Evaluating Penetration Ability of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) Larvae into Multilayer Polypropylene Packages
The larvae of the Indian meal moth, Plodia interpunctella (Hübner), can invade or penetrate packaging materials and infest food products. Energy bars with three polypropylene packaging types were challenged with eggs (first instars), third instars, and fifth instars of P. interpunctella to determine package resistance at 28 °C and 65% r.h. The packing types were also challenged with two male and two female pupae of P. interpunctella under similar conditions in order to determine which package provided the greatest protection against larval penetration. Samples infested with eggs, third instars, and pupae were evaluated after 21 days and 42 days to count the number of larvae, pupae, and adults found inside the packages. Packages challenged with fifth instars were observed after 21 days to count the number of larvae, pupae, and adults inside each package. The number and diameter of the holes were determined in each package, followed by the amount of damage sustained to the energy bar. Third and fifth instars showed a higher tendency to penetrate all of the packaging types. First instars showed a reduction in package penetration ability compared with third and fifth instars. The increase in exposure time resulted in an increase in the damage sustained to the energy bars. Among packaging types, the thickest package (Test A) was most resilient to penetration by all of the larval stages. In conclusion, energy bar manufacturers need to invest more effort into improving packaging designs, creating thicker gauge films, or advancing odor barrier technology, in order to prevent penetration and infestation by P. interpunctella larvae.
Barrier property and penetration traces in packaging films against Plodia interpunctella (Hübner) larvae and Tribolium castaneum (Herbst) adults
The barrier property of different types of plastic film (with or without pinholes) against two insects, Plodia interpunctella (Hubner) larvae and Tribolium castaneum (Herbst) adults, and the morphology of damage produced in these insects were investigated. Using a penetration apparatus, four types of plastic films varying in thickness were used for insect-penetration tests: casted polypropylene, 20 μm and 25 μm (CPP20 and CPP25); oriented polypropylene, 20 μm and 30 μm (OPP20 and OPP30); linear low-density polyethylene, 40 μm and 50 μm (LLDPE40 and LLDPE50); and polyethylene terephthalate 12 μm and 16 μm (PET12 and PET16). After being fixed and tested in the penetration apparatus, each film was cut into a disc shape and 10 holes (200 μm diameter) were made by a pin. The shape of film damage and the mouthparts of insects were observed using scanning electronic microscopy. Plodia interpunctella larvae could penetrate all films with pinholes, while T. castaneum adults were unable to penetrate any of the films tested, even those with pinholes. The penetration-percentages by P. interpunctella larvae were 38% (LLDPE40), 3% (LLDPE), 53% (CPP20), 37% (CPP25), 63% (OPP20), 43% (OPP30), 83% (PET12) and 63% (PET16). The elongation value, tensile strength and thickness of film were important factors in the penetration test. LLDPE, which has the highest elongation value and the lowest tensile strength value, was the film that best protected against insect penetration. In CPP and LLDPE films, there were many scratches and tears around the holes. In comparison, much less damage was observed around the holes in OPP and PET films. By observing the mouthparts of insects, it was determined that P. interpunctella larvae had sharper mandibles than those of T. castaneum adults.
Inhibition of Root Growth and Polyamine Metabolism in Sunflower (Helianthus annuus) Seedlings Under Cadmium and Copper Stress
Although sunflower is usually regarded as a highly tolerant crop, impairment of root growth at initial stages of plant development may result in poor crop establishment and higher susceptibility to pathogen attack. In order to evaluate if Cd2+ and Cu2+ may impact on sunflower germination and initial root development, a pot experiment under controlled conditions was carried out. Possible involvement of polyamine metabolism in sunflower response to these stressors was also investigated. Although Cd2+ and Cu2+ treatments affect neither seed germination nor radicle emergence, sunflower seedlings grown in the presence of these heavy metals showed significant inhibition of root growth, being this inhibition greater for Cd2+. Both metals caused significant increases in proline contents at the highest concentrations tested (0.5 and 1 mM), and these increments were more pronounced for Cd2+ treatments, especially between days 3 and 10. Metals also increased putrescine (Put) contents at all concentrations assayed from the seventh day onward, causing no variations on this polyamine time-course pattern. Spermine and spermidine contents, however, were increased only by 1 mM Cd2+. Arginine decarboxylase seems to have been the enzyme responsible for Put increases under both metal treatments. This work demonstrates that initial root growth of sunflower seedlings may be significantly impaired in Cd2+ or Cu2+ contaminated soils. It also shows that polyamines are key biological compounds, which are probably involved in signaling pathways triggered under stress environmental conditions.