effects on the survival of their key natural enemies (Stinner & House 1990). Although no-till production systems tend to enhance biological pest control by increasing arthropod diversity and improving the survival of beneficial species (Tamburini et al. 2015; Mesmin et al. 2020), they also can favor the survival of certain pest species. In cotton, for example, populations of boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), and bollworms, Helicoverpa zea Bodie (Lepidoptera: Noctuidae) and Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), are favored by no-till practices because tillage reduces the survival of their pupae in the soil (Henneberry & Clayton 1979; Gaylor & Foster 1987; Henneberry et al. 1991). In apple orchards, survival of mature larvae of the codling moth, C. pomonella, can be reduced to zero by burial under 1 cm or more of sand (Baughman et al. 2015).

One assumption implicit in this approach is that a reduction of adult emergence within the crop will result in population reduction and less damage from subsequent generations. This will be the case only if sugarcane-infesting cohorts of this moth rely predominantly on sugarcane to maintain their population numbers, and will be less effective if significant numbers arrive either as emigrants from distant (unmanaged) fields, or from alternative wild host plants. Therefore, further evaluation of the efficacy of soil mounding as a control tactic for T. licus will require its continuous implementation in specific localities for several yr, and integration with other control tactics as part of an integrated pest management program, with moth numbers carefully monitored to see if regional populations can be reduced significantly over time.