The populations of Stenoma cecropia associated with oil palm in Central America are normally under control by its numerous natural enemies, but occasional outbreaks have occurred in the past in localized areas. This review describes some details of past outbreaks, important aspects of the pest (taxonomy, anatomy, life cycle, behavior and natural enemies), its potential to cause economic damage and the possibilities to manage the pest through an integrated approach.

Economically important moths in the Stenomidae family have not been very well studied in tropical America. However, Stenoma cecropia is one of the species better understood, particularly when associated with oil palms. Since this species was initially found associated with cacao in Ecuador, it was thought that it adapted to the oil palm from this original host.

The pest has caused important defoliations in oil palm plantations in South America, particularly in Ecuador and Colombia (Genty 1978). In Costa Rica, important outbreaks occurred in 1973 in the Central Pacific coast, and since then some population increments have occurred sporadically. This work is a review of the biology, ecology and management of the specie, with emphasis in oil palm plantations in Central America.

Both leaf miners and defoliators occur in this rather small family. Larvae feed on a large variety of forest species and fruit trees (Borror and White 1970).

The adult of S.cecropia is a small rose-brown moth with a turf of dark scales on the prothorax surrounded by large brown-orange scales (Figs. 1, 2). The anterior wing is rectangular in shape, brown, with pale violet zones, and with two fine transversal lines formed with dark scales. The posterior wing is rounded, gray, and with zones orange to yellow (Genty 1978). The ventral part of the body is rose, and the legs are whitish. Sexual dimorphism is not very well marked: females are about 26 mm and males 23 to 25 mm.

Eggs measure 0.9-1.0 mm, are oval in shape, rather flat and transparent, with about 15 longitudinal lines forming polygonal marks. Newborn larvae have almost no pigment, and then (second instar) the anterior end becomes clear brown and longitudinal clear red bands develop along the dorsal part of the body (last two thoracic segments and first three abdominal ones). As the larva ages the cephalic cage and the thorax darkens, and the rest of the body takes brown-purple coloration.

As the larva grows, it builds a sheath made with plant materials and body secretions. This sheath takes the shape of an “abundance cone” as the larvae enlarges it to accommodate its growing body (Fig.1). The Spanish common name "gusano tunel" (tunnel worm) refers to the shape of the sheath built by larvae. The larvae have three pairs of long tactile setae on segments 1, 2 and 8 which are always in contact with the silk that internally covers the sheaths and extends beyond the entrance. When disturbed, the larvae can make a fast retreat to the safety of the sheath. Pupae are naked, yellow first and then red brown.

Eggs are laid on the leaflets, near the central vein. Upon hatching, larvae migrate to the lower portion of the leaflets and start to build the protective sheath. First larval stages feed superficially on the lower surface, and these wounds are usually invaded by opportunistic pathogens such as Pestalotiopsis spp. and others. Larger larvae move outside the protecting sheath and feed through the leaf lamina, usually on both sides of the central vein. This feeding habit causes a characteristic constriction on the leaflet, where the apical portion may completely dry out (Fig. 3).

Adults are nocturnal, and during the day they rest on different plants (Fig. 2). Males respond to artificial light, but females do not, so light traps are not very efficient as a control strategy. In a similar way, food baits are not useful since adults do not feed as they have its buccal parts atrophied. The life cycle takes 58 to 67 days ( Table 1 ), not considering the adult stage, which only last for a few days. Females are borne with a full load of eggs, and following mating, the eggs are laid single or in small groups along the central vein of the leaflets. After laying the eggs, the females soon dies after.

Larvae when feeding cause direct damage, but there is also an important indirect damage caused by the invasion of wounds by opportunistic pathogens such as Pestalotiopsis spp. and others. The particular feeding habits of the larvae also cause that large portions of untouched apical tissue of the leaflets eventually dries out after becoming isolated when the larvae feed on both sides of the central vein. Larval density may be as high as 1000-3000 per leaf.

In oil palm plantations of Costa Rica, important outbreaks were observed in 1973, 1983, 1984, 1990, 1991, 1998 and 2004. In 1973, 1416 ha were affected and severe damage occurred in 342 ha in a commercial plantation in the central Pacific coast (Quepos). In 1990, the pest appeared again, in two neighbor areas (165 and 117 ha). This time up to 3000 larvae/leaf (nº 17) were counted, and many plants suffered defoliation estimated in 80%. Next year, in 1991, a total of 200 ha were affected, but this time larval counts were much lower (up to 58 larvae/leaf 17). During the rainy season of 2004, damage was severe in several hundred hectares

Females are very mobile and within a few generations the pest may extend to large areas within a plantation. It is thought that this behavior allows the insect to escape from its natural enemies by colonizing new area where the population of them is lower.

A larva needs about 60 cm² of tissue to complete its development, but as pointed out before, total damage is increased by the attack of fungi like Pestalotiopsis spp., and the fact of large portions of the foliage (apical sections of leaflets) drying out when the larvae feed on both sides of the central vein. This feeding habit may help the larvae (sheath) to camouflage themselves from predators like birds. Table 2 summarizes the feeding capacity of larvae, so to have an idea of the number of them that can be allowed without causing an economically important damage.

There are several parasitoid wasps that attack this pest, but Rhysipolis sp. (Braconidae) seems to be the most important. This wasp is a true ecto-parasitoid (it feeds from the outside of the larvae), and attack the 5th larval stage where 3 to 8 individuals can be found. Upon completing their development, the parasitoid builds some cylindrical cells separated by waxy walls along the tunnel (sheath). Parasitism may reach 7-20% of larvae.

Elasmus sp. (Elasmidae) is another parasitoid found in larvae, but it could well be a hyper parasitoid of Rhysipolis sp. The tachinid fly Euphocera floridensis has also been found parasityzing S. cecropia (Delvare and Genty 1992). Pupae can be attacked by Brachymeria sp., B. subconica and Pseudobrachymeria sp. (Chalcididae) (Genty 1989), but their populations are usually low.

In Costa Rica, during the outbreaks in 1990, the wasp Trichospilus diatrae (Eulophidae) was prevalent. Between 165 and 280 individuals/pupa were found and up to 40% of the pupae were affected (Mexzón and Chinchilla 1996). Several spiders ( Gasteracantha cancriformis , Leucage mariana , Mangora sp., Plesioneta argyra , one species of Clubionidae and two speceis of Salticidae) were seen feeding on larvae and the adults of S. cecropia . A rather small Salticidae (5-6 mm, orange prosoma and opistosome cream with black dots) was particularly active.

Several pentatomid bugs ( Alcaeorrhynchus grandis , Mormidea sp., Podisus sp and Proxys sp.) were also abundant (Fig. 4). A fungal attack and other diseases (Fig. 4) eventually affected near 80% of the larvae.

Many of the parasitoids of S. cecropia were seen feeding on several plants associated with oil palm plantations. Adults of Rhysipolis sp. were seen on the extra floral glands of Cassia reticulata , Cassia tora , Byttneria aculeata , Melanthera aspera , Synedrella nodiflora and Scleria melaleuca . Brachymeria sp. was found on Amarantus spinosus , C. tora , M. aspera , Spermacoce lavéis, and tachinid flies on Chamaesyce hirta, S. melaleuca and Vitis sycioides.

Most of these plants require plenty of sun light to grow and synthesize the compounds needed by the adult stage of these parasitoids. These plants should be protected and planted along areas where they do not interfere with the normal operation of the plantation (along drainage canals, roads and other open spaces available). Combining several of these species may be even more efficient to sustain a healthy population of parasitoids.

IPM principles applied against S. cecropia are the same of those used against other defoliators such as Oiketicus kirbyi and Opsiphanes cassina (Mexzón et al. 2003, Chinchilla 2003). The whole program is based on a timely done sampling, so any potential outbreak can be detected early.

Once a potential outbreak is detected, attention is paid to asses the population of natural enemies, and to evaluate its potential as the sole regulators of the outbreak. Any IPM program must consider the following aspects:

1. Development and implementation of a fast and reliable sampling method for the population of larvae on the leaves
2. Assessing the population of predators (particularly pentatomid bugs), parasitoids and other natural enemies of the pest.
3. Identification of actual foci where the pest concentrates: an appropriate field sheet has to be designed to collect the pertinent information on larvae and natural enemies
4. All information has to be rapidly processed to serve as the base for the control strategies.

When the insect is under control, the few larvae found tend to concentrate on the leaf-lets at the distal portion of the oldest leaves, particularly those facing open areas such as roads and large canals. During routine monitoring, these leaves must be included in the sample taken. A good estimate of the population can be obtained by counting larvae only on the distal 40 pairs of leaflets in leaves around position 33 in the phylotaxy. Upon detecting an unusual increase in population on these leaves, the sampling can be extended to include leaf 25; again sampling the last 40 pairs of leaflets.

1. Improving soil physical conditions and nutrition of the crop. Drainage problems has to be corrected, as well as any nutritional unbalance.
2. Promoting growth of all plants that harbor natural enemies such as parasitoid wasps and flies. Cassia tora , Melanthera aspera , Scleria melaleuca , Senna stenocarpoides , Urena lobata and others should be protected and planted in sites where they do not interfere with normal agronomic practices within the plantation. Field personnel has to be trained so they can identify and protect these plants.
3. Discriminated weed control: manual weed control may spare some plants known to host natural enemies. Chemical control can also be done in bands, instead of blanket control
4. Pentatomid bugs and other predators, as well as some parasitoids can be mass reared and released.

1. When necessary, insecticides can be applied on localized foci, and using products and procedures that reduce the risk of causing damage to the environment. In oil palms, it has been argued that stem injection and root absorption of some insecticides may reduce the negative effects on parasitoids and predators.
2. Pesticide rotation: Bacillus thuringiensis formulations can be rotated with some piretroids, chitin inhibitors, etofenprox (Tebron) and others, B.t. (DIPEL 2L (0.5 - 0.8 kg/ha) has been used with good results.

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