Ioan Rosca, Felicia Muresan,1 Angela Udrea,2 Marin Voicu,3 Valentin Brudea4 and Elena Bucurean5
Department of Plant Protection, Research Institute for Cereals and Industrial Crops, 8264 Fundulea, Romania
Abstract - The use of pheromone traps for monitoring the flight period of European corn borer, Ostrinia nubilalis, has been investigated. Trap captures with blends of (Z)- and (E)-11-tetradecen-1-yl acetate, at a ratio of 97:3 or 3:97, have shown that the Z-pherotype is predominant all over Romania. The traps attract also a number of other species, their specificity should be improved. Pheromone traps are a valuable tool to optimize the time of release of Trichogramma spp. or sterile males and will become an important component of integrated control programs.
Key words - European corn borer, Ostrinia nubilalis Hb., sex pheromone, monitoring, pest control, Romania
In Romania, the European corn borer, Ostrinia nubilalis, is considered to be the most important pest of maize after panicle apparition, being spread throughout the country. The damage caused by this pest on corn can reach up to 40% (Paulian et al. 1961). Multiannual data indicate averages of 44% plants attacked, resulting in a yield loss of 550 kg/ha or 7.5% (Paulian et al. 1976). O. nubilalis feeds also on hemp and sorghum crops, as well as other species of the wild flora.
The actual method to forecast European corn borer population levels consists of controlling, in at least three fields with different corn hybrids in each district, the number of attacked plants and the number of larvae per attacked plant. The warning system is also based on the registration of the flight period by light traps.
The sex pheromone of O. nubilalis consists of (Z)- and (E)-11-tetradecenyl acetate (Z11-14Ac, E11-14Ac) (Klun & Brindley 1970); the occurrence of pheromone strains, using predominantly either the Z- or E-isomer, has been studied in different parts of the world (Kochansky et al. 1975; McLeod et al. 1979; Stockel 1982; Roelofs et al. 1985).
A simple and efficient tool for monitoring of corn borer populations is a prerequisite for integrated pest management programs (Rosca et al. 1985, 1990, 1991), it has been investigated whether pheromone-baited traps could be used to this purpose.
From 1990 to 1995, the specificity and efficacy of synthetic sexual pheromone lures and traps produced by the Chemistry Institute (Cluj Napoca, Romania) has been studied. Pheromone traps, suspended 1 m above ground, separated by 50 m, were placed into corn fields. Lures were changed at two-week intervals, the sticky bottoms when it was necessary. The number of corn borers and of other lepidopteran species trapped was recorded weekly. Field tests were conducted from June to September.
With the development of an integrated management program in mind, corn borer dispersal and flight range was studied by release/recapture of marked males. Insects were marked by adding an emulsification mixture of Calco oil red N-1700 (150 mg/kg diet) and sunflower oil to the semisynthetic diet used for lab-rearing (Barbulescu & Rosca 1993). Lab-reared corn borer males were released in the field and recaptured with pheromone traps placed at various distances from the release sites, in the four cardinal directions. Traps were placed at 25, 100 and 200 m in 1993; at 100, 200 and 300 m in 1994; at 300, 600, 900, 1200 and 1500 m in 1995; and at 1000, 2000, 3000, 4000 and 5000 m in 1996.
The most efficient pheromone lures had been identified during preliminary studies from 1982 to 1987: The Z-lure contains a 97:3 blend of Z11-14Ac/E11-14Ac, the E-lure contains a 3:97 blend of these compounds and tetradecyl acetate (Rosca et al. 1991).
The results in Table 1 show the numbers of O. nubilalis males captured with the Z-lure throughout the trapping period. Trap catch varied between localities and years, most males were trapped at Turda, in 1992.
Figure Male flight of European corn borer populations in Romania, as monitored by Z-lures (a) and E-lures (b)
In addition, it has been shown for the first time that both the Z- and E-pherotypes of European corn borer occur all over Romania; before the E-type had not been recorded in the center and the north-east of the country (Rosca et al. 1991). Ostrinia nubilalis populations consist on the average of 92% Z-type and 8% E-type males, this ratio varies between years and localities (Table 2, Figure), but up to 14% E-males occurred in some fields.
| Locality | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 |
| Suceava | 1.75 | 1 | - | 19.5 | 45.5 | 5 |
| Podul Iloaiei | - a | 19 | 13.8 | 19 | 21.3 | 37.5 |
| Scuieni | 0.5 | - | 1.5 | 0.3 | 12 | 4 |
| Valu Traian | - | - | 13 | 17 | 32.3 | 104 |
| Fundulea | 8.3 | 14.8 | 23.3 | 29.5 | 35.3 | 17.2 |
| Oradea | 5 | 13.5 | 9.8 | 54.3 | 12.1 | 4 |
| Turda | 45 | 53 | 172 | 49.5 | 64.9 | 7.4 |
| a not detected | ||||||
| Pherotype | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 |
| E | 6.3 | 9.5 | 34.7 | 11.2 | 19.1 | 7 |
| Z | 60.5 | 101.3 | 233.3 | 189.1 | 223.4 | 179.1 |
The specificity of pheromone formulations is still not optimal, since other Microlepidoptera such as Tortrix viridana L., Etiella zinkenella Tr. and Emelia trabealis Scop. are frequently trapped. However, these species are easily distinguished from the target species.
The flight period of O. nubilalis, as monitored by pheromone traps is shown in the Figure. Our results indicate that there is even a small second generation at the end of August or early September.
Release and recapture experiments showed that the males did not fly further than 300 m/day under the local climatic conditions. The recapture rates were 5.9% in 1993, 3.9% in 1994, 0.2% in 1995 and 0.3% in 1996. Tests in 1995 and 1996 showed that the males did not travel further than 3000 m from the point of release.
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