Data to the Biology of the Red Spotted Bug (Spilostethus [= Lygaeus] equestris L., Het., Lygaeidae) Causing the Achene Greening of Alimentary Cross-Bred Sunflower

Abstract

Western European, and especially German-based multinational food processing companies tend to have “alimentary purpose” sunflower hybrlds and varieties grown in Hungary. This “commercial” product is highly preferred as Substitute of walnuts, or as filling in chocolate, bread, other bakery products, or baked into the top layer thereof. In early 1990s German companies rejected several truckloads of export goods due to “greening of the seed in the achene”. Almost 90% of the rejected consignments originated from the Sandy ridge of the region between the rivers Danube and Tisza, which is severely infected with Asclepias syriaca L weed. Field investigations revealed unambiguously that the greening of the seed in the achene had been caused by the Spilostethus [= Lygaeus] equestris L plant bug. This species is able to cause extensive damages and discontinuities in the so-called Shoulder part of the achene with its powerful stinging-suctorial mouth organ. In the damaged area of intensive Chlorophyll formation begins due to the solar effect, which is the unambiguous cause of the greening of the seed in the achene. In our investigations the industrial purpose sunflower plantations in two neighbouring areas (Bacsalmas and Katymar) were studied in respect of the damage caused by the Spilostethus [= Lygaeus] equestris L. While in Bacsalmas (that district was less infected with the Asclepias syriaca L) we found a damage of decreasing intensity (8.85 damaged achenes per sunflower disc) as advancing towards the centre of the plantation, while in the area of Katymar (this area was severely infected with Asclepias syriaca L), this value was almost three times as high, reaching 31.71 damaged achenes per disc. Though the numbers are not very high in themselves -assuming that a well-built disc contains 1100 to 1200 seeds -, but the damage may result in significant fall of quality, or even prevent exporting. Our extensive research into the causes of the greening of the sunflower seeds made it clear that the Spilostethus [- Lygaeus] equestris L has a significant influence on the contents of the seeds it has damaged: it increases the proportion of linoleic acid (C18:2) by about 2.5 %. That affects the lasting quality of the achene unfavourably (HORVATH & BUJAKI, 1991). For this reason, a comprehensive study of the biology of the Spilostethus /= Lygaeus] equestris L became necessary for the developing possible protection methods. Such studies also represented the beginning of the investigation of any external or endogenous factors, that might obstruct the successful use of alimentary purpose sunflower hybrids or varieties in the food industry. According to GUNTHER (1975), the S. equestris L is indigenous from southern England to Siberia, and from central Sweden to the Mediterranean areas. It is less common north of Central Europe; it prefers areas with warmer climate. It likes staying both on the ground or in the flowers of various plants. It especially likes the tarne poison or swallowwort (Vincetoxicum officinale MNCH., syn.: Cynanchum vincetoxicum (L) PERS.). Data on the way of life of the S. equestris L in Hungary is extremely scarce, despite the fact that the species is widespread in our country. Information on its nourishing plants and habits can only be found in the publications of HORVATH (1984; 1986; 1987b; 1989; 1999) and BUJAKI & HORVATH (1992). Horvath (1984) inferred the nourishing plant specialization of the species from the total nitrogen contents of various plant seeds, such as those of the Asclepias syriaca L, and the sunflower (Helianthus annuus L). Amino-acid composition in the seeds of the A. syriaca is the most similar to that of the sunflower, soy or peanut. It may be assumed that its similarity to the sunflower seed is the cause of the fact that the S. equestris willingly sucks the ripening achenes of the sunflower, too. (HORVATH, 1984).