Modified environments

Heatorcoldcanbeusedtoeliminateoratleastslow the increase ofpopulations ofstored-productinsectpests. Ideal conditions for stored-productinsects are 25-32 °Cand 65-75% RH. Above and below this range insect growth and fitness are reduced, and in extreme conditions insects die. Most stored-product insects are killed when exposed to 40 °C for 24 h, 45 °C for 12 h, 50 °C for 5 min, 55 °Cfori min, or 60 °C for 30 s. Among the beetles, Lasiodema serricorne and Rhyzopertha dominica are highly tolerant of heat, while Sitophilus spp. and Tribolium castaneum are moderately tolerant. Acclimation to heat can occur. Brief exposures to 35-40 °Ccanincrease survival ofinsects to subsequent exposure to higher temperatures, butabove 55 °C there is little difference between acclimated and unacclimated individuals.

A temperature of —18 °C kills most stored product insects within 2-3 min. However, Sitophilus granarius can reproduce at 15 °C, and the rusty grain beetle, Cryptolestesferrugineus, can survive exposures to —12 °C after a 4-week acclimation at 15 °C. Exposure of Anobium eggs to —14 °C produces 99% mortality. Continuous exposure at —20 °C for 2-3 weeks is lethal to all stages of clothes moth species, carpet beetles, and other dermestids.

Exposure to —15 °C for 10 h is lethal to Pediculus spp. eggs, and exposure to —15 °C for 2 h is lethal to adult lice; exposure to —17 °C for 2 h is lethal to Cimex spp. adults. As temperatures approach 0 °C, the time required to kill many species increases to about 50 days. During a short exposure to a high temperature, some insects, especially those with a large body, are somewhat cooled by the water evaporating from their body. Hot and moist air reduces the amount of cooling by evaporation and is the most effective method of using heat. Hot air is lethal for Pediculus spp. eggs exposed to 50 °C for 0.5 h, and lethal to adults exposed to 46 °C for 1 h. Itis lethal to Cimex spp. eggs exposed to 45 °C for 1 h, and to adults exposed to 44 °C for i h. Cold temperatures have a similar effect on these two species.

Modified atmosphere generally refers to alteration of the gaseous environment in which an insect lives. Typically, it is produced artificially and maintained by enveloping an object or structure with a gas such as carbon dioxide or nitrogen. The source of the gas is usually a pressurized container, and it is important to maintain a nearly stable concentration. Application of modified atmospheres has been to control stored-food pests, and to remove insects from museum specimens, archival and library material. A high percentage of carbon dioxide coupled with limiting the oxygen concentration in the air space to i0-20% will kill insects in stored grain without damaging the product.

Temperature coupled with low levels of oxygen can control some insects. Food pests die within 30 days when exposed to low amounts of oxygen at 15 °C, and they die within 2-3 days at 30 °C. As exposure temperature increases from 32 to 43 °C in 99% nitrogen (low oxygen), the time required to kill all stages of the cigarette beetle, Lasioderma serricorne, decreases from 96 to 24 h. An oxygen level of 0.3% is lethal to Anthrenus museorum in about32 h, and lethal to Attagenus woodroffei and A. smirnovi in about 88 h. Lethal time for larvae of Anthrenus verbasci and Reesa vespulae is about 44 h, and for Trogoderma angustum it is about 57 h. Exposure of 7-14-days at 0.4% oxygen kills Tineola bisselliella, Lasioderma serricorne, Anthrenus vorax, and Stegobium paniceum.Forstructural pests, anatmosphereofi%oxygenkills old house borer and powderpost beetle adults within 20 days; however, they are notkilled at8o% carbon dioxide. The powder-post beetle, Lyctus brunneus,iskilled after a 7-14-day exposure at 0.4% oxygen. Exposure time necessary to produce death is generally decreased by raising the temperature, by adding 5% carbon dioxide, or by decreasing relative humidity (RH). In general, lethal time increases with increasing RH in atmospheres with a low percentage of oxygen. Exposure for 48 h in 0.32% oxygen and 33% RH provides 94% mortality of cigarette beetle larvae, but only 25% mortality at 75% RH. Increasing exposure temperature generally decreases lethal exposure time. The minimum exposure time of 45 min is required to kill the drywood termite Incisitermes minor and carpenter ant Camponotus vicinus at 48.9 °C and 49% RH.

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