Relative susceptibility of Tribolium confusum life stages exposed to elevated temperatures

Methyl bromide, a space fumigant used in food-processing facilities, may be phased out in the United States by 2005. The use of elevated temperatures or heat treatment is gaining popularity as a methyl bromide alternative. During heat treatment, the temperature of the whole food-processing facility, or a portion of it, is raised and held between 50 and 60 degrees C for 24-36 h to kill stored-product insects. We determined time-mortality responses of the confused flour beetle, Tribolium confusum (Jacquelin du Val), eggs, young larvae, old larvae, pupae, and adults exposed to six constant temperatures between 46 and 60 degrees C. Responses of all five insect stages also were measured using exposure times of 160, 40, and 12 min at 46, 50, and 60 degrees C, respectively. Time-mortality responses of all T. confusum life stages increased with an increase in exposure time and temperature. Both time-mortality and fixed time responses showed eggs and young larvae to be most susceptible at elevated temperatures and old larvae to be least susceptible. Our results suggest that old larvae should be used as test insects to gauge heat treatment effectiveness, because heat treatment aimed at controlling old larvae should be able to control all other T. confusum life stages. Besides providing baseline data for successful use of heat treatments, time-mortality data collected at the six temperatures can be used for developing thermal death kinetic models for this species to predict mortality during actual facility heat treatments.     

Susceptibility of Lasioderma serricorne (Coleoptera: Anobiidae) life stages to elevated temperatures used during structural heat treatments

Heat treatment of food-processing facilities involves using elevated temperatures (50-60 degrees C for 24-36 h) for management of stored-product insects. Heat treatment is a viable alternative to the fumigant methyl bromide, which is phased out in the United States as of 2005 because of its adverse effects on the stratospheric ozone. Very little is known about responses of the cigarette beetle, Lasioderma serricorne (F.) (Coleoptera: Anobiidae), a pest associated with food-processing facilities, to elevated temperatures. Responses of L. serricorne life stages to elevated temperatures were evaluated to identify the most heat-tolerant stage. Exposure of eggs, young larvae, old larvae, and adults during heat treatment of a food-processing facility did not clearly show a life stage to be heat tolerant. In the laboratory, exposure of eggs, young larvae, old larvae, pupae, and adults at fixed times to 46, 50, and 54 degrees C and 22% RH indicated eggs to be the most heat-tolerant stage. Time-mortality responses at each of these three temperatures showed that the time for 99% mortality (LT99) based on egg hatchability and egg-to-adult emergence was not significantly different from one another at each temperature. Egg hatchability alone can be used to determine susceptibility to elevated temperatures between 46 and 54 degrees C. The LT99 based on egg hatchability and egg-to-adult emergence at 46 degrees C was 605 and 598 min, respectively, and it decreased to 190 and 166 min at 50 degrees C and 39 and 38 min at 54 degrees C. An exponential decay equation best described LT99 as a function of temperature for pooled data based on egg hatchability and egg-to-adult emergence. Our results suggest that during structural heat treatments eggs should be used in bioassays for gauging heat treatment effectiveness, because treatments aimed at controlling eggs should be able to control all other L. serricorne life stages.     

Reproductive performance of Tribolium castaneum (Coleoptera: Tenebrionidae) exposed to the minimum heat treatment temperature as pupae and adults

Managing stored-product insect pests by heating the ambient air of a food-processing facility to high temperatures (50-60 degrees C), also referred to as heat treatment, is an effective technology that has been used since the early 1900s. The minimum temperature during heat treatment for effective disinfestation is 50 degrees C. The effect of sublethal exposures to 50 degrees C on the reproductive performance of stored-product insects associated with food-processing facilities is unknown. The red flour beetle, Tribolium castaneum (Herbst), is a pest commonly found in food-processing facilities worldwide. The adverse effects on fecundity, egg-to-adult survival, and progeny production of T. castaneum exposed as 1-d-old pupae and 2-wk-old adults to 50 degrees C for 60 and 39 min, respectively, were determined in the laboratory. Pupae and adults exposed for the same time periods at 28 degrees C served as the control treatment. Four possible reciprocal crosses were carried out among adults from the heat-treated (50 degrees C) and control (28 degrees C) treatments. The number of eggs produced during the first 2 wk of adult life, survival of these eggs to adulthood, and adult progeny production after 2 and 8 wk of oviposition in treatments representing all four reciprocal crosses were determined. Fecundity, egg-to-adult survival, and adult progeny production decreased by 17-63, 52-63, and 66-78%, respectively, when males, females, and both males and females were exposed to 50 degrees C. These effects were relatively more pronounced in treatments in which pupae were exposed to the high temperature compared to adults, and in exposed females than in males. The impaired reproductive performance in T. castaneum pupae and adults surviving sublethal exposures to the minimum heat treatment temperature is valuable for understanding population rebound following a heat treatment intervention.     

Dynamic model for predicting survival of mature larvae of Tribolium confusum during facility heat treatments

Structural heat treatment, a viable alternative to methyl bromide fumigation, involves raising the ambient temperature of food-processing facilities between 50 and 60 degrees C by using gas, electric, or steam heaters, and holding these elevated temperatures for 24 h or longer to kill stored-product insects. A dynamic model was developed to predict survival of mature larvae, which is the most heat-tolerant stage of the confused flour beetle, Tribolium confusum (Jacquelin du Val), at elevated temperatures between 46 and 60 degrees C. The model is based on two nonlinear relationships: 1) logarithmic survival of T. confusum mature larvae as a function of time, and 2) logarithmic reduction in larval survival as a function of temperature. The dynamic model was validated with nine independent data sets collected during actual facility heat treatments conducted on two separate occasions at the Kansas State University pilot flour and feed mills. The rate of increase of temperature over time varied among the nine locations where mature larvae of T. confusum were exposed, and the approximate heating rates during the entire heat treatment ranged from 1.1 to 13.2 degrees C/h. The absolute deviation in the predicted number of larvae surviving the heat treatment was within 3-7% of the actual observed data. Comparison of the absolute deviation in the time taken for equivalent larval survival showed that the model predictions were within 2-6% of the observed data. The dynamic model can be used to predict survival of mature larvae of T. confusum during heat treatments of food-processing facilities based on time-dependent temperature profiles obtained at any given location.     

Susceptibility of Tribolium castaneum life stages exposed to elevated temperatures during heat treatments of a pilot flour mill: influence of sanitation, temperatures attained among mills floors, and costs

The influence of sanitation on responses of life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), was investigated in a pilot flour mill subjected to three, 24-h heat treatments by using forced-air gas heaters fueled by propane. Two sanitation levels, dusting of wheat flour and 2-cm-deep flour, were created in 25 plastic bioassay boxes, each holding eggs, young larvae, old larvae, pupae, and adults of T. castaneum plus two temperature sensors. Data loggers (48) were placed on the five mill floors to record air temperatures. The time required to reach 50 degrees C, time above 50 degrees C, and the maximum temperature among mill floors and in bioassay boxes were measured. The maximum temperature in bioassay boxes and in the mill was lower on the first floor than on other floors. This trend was apparent in time required to reach 50 degrees C and time above 50 degrees C, especially in compartments with 2-cm-deep flour. The mean +/- SE mortality of T. castaneum life stages on the first floor was 55.5 +/- 12.9-98.6 +/- 0.8%; it was 93.2 +/- 6.7-100 +/- 0.0% on other floors. Adults were the least susceptible stage. Mortality of T. castaneum stages in compartments with 2-cm-deep flour was generally lower than those with flour dust. Costs for the three heat treatments ranged from US$27,438 to $28,838. An effective heat treatment can be conducted within 24 h, provided temperatures on mill floors reach 50 degrees C in 8-12 h and are held above 50 degrees C for at least 10-14 h, with maximum temperatures held between 50 and 60 degrees C.     

Susceptibility of Plodia interpunctella (Lepidoptera: Pyralidae) developmental stages to high temperatures used during structural heat treatments

Heating the ambient air of a whole, or a portion of a food-processing facility to 50 to 60 degrees C and maintaining these elevated temperatures for 24 to 36 h, is an old technology, referred to as heat treatment. There is renewed interest in adopting heat treatments around the world as a viable insect control alternative to fumigation with methyl bromide. There is limited published information on responses of the Indian meal moth, Plodia interpunctella (Hübner), exposed to elevated temperatures typically used during heat treatments. Time-mortality relationships were determined for eggs, fifth-instars (wandering-phase larvae), pupae, and adults of P. interpunctella exposed to five constant temperatures between 44 and 52 degrees C. Mortality of each stage increased with increasing temperature and exposure time. In general, fifth-instars were the most heat-tolerant stage at all temperatures tested. Exposure for a minimum of 34 min at 50 degrees C was required to kill 99% of the fifth-instars. It is proposed that heat treatments aimed at controlling fifth-instars should be able to control all other stages of P. interpunctella.     

Thermal death kinetics of red flour beetle (Coleoptera: Tenebrionidae)

While developing radio frequency heat treatments for dried fruits and nuts, we used a heating block system developed by Washington State University to identify the most heat-tolerant life stage of red flour beetle, Tribolium castaneum (Herbst), and to determine its thermal death kinetics. Using a heating rate of 15 degrees C/min to approximate the rapid heating of radio frequency treatments, the relative heat tolerance of red flour beetle stages was found to be older larvae > pupae and adults > eggs and younger larvae. Lethal exposure times for temperatures of 48, 50, and 52 degrees C for the most heat-tolerant larval stage were estimated using a 0.5th order kinetic model. Exposures needed for 95% mortality at 48 degrees C were too long to be practical (67 min), but increasing treatment temperatures to 50 and 52 degrees C resulted in more useful exposure times of 8 and 1.3 min, respectively. Red flour beetle was more sensitive to changes in treatment temperature than previously studied moth species, resulting in red flour beetle being the most heat-tolerant species at 48 degrees C, but navel orangeworm, Amyelois transitella (Walker), being most heat tolerant at 50 and 52 degrees C. Consequently, efficacious treatments for navel orangeworm at 50-52 degrees C also would control red flour beetle.     

Impact of varying levels of sanitation on mortality of Tribolium castaneum eggs and adults during heat treatment of a pilot flour mill

The influence of sanitation on responses of life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), an economically important pest in flour mills, was investigated in a pilot flour mill subjected to two, 24-h heat treatments. One hundred eggs or 100 adults of T. castaneum were exposed inside each 20-cm diameter by 15-cm high PVC rings holding 0.1-, 0.2-, 1.0-, 3.0-, 6.0-, and 10.0-cm-deep wheat flour to simulate different sanitation levels that may exist in a flour mill. These rings were placed on the first and third floors of a pilot flour mill. On the first floor, temperatures inside rings with eggs reached 50 degrees C in 7-11 h only in 0.1- and 0.2-cm-deep flour treatments. In all other treatments the maximum temperatures attained generally were below 50 degrees C and inversely related to flour depth. Adults of T. castaneum on this floor were less susceptible than eggs. The egg mortality decreased linearly with an increase in flour depth, whereas that of adults decreased exponentially. All eggs and adults in rings on the third floor were killed irrespective of flour depth, because temperatures inside rings reached 50 degrees C in 15-17 h and were held above 50 degrees C for 6-8 h with the maximum temperatures ranging between 55.0 and 57.0 degrees C. Although the protective effects of flour on survival of T. castaneum eggs and adults were evident only if temperatures did not reach 50 degrees C, removal of flour accumulations is essential to improve heat treatment effectiveness.     

Effects of temperature and exposure time on mortality of stored-product insects exposed to low pressure.

The prospects of using low pressure that creates a low-oxygen atmosphere to control stored-product insects were investigated in the laboratory. Eggs, larvae, and pupae of Tribolium castaneum (Herbst), Plodia interpunctella (Hübner), and Rhyzopertha dominica (F.) were exposed to 32.5 mmHg in glass chambers at 25, 33, 37, and 40 degrees C for times ranging from 30 min to 144 h. Time-mortality data were subjected to probit analyses and lethal dose ratios were computed to determine differences in lethal time (LT) values among all species-life stage combinations across the four temperatures. Eggs of each species were the life stage most tolerant to low pressure. Pupae of T. castaneum and R. dominica were more tolerant to low pressure than larvae. In all life stages, mortality increased with increasing exposure time to low pressure and also with increasing temperature. Immature stages of R. dominica were more tolerant to low pressure than immature stages of the other two species. The LT99 for R. dominica eggs was 176.32 h at 25 degrees C and that for P. interpunctella eggs was 28.35 h at the same temperature. An increase in temperature to 33 degrees C resulted in a LT99 < of 85.98 h for R. dominica and 6.21 h for P. interpunctella. Higher temperatures resulted in further significant reduction in lethal time values. Low pressure represents a simple, nonchemical alternative to fumigants such as methyl bromide and phosphine for controlling pests of stored-products or other commodities.     

Thermal death kinetics of fifth-instar Plodia interpunctella (Lepidoptera: Pyralidae)

Heat treatments have been suggested as alternatives to chemical fumigants for control of postharvest insects in dried fruits and nuts. Conventional forced hot air treatments heat product too slowly to be practical, but radio frequency treatments are capable of more rapid product heating. While developing radio frequency heat treatments for dried fruits and nuts, the heat tolerance of nondiapausing and diapausing fifth-instar larvae of the Indianmeal moth, Plodia interpunctella (Hübner), was determined using a heating block system developed by Washington State University. Both a 0.5th order kinetic model and a classical empirical model were used to estimate lethal exposure times for temperatures of 44-52 degrees C for nondiapausing fifth-instar larvae. We obtained 95% mortality at exposures suitable for practical radio frequency treatments (< or = 5 min) with temperatures of 50 and 52 degrees C. Diapausing larvae were significantly more tolerant than nondiapausing larvae at the lowest treatment temperature and shortest exposure, but differences were not significant at more extreme temperature-time combinations. Previous studies showed that fifth-instar larvae of the navel orangeworm, Amyelois transitella (Walker), were more heat tolerant than either diapausing or nondiapausing Indianmeal moth larvae. Consequently, efficacious treatments for navel orangeworm would also control Indianmeal moth.     

Susceptibility of Tribolium castaneum (Coleoptera: Tenebrionidae) life stages to flameless catalytic infrared radiation

The susceptibility of various life stages of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), a pest of stored wheat, Triticum aestivum L., to flameless catalytic infrared radiation in the 3-7-microm range was evaluated in the laboratory. Immature stages were collected from flour infested with T. castaneum adults only for 1 d. Stages collected after 1 d represented eggs (collected on day 0); those collected after 7, 14, and 21 d from day 0 represented larvae in different developmental stages, whereas those collected after 24 d represented pupae. Adults (2 wk old) were collected after 42 d. Each of these stages was exposed for 45 or 60 s in 113.5 or 227.0 g of wheat at a distance of 8.0 or 12.7 cm from a bench top infrared emitter. The mean temperatures attained during exposures were measured continuously using a noncontact infrared thermometer connected to a computer. The mean grain temperatures attained increased with an increase in exposure time and were inversely related to distance from the emitter. Grain quantity least influenced mean temperatures attained. Pupae were the least susceptible stage and larvae collected after 7 d were the most susceptible stage. Variation in probability of death of various life stages decreased with an increase in mean grain temperatures attained. All life stages were killed after a 60-s exposure at a distance of 8.0 cm from the emitter in 113.5 g of wheat, where the mean +/- SE temperatures attained ranged from 107.6 +/- 1.2 to 111.4 +/- 0.5 degrees C. Our laboratory results using small grain quantities and short exposure times showed that flameless catalytic infrared radiation can be a valuable tool for managing insects in stored organic and nonorganic wheat.     

Residual efficacy of methoprene for control of Tribolium castaneum (Coleoptera: Tenebrionidae) larvae at different temperatures on varnished wood, concrete, and wheat

The residual efficacy of the juvenile hormone analog methoprene (Diacon II) was evaluated in bioassays using larvae of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) exposed on unsealed concrete or varnished wood treated with a liquid formulation and held at different temperatures. When these two types of surfaces were stored at 20, 30 or 35 degrees C for 0-24 wk, the percentage of adult emergence on concrete increased with time. In contrast, there was no adult emergence from larvae exposed to varnished wood at 24 wk after treatment at any of these temperatures. The presence of flour reduced residual efficacy of methoprene on concrete, but not on varnished wood, with no differences between cleaning frequencies. Methoprene was also stable for 48 h on concrete held at 65 degrees C and wheat, Triticum aestivum L., held at 46 degrees C. Results show that methoprene is stable at a range of temperatures commonly encountered in indoor food storage facilities and at high temperatures attained during insecticidal heat treatments of structures. The residual persistence of methoprene applied to different surface substrates may be affected more by the substrate than by temperature.     

Effect of high and low temperatures on the drugstore beetle (Coleoptera: Anobiidae)

The drugstore beetle, Stegobium paniceum (L.) (Coleoptera: Anobiidae), is a pest of stored medicinal and aromatic plants. Generally, mortality of each stage increased with an increase of temperature and exposure time. Heat tolerance for different stages from highest to lowest was young larvae, old larvae, eggs, adult, and pupae. The mortality after 7 h at 42 degrees C for young larvae, old larvae, eggs, adults, and pupae, respectively, was 16 +/- 5, 31 +/- 6, 48 +/- 3, 63 +/- 8, and 86 +/- 2% (mean +/- SEM). Similar trends for stage specific mortality were seen with the lethal time for 90% mortality (LT90) at 42 degrees C; 773, 144, 12, and 11 h for old larvae, eggs, adults, and pupa respectively. Mortality was too low with young larvae to estimate LT90. The LT90 for young larvae at 42, 45, 50, 55, and 60 degrees C was 25, 20, 3.9, 0.18, and 0.08 h, respectively. The cold tolerance of different stages at 0 degree C from highest to lowest was adults, old larvae, young larvae, pupae, and eggs. The LT90 at 0 degrees C was 298, 153, 151, 89, and 53 h, respectively. The LT90 for adults at 5, -5, -10, and -15 degrees C was 792, 58, 2, and 0.8 h, respectively. The supercooling point of adults was -15.2 +/- 2 degrees C; young larvae, -9.0 +/- 0.8 degrees C; old larvae, -6.5 +/- 0.5 degrees C; and pupae, -4.0 +/- 1.4 degrees C. Heat treatments that control young larvae should control all other stages of S. paniceum. Cold treatments that control adults should control all other stages of S. paniceum. Dried plants stored at 5 degrees C for 45 d or 42 degrees C for 30 h and then kept below 18 degrees C throughout the rest of the year, should remain pest-free without any chemical control.     

Determination of mortality of different life stages of Tribolium castaneum (Coleoptera: Tenebrionidae) in stored barley using microwaves

Barley, Hordeum vulgare L., one of the important crops in Canada, is used in malting, feed, and food industries. Disinfestation of barley using microwaves can be an alternative to chemical methods used to kill insects. A pilot-scale industrial microwave system operating at 2.45 MHz was used in this study to determine the mortality of life stages (egg, larva, pupa, and adult) of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Barley samples of 50 g each at 14, 16, and 18% moisture content (MC; wet basis) were infested with various life stages of T. castaneum and exposed to microwave energy at different power levels and exposure times, and the mortality of the insects was determined. The average temperature of the 14% MC sample exposed to 28 s at 0, 200, 300, 400, and 500 W were 27.4, 42.6, 53.7, 66.9, and 73.0 degrees C, respectively, and those exposed to 56 s at 0, 200, 300, and 400 W were 27.4, 57.3, 75.5, and 91.2 degrees C, respectively. A similar range of temperature was observed for 16 and 18% MC barley. Complete mortality of all life stages of T. castaneum can be achieved at a power level of 400 W and an exposure time of 56 s or at 500 W for 28 s. Among the life stages of T. castaneum, eggs were the most susceptible to microwave energy and adults were the least susceptible. There was no significant difference in the mortality of larvae and adults at 14, 16, and 18% MC, but the mortality was significantly different for eggs and pupae at different MCs. There was a significant increase in the mortality with an increase in power level or exposure time or both. Germination capacity of the seeds was decreased with an increase in power level or exposure time or both. Quality characteristics such as alpha-amylase, diastatic power, soluble protein, viscosity, and density of the barley malt treated at 500 W for 28 s were same as the control sample, whereas the samples treated at 400 W for 56 s were significantly lower.     

Toxicity of propylene oxide at low pressure against life stages of four species of stored product insects

The relative toxicity of propylene oxide (PPO) at a low pressure of 100 mm Hg to four species of stored product insect at 30 degrees C over a 4-h exposure period was investigated. PPO at 100 mm Hg was toxic to all four species tested: Tribolium castaneum (Herbst), Plodia interpunctella (Hübner), Ephestia cautella (Wlk.), and Oryzaephilus surinamensis (L.). There were differences in susceptibility between the life stages of the tested insect species. Mortality tests on all life stages of the insects resulted in LD99 values ranging from 4.7 to 26.1 mg/liter. The pupal stage of E. cautella, O. surinamensis, and T. castaneum was the most tolerant stage with LD99 values of 14.4, 26.1, and 25.7 mg/liter, respectively. For P. interpunctella, the egg stage was most tolerant, with a LD99 value of 15.3 mg/liter. Generally, PPO at 100 mm Hg was more toxic to P. interpunctella and E. cautella than to O. surinamensis and T. castaneum. A 99% mortality of all life stages of the tested species was achieved at a concentrations x time product of 104.4 mg h/liter. These findings indicate that a combination of PPO with low pressure can render the fumigant a potential alternative to methyl bromide for rapid disinfestation of commodities.     

Relationship between population growth of the red flour beetle Tribolium castaneum and protein and carbohydrate content in flour and starch

The effects of eight diets (atta flour, wheat flour, self-rising flour, rice flour, custard powder, corn flour, tapioca starch, and potato starch) on the development of the red flour beetle, Tribolium castaneum (Herbst), reared at 29-31 degrees C and 66-70% RH were assessed. Five pairs of male and female T. castaneum were reared on the respective diets for 28 d before the experimental setup was dismantled and adult counts were recorded. In another experiment, the insects were allowed to mate and oviposit in each flour or starch type over a period of 7 d before being removed. The counting of pupae and adult emergence began on the day of emergence and was continued on a daily basis until day 140. Proximate analysis was performed for chemical composition of each diet, and the numbers of new adults that developed were found to be positively correlated (r2 = 0.97; P < 0.05) with the protein content and negatively correlated (r2 = 0.93; P < 0.05) with the carbohydrate content. For T. castaneum, the suitable diets were ranked as follows: atta flour > wheat flour > self-rising flour > rice flour > custard powder > corn flour > tapioca starch > potato starch. T. castaneum larval development to the pupal and adult stages developed significantly faster in atta flour (P < 0.05) than in the other diets, and the greatest number of progeny was produced from beetles reared on atta flour. Fewer adults emerged from wheat flour, self-rising flour, and rice flour, and no new emergences were recorded for the remaining diets. Developmental rate was much slower in beetles reared on diets in which a low number in progeny was produced. These data illustrate that different diets can influence the sustainability of these insects and affect their development and growth.     

Generic vapor heat treatments to control Maconellicoccus hirsutus (Homoptera: Pseudococcidae)

Vapor heat treatments were developed against life stages of the mealybug Maconellicoccus hirsutus (Green) (Homoptera: Pseudococcidae). Treatments tested were 47 degrees C for 5-50 min in 5-min increments and 49 degrees C for 3, 5, 8, 10, and 12 min. All tests were conducted with mixed age M. hirsutus on Chinese pea, Pisum sativum L. Treatment at 47 degrees C required 45 min to kill all M. hirsutus, whereas treatment at 49 degrees C required 10 min. The adult female and nymphal stages were the most heat tolerant at 47 degrees C, but the egg stage was the most heat tolerant at 49 degrees C. Use of the vapor heat treatments on other commodities will require achieving or exceeding the proper temperature and duration at all locations on the host where M. hirsutus may reside.     

Carry‐over effects of multiple stressors on benthic embryos are mediated by larval exposure to elevated UVB and temperature

Damaging effects of UVB in conjunction with other stressors associated with global change are well‐established, with many studies focused on vulnerable early life stages and immediate effects (e.g., mortality, developmental abnormalities). However, for organisms with complex life cycles, experiences at one life stage can have carry‐over effects on later life stages, such that sublethal effects may mediate later vulnerability to further stress. Here, we exposed embryos in benthic egg masses of the New Zealand intertidal gastropod Siphonaria australis to treatments of either periodic stress (e.g., elevated UVB, salinity, and water temperature mimicking tidepool conditions in which egg masses are commonly found during summer) or control conditions (low UVB, ambient salinity, and water temperatures). Although there was high mortality from stressed egg masses, 24% of larvae hatched successfully. We then exposed the hatching larvae from both egg mass treatments to different combinations of water temperature (15 or 20 °C) and light (high UVB or shade) 12 h per day for 10 days. The most stressful larval conditions of 20 °C/high UVB resulted in low survival and stunted growth. Carry‐over effects on survival were apparent for shaded larvae exposed to elevated temperature, where those from stressed egg masses had 1.8× higher mortality than those from control egg masses. Shaded larvae were also larger and had longer velar cilia if they were from control egg masses, independent of larval temperature. These results demonstrate that previous experience of environmental stress can influence vulnerability of later life stages to further stress, and that focus on a single life stage will underestimate cumulative effects of agents of global change.     

The ontogeny of physiological response to temperature in early stage spiny lobster (Jasus edwardsii) larvae

The physiological response to temperature, in terms of oxygen consumption, nitrogen excretion and feed intake was examined in Jasus edwardsii larvae at mid-stages I-III. From stage I to stage III, the mass-specific oxygen consumption increased in a sigmoid pattern over the temperature range of 10-22 degrees C. The Q(10) value declined significantly from 14-18 to 18-22 degrees C range, indicating a reduced temperature dependence of larval metabolism at higher temperatures. At all stages, feed intake increased with increasing temperature but reached a plateau at the higher temperatures for stages I and II larvae. In contrast, nitrogen excretion increased linearly over this temperature range for all larval stages. Therefore, higher temperatures ( approximately 22 degrees C) may cause an energetic imbalance and reduce growth potential in early stage larvae. While the convection requirement index (quotient of feed intake and oxygen consumption) indicated an equivalent metabolic feeding efficiency from 14 to 22 degrees C, a consistent decline of the O/N ratio above 16-18 degrees C from stage I to stage III suggested that exposure to elevated temperatures may result in an increase in the amount of protein being diverted from growth to catabolic processes. Based on these results, a temperature of 18 degrees C is recommended for the culture of early stage J. edwardsii larvae.