Acrosternum arabicum Wagner (Hem: Pentatomidae) is one of the pests that is of great importance due to its qualitative and quantitative damage in pistachio orchards. Different diets have been used to breed this insect, but it has not been possible to keep this pest permanently in the laboratory. Previous studies showed that raw pistachio seeds also were a poor diet for this insect. In this research, using an artificial diet, the nutritional importance of the main substances in a conventional natural diet, sunflower seeds (Helianthus annuus) and peanut (Arachis hypogaea) was investigated.
Material and Methods
The primary colony was collected from the pistachio orchards of the central and suburbs of Rafsanjan city, and transferred as eggs to the laboratory. Green beans, peanuts, and sunflower seed kernels were used for its rearing. The eggs obtained from this colony were used in artificial diet experiments. The food ingredients used in the preparation of the artificial diet were wheat germ, wheat bran, Broad bean, peanut butter, and sunflower seed butter. In two-stage experiments, by changing the amounts of peanut butter and sunflower butter, life table parameters including intrinsic population growth rate, net population growth rate, nymph development time, and population doubling time were compared in a completely random design one-way analysis of variance (ANOVA) by the general linear model (GLM) procedure (SAS vol 9.5). After determining the role of sunflower seeds in A. arabicum nutrition, four other Pentatomidae bugs were reared on a sunflower seed-green bean diet and life table parameters were measured.
Result and Discussion
After the comparison of the life table and fecundity parameters it was found that by increasing the amount of sunflower butter in an artificial diet, the intrinsic rate of population increase (rm) changed significantly so that this index had a significant difference between D3 and D2 (p<0.0120), which had only sunflower seed and peanut butter respectively. In the second experiment with increasing sunflower butter in D4 and feeding on the conventional diet without peanut seeds, (rm) and the net reproductive rate (Ro), reached their highest value (0.111±0.006) and (114±17.253) in the case of the sunflower seeds-green bean diet respectively which showed significant difference with all diets (p<0.0001). It was found that among the available components, sunflower seeds are the most important nutritional substance, and other ingredients in the diet had no nutritional value for this insect. In addition, several other bugs can also be grown with the sunflower seed-green bean diet. The highest intrinsic rate of population increase (rr) and the highest survival rate of nymphs until maturity (IMS) were related to Peribalus sp., 0.123±0.011 and 0.886±0.042 respectively. The nymphs of the Sunnpest grew well and turned into adult insects by feeding on the sunflower seed-green bean diet so the immature survival rate (IMS) was 0.774±0.141 whereas previous results showed that immatures of this pest had a low survival rate when fed wheat grains (0.08-0.35). The physiology of nutrition in seed-feeding bugs may have some features that could affect the efficiency of digestion and absorption. These insects must first turn the contents of the dry seed into a thin suspension with the help of saliva and mechanical movements of the stylet so that it can be passed through the alimentary canal (which has a small diameter). The swallowed suspension is stored and re-condensed in the first part of the stomach. On the other hand, the adhesion of the primary suspension should be such that it does not prevent the operation of the pharyngeal pump. Because in natural conditions, Sunnpest nymphs feed on milky and pasty grains, dry wheat grains are probably not suitable food. The presence of gluten in dry grain and its dissolution in water creates networks consisting of protein fibers, which increases the viscosity of the initial suspension.
Results showed that the efficiency of non-artificial food for these bugs is much higher than artificial food. Therefore, in mass production programs, the use of artificial food is unjustified. By changing the containers or possibly mechanizing the breeding process, it is possible to increase the colony size, especially in the case of egg parasitoid mass rearing. This study also showed that sunflower seeds play an essential role in the rearing of these insects. The use of sunflower seeds in the rearing of the Sunnpest may facilitate the maintenance of this pest in the laboratory, which will lead to the development of research in this regard.