Aging and Food Source Effects on Mandibular Stylets Teeth Wear of Phytophagous Stink Bug (Heteroptera: Pentatomidae)

Abstract

ABSTRACT -Studies were conducted to test the effect of age and food sources on wear of the mandibular teeth of the phytophagous pentatomid, Euschistus heros (F.). The total length (μm) of the area bearing the mandibular teeth, the length of the 1st tooth, and the height of the 2nd tooth for teneral (< 1 day-old) adults were signifi cantly greater than that of adults fed on natural [green bean, Phaseolus vulgaris pods, raw shelled peanuts, Arachis hypogaea, and mature soybean, Glycine max seeds] for 30 or 60 days. Adults fed on artifi cial dry diet showed, in general, similar results to those of teneral adults. Force (Newtons) required penetrating the natural foods was signifi cantly greater than that required penetrating the artifi cial diet. The greater hardness of the natural foods caused increased mandibular serration wear. KEY WORDS: Euschistus heros, mouthpart, morphology, penetration resistance, diet Insect feeding on tough plant parts often results in considerable wear of mandibles (Chapman 1995). Despite their highly sclerotized nature, which can be increased with the addition of zinc or manganese to the cuticle (Schofi eld et al 2002), this phenomenon does occur. Variable degrees of wear to the mandibles have been recorded in several insect groups with chewing mouthparts, such as grasshoppers Regarding insects with piercing/sucking mouthparts, little is know about the effect of food and/or age on the wear of mandibular stylets. The only report found is by To date, no study was made to measure mandibular wear of phytophagous stink bugs of different ages feeding on natural and artifi cial diets. To test this, we selected females of the pentatomid Euschistus heros (F.) of known ages, and offered them different types of food sources. We wanted to test the hypothesis that aging and tougher food source will increase mandibular wear. Material and Methods Insect colony. Adults of E. heros were fi eld-collected using a sweep on soybean, Glycine max cultivated at Embrapa Soja, in Londrina, PR, Brazil (latitude 23º 18' S) during October 2008. A colony was established in the laboratory. Bugs were fed on fresh green bean pods (Phaseolus vulgaris), raw shelled peanuts (Arachis hypogaea), and mature soybean seeds, which were replaced every two days. Pairs (n = 30) were placed in each of three clear plastic boxes (25 x 20 x 20 cm), and provided with the above mentioned foods. Boxes were kept in a walk-in chamber at 25 ± 1°C temperature, 65 ± 5% RH and a photoperiod of 14:10h (L:D). Food was replaced every other day and nymphs obtained were raised to adults. Cotton balls were offered as oviposition substrates Sample preparation and measurements taken. Less than 1 day-old (teneral) adult females of E. heros were selected from the laboratory established colony and were fed on natural diet (diet composed of the plant structures previously referred) for 30 (n = 5) and 60 days (n = 5), and on artifi cial diet (dry exposed diet -a square piece 0.5 cm was used