Sesamia cretica
(greater sugarcane borer)

The geographical range of S. cretica includes most of the countries and islands of the Mediterranean basin and extends through the Middle East and Arabia to Pakistan, northern India and northern Africa, extending south to northern Kenya and northern Cameroon. According to Tams and Bowden (1953) this species does not extend westward of Cameroon; however, earlier records from Mali, Niger and Togo have again been included on the recently revised CABI/EPPO (2001) distribution map. This is a pest species linked to graminaceous crops with a preference for sorghum, maize and sugarcane. It is present on wild Gramineae with a preference for Panicum repens. S. cretica could extend its range following these crops/wild hosts and in correlation with climatic change. More studies on the distribution of this species are necessary. It belongs to the 'Sesamia' group of noctuids, a group of very similar species that are difficult to identify, and therefore misidentifications can occur regarding new distribution data.

The geographical range of S. cretica includes most of the countries and islands of the Mediterranean basin and extends through the Middle East and Arabia to Pakistan, northern India and northern Africa extending south to northern Kenya and northern Cameroon. According to Tams and Bowden (1953) this species does not extend westward of Cameroon; however, earlier records from Mali, Niger and Togo have been again included on the recently revised CABI/EPPO (2001) distribution map.

The country list includes records under the names Sesamia uniformis and S. griselda (CABI/EPPO, 2001).

Accidental introduction of this pest to new areas, as has already happened in Spain and southern France, would threaten production of graminaceous crops, especially maize, sorghum and sugarcane. S. cretica is listed as an A1 status quarantine pest for South-East Asia but there appear to be no records of interceptions or establishments within that region.

Recorded host plants of S. cretica are mainly graminaceous crops, especially cereals. Sorghum is often its main host; in Israel a decline in the incidence of S. cretica has been attributed to reductions in the area of sorghum during the 1970s (Melamed-Madjar and Tam, 1980). In Egypt S. cretica is a major pest of maize and sugarcane (Hafez et al., 1970). It has also been recorded on carnations in Egypt (Temerak, 1982a), but this record from a non-graminaceous host has not been authenticated by subsequent authors.

Ahmed (1980) made preliminary field observations on 11 species of grasses and cereal crops in the El-Serw region of Egypt and concluded that Panicum repens was the most favoured host plant for S. cretica, followed by maize.

Rivnay (1962) published details of the life cycle and seasonal cycle of S. cretica in Israel. A general account of its biology, based mainly on research in Egypt, was published by Salah (1977). A brief general summary of its biology in Europe was provided by Carter (1984).

Adults are nocturnal and females lay batches of 12 or more eggs under leaf sheaths of host plants. Young plants (such as seedling maize and sorghum) are most attractive during the first 2 weeks of growth, and become less attractive after they have developed seven or more leaves. Average adult life is 5-10 days, with females generally living longer than males.

Females lay about 10-12 egg batches, averaging 100-300 eggs each, over 3-4 nights. Eggs hatch after 4-8 days, depending on prevailing temperatures, and first-instar larvae crawl up into the leaf funnel to feed before tunnelling into the stems. During the growing season larvae generally feed for 4-6 weeks, during which they create galleries in the stems. They then pupate either within the bored stems or between the stems and the leaf sheaths: adults emerge 1-4 weeks later, depending on prevailing temperatures.

In southern Europe there are two generations per year, with peaks of adult activity in April-June and July-August. Further south there may be three or more generations and in Egypt up to four generations develop between mid-March and mid-September. Full-grown larvae of the last generation of the year overwinter within bored stems and complete their development early in the following growing season.

In Iraq, Younis et al. (1984) reported that S. cretica was continually present in maize fields from late March to November. There were five overlapping generations and larval, prepupal, pupal and adult stages averaged 11, 3.6, 9.5 and 3.6 days, respectively.

In Egypt, Temerak and Negm (1979) evaluated mortality factors on eggs and newly hatched larvae in natural populations on a susceptible and a relatively resistant sugarcane variety. They found that mortality by Telenomus sp. was the key factor during the egg stage, with about 74% parasitism on each of the varieties. Larval mortality of early instars was significantly higher on resistant varieties and predation during early larval development, especially by spiders, was considered to be a key mortality factor. Abdel-Wahab et al. (1987) studied field emergence of adults from early March and established that an average accumulation of 166, 433 and 601 day-degrees Celsius, based on an 11°C development threshold, was necessary for emergence of 10, 50 and 90% of the total overwintering population.

In the Sudan, El-Amin (1988) studied flight activity in sorghum and sugarcane fields by light trapping. Catches were highest during the winter (November-February) and were negatively correlated with average minimum temperatures. Host-preference tests showed that late-sown fodder sorghum and three varieties of grain sorghum were preferred to sugarcane. Monitoring of adult emergence from sorghum stalks indicated that they served as a reservoir for S. cretica in November-January that caused peak infestation of sugarcane.

Cayrol (1972) summarized the results of laboratory studies on the effects of different temperature regimes on larval and adult survival and longevity. All larvae died at temperatures below -15°C but exposure for 96 hours at -8°C caused a mortality of only 10%.

Natural enemies of S. cretica have been studied most intensively in Egypt since the late 1970s. The main parasitoids are egg parasites, especially Telenomus busseolae (Polaszek et al., 1993) and the larval ectoparasite Bracon brevicornis.

Hafez et al. (1977) studied the bionomics of T. busseolae in Egypt and observed that, although the eggs of many Lepidoptera were exposed to this parasitoid, only those of S. cretica were parasitized. Adults lived for 3-7 days and mated females laid about 40 eggs each. A small amount of superparasitism occurred but only one egg per host larva completed development. Up to 16 generations per year of T. busseolae were completed in the field at Giza (Egypt), compared with 4-5 generations of S. cretica, and this was considered to be the most important factor contributing to the effectiveness of T. busseolae against S. cretica. El-Kifl et al. (1977), also working in Egypt, published descriptions of eggs, third-instar larvae, prepupae and pupae of this species and determined development times at various temperatures in laboratory and field studies. At outdoor temperatures averaging 20.4°C the total period of development averaged 28.4 days, of which 24.1 days were spent in the pupal stage.

Polaszek et al. (1993) provided a taxonomic account of T. busseolae, recording it as widespread in Africa, present in Greece and occurring eastwards in Iran, Iraq and Israel. They recorded it as a parasitoid of various species of Sesamia and of Busseola fusca and Coniesta ignefusalis.

Temerak et al. (1980) studied the relative impact of B. brevicornis and its hyperparasite, Pediobius bruchicida on hibernating larvae of S. cretica in stacked sorghum stems in Egypt. Overall larval mortality was 14-68%, of which 5-28% was due to B. brevicornis. Hyperparasitism was indicated by cocoons turning black and was 100% towards the end of the winter. Temerak (1983d) studied the effects of venom injected by female B. brevicornis into S. cretica larvae to immobilize them and found that the number of completely paralysed larvae increased with the number of host larvae exposed to a single female in laboratory studies.

The same author has also studied other aspects of the biology of B. brevicornis, notably the effects of age, starvation and temperature on the envenomation of females (Temerak, 1983e); the suitability of five different lepidopterous hosts, of which S. cretica produced the largest females with the longest lifespan (Temerak, 1984c); the relationship between B. brevicornis and Serratia marcescens (Temerak, 1984a, b; Temerak, 1982a, b) and between B. brevicornis and Bacillus thuringiensis (Temerak, 1980); rearing techniques (Temerak, 1981; Temerak, 1983b, c); host preference and host sensitivity (Temerak, 1983a); factors affecting egg deposition (Temerak, 1984d); and host-habitat selection (Temerak, 1982c).

Predation on eggs and larvae was studied in Egypt by Temerak and Negm (1979). They reported that predation by ants and spiders was of minor importance as a factor in egg mortality (less than 2%, compared with 74% parasitism). Higher larval mortality (77-92%) was attributed mostly to predation, especially by spiders, on newly hatched larvae. Temerak (1978) published results of a preliminary survey of soil-inhabiting arthropods associated with pupae of S. cretica in sorghum fields in Egypt and reported predation by an earwig, Labidura riparia, an elaterid beetle, Lanelater notodonta, two species of ant, Paratrechina sp. and Pheidole sp., and a centipede, Lamyctes sp. Paratrechina sp. was considered to be the most abundant and active predator on S. cretica pupae in the soil.

Cayrol (1972) lists other parasitoids (mainly Hymenoptera), a pathogen, Beauvaria effusa, and records that sparrows (Passer domesticus) are predators on adults, but he does not give references.

Fediere et al. (1993) reported Sesamia cretica granulosis virus as a natural enemy of S. cretica.

Field infestations are easily detected by walking through crops looking for the symptoms (see Symptoms). Care must be taken to distinguish between dead hearts caused by shootflies (Atherigona spp.), chloropids and some plant pathogens, especially Fusarium. Identical symptoms are also caused by other species of stem borer and the presence of S. cretica is best confirmed by collecting larvae and pupae from damaged stems and rearing adults for identification by specialists.

Adults and immature stages resemble those of other species of Sesamia but adults can be positively identified on characters of the male and female genitalia described in Tams and Bowden (1953). In Spain, and in other areas where S. cretica occurs along with Sesamia nonagrioides, there is a possibility of confusion. Badolato (1976) compared the morphology of adult and immature stages of both species in detail and established diagnostic characters for the separation of larvae, pupae and adults.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

IPM Programmes

S. cretica is usually only one component of a complex of stem borers attacking graminaceous crops and IPM programmes will generally be targeted at the whole complex of species.

Chemical control is of limited use and the general trend is towards the use of non-chemical methods, including the development of host-plant resistance and the application of good cultural practices. This approach is most likely to be effective on sugarcane and on irrigated maize, but there is considerable potential for the implementation of IPM programmes on sorghum.

Cultural Control and Sanitary Methods

Salah (1977) discussed the destruction of maize stems and stools by chopping or burning after harvest to kill hibernating larvae and also noted that manipulation of planting dates to avoid first-generation attack had proved effective with maize and sugarcane.

In the Sudan, El-Amin (1988) concluded that infestations may be avoided or almost eliminated by early sowing of sorghum in July and early harvesting in late October.

Host-Plant Resistance

Selection for tolerance or resistance to lepidopterous stem borers in sugarcane, maize and sorghum may eventually be effective against S. cretica but there is little evidence of progress in the published literature. Field trials of seven varieties of sugarcane in Sudan indicated that at the tillering stage PR1000 was most susceptible to infestation and Co417 was most resistant, but at maturity M/165/38 was most susceptible and PR1000 was most resistant (El-Amin, 1984). Infestation, measured as percentage internodes bored, was positively correlated with stem thickness.

Biological Control

Classical biological control, involving the introduction of exotic natural enemies, has not been attempted yet and would require substantial research inputs before implementation. Conservation of indigenous natural enemies offers greater potential, as indicated by the research on parasitoids and predators (see Natural Enemies).

Chemical Control

Chemical control has been attempted in the past but has never been particularly successful against stem borers. Motorized spraying with carbaryl wettable powder has been used successfully but emulsifiable insecticides scorch young leaves (Salah, 1977).

Early Warning Systems/ Field Monitoring

Light-trapping of adults can be used to give early warning of adult activity, especially of the first generation, and field scouting for egg masses could be used to detect imminent infestations.

22/11/2007 Updated by:

Koen Maes, Consultant, Belgium