Effects of methyl bromide concentration, fumigation time, and fumigation temperature on Mediterranean and oriental fruit fly (Diptera: Tephritidae) egg and larval survival

The effects of methyl bromide (MB) concentration (16, 32,48, or 64 g/m3), fumigation temperature (15, 20, 25, or 30 degrees C), and fumigation time interactions on the survival of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), and oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), eggs and first and third instars were recorded. Increasing the fumigation temperature from 15 to 20 degrees C or from 20 to 25 degrees C resulted in a significant reduction in fumigation time required for equivalent egg and larval mortalities at all studied MB concentrations; no further reductions in fumigation time resulted from increasing the temperature from 25 to 30 degrees C. Conversely, increasing temperature and time allowed for a reduction in MB concentration to obtain equivalent mortality. Thus, the optimum fumigation temperature for Mediterranean and oriental fruit fly eggs and larvae was 25 degrees C. Reducing MB concentrations required for phytosanitary fumigations would save time and expense, and reduce the amount of MB released into the atmosphere during aeration. Mediterranean fruit fly was as or more tolerant to MB than oriental fruit fly in MB tolerance for eggs and first instars. The egg stage was generally more tolerant to MB regardless of concentration. However, Mediterranean fruit fly eggs showed similar tolerance to first instars at 25 degrees C for the three highest concentrations and to third instars at 25 and 30 degrees C for the highest concentration, with no significant difference between them. Therefore, eggs alone can be used to obtain MB fumigation efficacy and quarantine security data at fumigation temperatures between 15 and 30 degrees C for Mediterranean and oriental fruit fly.     

Reaction orders for thermal mortality of third instars of Mexican fruit fly (Diptera: Tephritidae)

Mexican fruit fly, Anastrepha ludens (Loew), is a quarantine pest of several fruit, including citrus, avocados, and mangoes, from extreme southern Texas to Costa Rica. To provide information for modeling heat phytosanitary treatments, third instars were heated with an aluminum heating block between 44 and 50 degrees C for time intervals up to those causing 100% mortality. At 44 and 50 degrees C, 100% mortality was achieved at 100 and 2 min, respectively. Each 2 degrees C increase in temperature resulted in a three-fourths reduction in the amount of time required to achieve 100% mortality. Mortality was modeled using thermal death kinetics, and the most suitable reaction order was the 0.5th. The thermal death activation energy was 560.7 kJ/mol, which is very similar to the value found for Mediterranean fruit fly, Ceratitis capitata (Wiedemann), in a previous study, indicating similar modes of action for heat mortality. However, the Mexican fruit fly had a lower threshold for heat-induced mortality, resulting in less time at all temperatures studied to achieve 100% mortality compared with the Mediterranean fruit fly. This type of information being gathered for fruit flies could lead to the development of generic phytosanitary heat treatments, which are available for other major phytosanitary treatments, such as cold storage, methyl bromide fumigation, and ionizing irradiation.     

Thermal responses of oriental fruit fly (Diptera: Tephritidae) late third instars: mortality, puparial morphology, and adult emergence

Responses of late third instars of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), to high temperatures (43, 46, and 48 degrees C) were investigated. The different heat exposures not only affected the timing of death but also induced different quantities of malformed puparia and changed the average eclosion time. A majority of larvae died immediately (as larvae) after 30 min at 46 degrees C and > or =15 min at 48 degrees C, whereas most individuals died as pupae after 10-25 min of 46 degrees C, 5-10 min of 48 degrees C, and 40-60 min of 43 degrees C treatments. Lethal times estimated by immediate mortality were longer than those estimated by delayed mortality at the same high temperature. Surviving larvae formed four types of puparial morphology (normal, bottlenose, larviform, and peanut form). The percentage of normal puparia showed a negative correlation with exposure time at all test temperatures. The number of bottlenose was more than the larviform and the peanut at 46 degrees C for < or =20 min and at 48 degrees C for < or =10 min, respectively, whereas the number of larviform was more than the bottlenose and the peanut at 46 degrees C and 48 degrees C for longer exposure times. The average eclosion time increased at first, then decreased as the exposure time prolonged, and the longest average eclosion time occurred in the 40-min exposure at 43 degrees C, 15-min exposure at 46 degrees C, and 10-min exposure at 48 degrees C.     

Hot-water immersion quarantine treatment against Mediterranean fruit fly and Oriental fruit fly (Diptera: Tephritidae) eggs and larvae in litchi and longan fruit exported from Hawaii

Immersion of litchi fruit in 49 degrees C water for 20 min followed by hydrocooling in ambient (24 +/- 4 degrees C) temperature water for 20 min was tested as a quarantine treatment against potential infestations of Mediterranean fruit fly, Ceratitis capitata (Wiedemann); and oriental fruit fly, Bactrocera dorsalis Hendel, eggs or larvae in Hawaiian litchi, Litchi chinensis Sonnerat. The 49 degrees C hot-water immersion of litchi provided probit 9 (99.9968% mortality with >95% confidence) quarantine security against eggs and first instars. There were no survivors from 15,000 each feeding and nonfeeding Mediterranean fruit fly or oriental fruit fly third instars immersed in a computer-controlled water bath that simulated the litchi seed-surface temperature profile during the 49 degrees C hot-water immersion treatment. Litchi served as the model for longan, Dimocarpus longan Lour., a closely related fruit that is smaller and also has commercial potential for Hawaii. Modified fruit infestation and holding techniques used to obtain adequate estimated treated populations from poor host fruit, such as litchi and longan, are described. Data from these experiments were used to obtain approval of a hot-water immersion quarantine treatment against fruit flies for litchi and longan exported from Hawaii to the U.S. mainland.     

Population growth and development of psocid Lepinotus reticulatus at constant temperatures and relative humidities

We investigated the effects of temperature and relative humidity on population growth and development of the psocid Lepinotus reticulatus Enderlein. Part of this study assessed the effects of marking psocids by using methylene blue, chalk powder, and fluorescent powder to differentiate nymphal stages during development. We found that marking psocids by using methylene blue increased mortality and took twice as long to accomplish compared with marking by using fluorescent powder. Using chalk powder shortened the duration of third and fourth nymphal instars. Marking psocids by using fluorescent powder had no effect on mortality or duration of nymphal instars. Therefore, we recommend using fluorescent powder for marking psocids. L. reticulatus did not survive at 32, 43, and 55% RH, whereas populations increased from 22.5 to 32.5 degrees C at 75% RH. The largest population growth was recorded at 30 and 32.5 degrees C, whereas only 9% of nymphs developed to adults and populations declined at 35 degrees C. We developed temperature-dependent developmental equations for eggs, individual nymphal, combined nymphal, and combined immature stages. These equations showed predicted optimal temperatures for the development of eggs, combined nymphal, and combined immature stages to be 32.3, 34.5, and 34.4 degrees C, respectively; development at these temperatures was completed in 6.3, 16.7, and 23.3 d, respectively. Our study shows that psocids that consume their exuviae develop faster than those that do not, and this effect is more pronounced at lower temperatures. These data give us better understanding of L. reticulatus population dynamics, and they can be used to develop effective management strategies for this psocid.     

Toxicity,persistence, and efficacy of indoxacarb on cabbage looper (Lepidoptera: Noctuidae) on cabbage

Toxicity of indoxacarb was bioassayed against eggs and young (first and second instars) and older larvae (third and fourth instars) of cabbage looper, Trichoplusia ni (Hübner), on cabbage (Brassicae oleracea variety capitata L.), and persistence of field-aged leaf residues of indoxacarb was bioassayed with second and third instars of T. ni on cabbage. Efficacies of indoxacarb and several other newer insecticides to T. ni were tested under field conditions for two seasons in south Texas. LC50 and LC90 values for T. ni eggs were relatively high, indicating that indoxacarb has little ovicidal effects on T. ni eggs. Indoxacarb was highly toxic to T. ni larvae, having low LC50 and LC90 values. Bioassays of field-aged leaf residues of indoxacarb tested in the spring of 1998 (0-, 3-, 5-, and 12-d-old residues) and the fall of 2000 (0-, 3-, 5-, 7-, 9-, and 13-d-old residues) indicated that ingesting indoxacarb was highly toxic to the second and third instars of T. ni, giving 100% mortality for the second instars at 2 d after exposure, and 100% mortality for third instars at 5 d after exposure. Two trials conducted under field conditions show that indoxacarb at 0.072 g (AI) /ha rate was effective against T. ni in cabbage, providing marketable cabbage with three applications per season. In addition, indoxacarb was as effective as spinosad and chlorfenapyr and significantly more effective than tebufenozide and emamectin benzoate.     

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.     

Developmental times and life tables for shore flies, Scatella tenuicosta (Diptera: Ephydridae), at three temperatures

Development times and survivorship of immature shore flies and longevity and reproduction of adult shore flies, Scatella tenuicosta Collin, reared on algae-infested filter paper, were studied at three temperatures (constant 20, 26, and 28.5 degrees C) through life table analysis. The development time for each individual life stage and the total time from egg to adult decreased with increasing temperature. Duration of the third (ultimate) larval instar ranged from 3.3 +/- 0.09 d at 20 degrees C to 1.4 +/- 0.04 d at 28.5 degrees C and was 1.7-1.9 times longer than the approximately equal first and second instars. Development of male and female shore flies from egg to adult needed an average of 14.5 +/- 0.13, 8.2 +/- 0.05, and 7.0 +/- 0.04 d at 20, 26, and 28.5 degrees C, respectively, and needed an estimated 154.4 +/- 1.2 thermal units (degree days). At these respective temperatures, adult females lived 21.8 +/- 2.2, 19.9 +/- 2.4, and 15.0 +/- 1.4 d and produced 379 +/- 62, 710 +/- 119, and 477 +/- 83 eggs during oviposition periods of 14.3 +/- 2.1, 15.0 +/- 2.2, and 10.8 +/- 1.4 d; daily lifetime egg production averaged 16.3 +/- 2.3, 33.5 +/- 3.8, and 29.7 +/- 3.5. Developmental stage-specific mortality was relatively low for all life stages at all temperatures, with maximum percent mortalities of 5.7% occurring in both the egg stage and in the third instar. The highest net reproductive rate (R(o)) was obtained for insects reared at 26 degrees C and was 329.6. The intrinsic rate of natural increase (r(m)) was highest at 28.5 degrees C and was 0.430. Generation time and doubling time of the population were shortest at 28.5 degrees C and were 12.4 and 1.6 d, respectively. Results suggested that 26 degrees C was near optimum for reproduction.     

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 Heliothis zea larvae to Nomuraea rileyi at various temperatures

Laboratory studies were conducted to determine the susceptibility of various larval instars of Heliothis zea to different spore doses of Nomuraea rileyi at constant and variable temperatures. The fungus was most effective at 20° and 25°C, with a mortality of 80% and 71%, respectively. At 15°C the disease progressed very slowly with larval mortality occurring in 12–28 days post-treatment. Conversely, at temperature ranges above 15°C, the mortality of the larvae occurred in 6–12 days. Three different combinations of variable temperatures included 20–30°, 25–30°, and 20–35°C, but mortality did not exceed 46%. Larvae in the third to fifth instars were more susceptible to infection than were those in the first and second instars.     

Survival and development of different life stages of three Ceratitis spp. (Diptera: Tephritidae) reared at five constant temperatures

Fruit flies (Diptera: Tephritidae) are the most damaging pests on fruit crops on Réunion Island, near Madagascar. Survival and development of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), the Natal fruit fly, C. rosa Karsch and the Mascarenes fruit fly, C. catoirii Guérin-Mèneville were compared at five constant temperatures spanning 15 to 35 degrees C. Durations of the immature stages of C. capitata, C. rosa and C. catoirii ranged from 14.5-63.8, 18.8-65.7 and 16.8-65.8 days, respectively, at 30-15 degrees C. The lower developmental threshold and thermal constant were calculated using the temperature summation model. The thermal constant for total development of the immature stages of C. capitata, C. rosa and C. catoirii were 260, 405 and 356 DD, respectively. Species differed mainly during the larval stages and ovarian maturation period, with smaller differences in the egg stage. Ceratitis rosa appeared to be better adapted to low temperatures than the two other species as it showed a lower larval developmental threshold of 3.1 degrees C compared to 10.2 degrees C for C. capitata and 8.9 degrees C for C. catoirii. Overall, C. catoirii had a low survival rate within the range of temperatures studied. The different responses of the three Ceratitis species to various temperatures explain to some extent their distribution on the island. The results obtained will be used for optimizing laboratory rearing procedures and for constructing computer simulation models to predict fruit fly population dynamics.     

Susceptibility of immature stages of Chrysoperla rufilabris (Neurop., Chrysopidae) to pyriproxyfen, a juvenile hormone analog

Effects of pyriproxyfen (Knack), a juvenile analog, at three concentrations (10, 50 and100 mg [AI]/l), on survival and development of all immature stages of Chrysoperla rufilabris (Burmeister), were determined in the laboratory. Pyriproxyfen significantly reduced the survival rates when eggs, first and third instars were treated, but not when the second instars and pupae were treated. When eggs were treated, the two higher concentrations reduced the eggs viability by 33.3–50%, and only 0.0–6.7% developed to adults. The lowest concentration of pyriproxyfen (10 mg [AI]/l) caused high mortality on third instars, not on other stages, indicating the third instar was the most vulnerable stage. Pyriproxyfen had significant effects on development for all immature C. rufilabris that successfully developed to adults with variations among the developmental stages and concentrations. The overall developmental duration from eggs to adults when eggs, first, and third instars were treated were 2.6–4.2, 2.4–4.1 respectively, and 6.0–7.1 d longer than those in water control, respectively. However, the overall developmental durations from eggs to adults were 0.5–1.2 d shorter than in water control when the second instars were treated with pyriproxyfen. The compatibility of pyriproxyfen with natural enemies in integrated pest management programs is discussed.     

Hydroprene prolongs developmental time and increases mortality of Indianmeal moth (Lepidoptera: Pyralidae) eggs

Eggs of the Indianmeal moth, Plodia interpunctella (Hübner), were exposed to the labeled rate of hydroprene (1.9 x 10(-3) mg [AI]/cm2) sprayed on concreted petri dishes. These eggs were exposed for 1, 3, 6, 12, and 18 h and until hatching (continuous exposure) at temperatures of 16, 20, 24, 28, and 32 degrees C and 57% RH until the emergence of first instars. The developmental time and egg mortality were significantly influenced by temperature and exposure periods. At 16 degrees C, hydroprene did not cause differences in developmental time when eggs were exposed for different periods. At temperatures >16 degrees C, both exposure period and temperature influenced developmental time. The maximum developmental time (15.0 +/- 0.2 d) occurred at 16 degrees C, and the minimum developmental time (3.2 +/- 0.3 d) occurred at 32 degrees C. Mortality increased when eggs were exposed to hydroprene for longer periods at all of the five tested temperatures. The greatest mortality (81.6 +/- 2.1%) occurred when eggs were continuously exposed on treated surfaces at 32 degrees C. We used developmental time instead of rate (1/ developmental time) to fit simple linear or polynomial regression models to the development data. Appropriate models for developmental time and mortality were chosen based upon lack-of-fit tests. The regression models can be used in predictive simulation models for the population dynamics of Indianmeal moth to aid in optimizing use of hydroprene for insect management.     

Population growth and development of the psocid Liposcelis rufa (Psocoptera: Liposcelididae) at constant temperatures and relative humidities

We investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, and 40.0 degrees C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis rufa Broadhead (Psocoptera: Liposcelididae). L. rufa did not survive at 43% RH, at all temperatures tested; at 55% RH, at the highest four temperatures; and at 63% RH and 40.0 degrees C. The greatest population growth was recorded at 35.0 degrees C and 75% RH (73-fold growth). At 40.0 degrees C, L. rufa populations declined or barely grew. L. rufa males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 31, 54, and 15%, respectively. Female L. rufa have two to five instars, and the percentages of females with two, three, four, and five instars were 2, 44, 42, and 12%, respectively. The life cycle was shorter for males than females. We developed temperature-dependent developmental equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. The ability of L. rufa to reproduce at a relative humidity of 55% and temperatures of 22.5-30.0 degrees C and at relative humidities of 63-75% and temperatures of 22.5-37.5 degrees C, in addition to being able to survive at 40.0 degrees C, suggests that this species would be expected to have a broader distribution than other Liposcelis species. These data provide a better understanding of L. rufa population dynamics and can be used to help develop effective management strategies for this psocid.     

Influence of temperature on developmental rate,wing length,and larval head capsule size of pestiferous midge Chironomus crassicaudatus (Diptera: Chironomidae)

Larvae of Chironomus crassicaudatus Malloch were reared individually at nine constant temperatures from 12.5 to 32.5 degrees C (2.5 degrees C increments) for 120 d. Duration of immature stages (egg, four instars, and pupa), head capsule width of fourth instars, and wing length were recorded. Some adults emerged at all temperatures, except at 12.5 degrees C where individuals developed to fourth instars during the experiment. Sharpe and DeMichele's four-parameter model with high-temperature inhibition described the temperature-dependent developmental rates. The slowest development was observed at 15 degrees C, with developmental rate peaking between 25 and 27.5 degrees C. Developmental rate increased rapidly with increasing temperature up to 20 degrees C, slowed between 20 and 27.5 degrees C, and decreased at temperatures >27.5 degrees C. No developmental inhibition at high temperatures was observed in eggs. The most apparent high-temperature inhibition of development was recorded in fourth instars, which comprised the largest proportion of developmental time. Males developed faster than females, but females had wider larval head capsules and longer wings than males. Adult size was negatively related with temperature in both sexes, but this relationship was steeper in males than in females. Larval size peaked at 20 degrees C, whereas the head capsule width was reduced at temperatures higher and lower than 20 degrees C.     

Temperature-dependent development of Chilocorus bipustulatus (Coleoptera: Coccinellidae)

The effect of temperature on development and survival of Chilocorus bipustulatus L. (Coleoptera: Coccinellidae), a predator of many scale insects, was studied under laboratory conditions. The duration of development of egg, first, second, third, and fourth larval instars, pupa, and preovioposition period at seven constant temperatures (15, 17.5, 20, 25, 30, 32.5, and 35°C) was measured. Development time decreased significantly with increasing temperature within the range 15-30°C. Survival was higher at medium temperatures (17.5-30(ο)C) in comparison with that at more extreme temperature regimens (15 and >30(ο)C). Egg and first larval instars were the stages where C. bipustulatus suffered the highest mortality levels at all temperatures. The highest survival was recorded when experimental individuals were older than the third larval instar. Thermal requirements of development (developmental thresholds, thermal constant, optimum temperature) of C. bipustulatus were estimated with application of linear and one nonlinear models (Logan I). Upper and lower developmental thresholds ranged between 35.2-37.9 and 11.1-13.0°C, respectively. The optimum temperature for development (where maximum rate of development occurs) was estimated at between 33.6 and 34.7°C. The thermal constant for total development was estimated 474.7 degree-days.     

Hot water immersion for surface disinfestation of Maconellicoccus hirsutus (Homoptera: Pseudococcidae)

Mealybug Maconellicoccus hirsutus (Green) adults, nymphs, crawlers, and eggs were tested for their susceptibility to hot water immersion at 47, 48, and 49 degrees C. Eggs inside ovisacs were found most tolerant with prolonged survival compared with other stages at all temperatures. Ovisacs required an average of 1.38, 1.46, and 1.62 times longer treatment duration than adults, nymphs, and crawlers, respectively, for 99.9% predicted mortality at 47, 48, and 49 degrees C. Lethal time estimations were calculated from inverse predictions of regressions derived from logit-transformed data as well as those created using a kinetic model. LT 99.9 estimations were 47.0, 21.2, and 11.9 min at 47, 48, and 49 degrees C, respectively, by using regressions with logit transformations. The kinetic model predictions were 43.9, 19.6, and 11.1 min at 47, 48, and 49 degrees C, respectively. During the study no emergence from eggs inside ovisacs was found after treatments of 52, 24, and 14 min at 47, 48, and 49 degrees C, respectively. Results from this study provide efficacious temperature-time 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.     

Potential increase in fruit fly (Diptera: Tephritidae) interceptions using ionizing irradiation phytosanitary treatments

Irradiation postharvest phytosanitary treatments are used increasingly and show further promise because of advantages compared with other treatments. Its chief disadvantage is that, unlike all other commercially used treatments, it does not provide acute mortality, although it prevents insects from completing development or reproducing. The objective of this research was to determine to what extent irradiated egg and early instars of tephritids would develop to later instars that could be found by phytosanitary inspectors or consumers. Mexican fruit fly, Anastrepha ludens (Loew), eggs and first instars in grapefruit, Citrus paradisi Macfayden, were irradiated with 70-250 Gy and held at approximately equal to 27 degrees C until third instars completed development. The accepted minimum absorbed phytosanitary dose for this pest is 70 Gy, although higher doses may be applied under commercial conditions. The more developed a fruit fly before it was irradiated, the greater the proportion that survived to the third instar. Also, dose was inversely related to developmental success, e.g., a mean of approximately 65 and 35%, respectively, of late first instars reached the third instar when irradiated with 70 and 250 Gy. Of those, 65.1 and 23.4%, respectively, pupariated, although no adults emerged. Irradiation may result in a greater frequency of live (albeit incapable of resulting in an infestation) larvae being found than would be expected compared with other treatments that provide acute mortality. The regulatory community should be aware of this and the fact that it does not increase the risk of irradiation phytosanitary treatments resulting in an infestation of quarantine pests.     

Relationship between supercooling point and mortality at low temperatures in Indianmeal moth (Lepidoptera: Pyralidae)

Indianmeal moth, Plodia interpunctella (Hübner), is classified as a freeze-intolerant organism and one of the most cold-tolerant stored-product pests. The objective of this study was to determine the relationship between mortality at low temperatures after minimum exposure and the supercooling point (SCP) for laboratory-reared P. interpunctella at different stages of development. This relationship also was analyzed for field-collected, cold-acclimated fifth instars. Mean SCP of laboratory-reared larvae (i.e., feeding stage) was consistently above approximately -16 degrees C. Mean SCP of laboratory-reared pupae and adults (i.e., nonfeeding stages) and field-collected, cold-acclimated fifth instars was consistently below approximately -21 degrees CP seemed to be the boundary between survival and death for larvae. However, it seemed that a 1-min exposure was not sufficient to cause larval mortality at the SCP. Alternatively, for both pupae and adults, the SCP seemed not to play an important role in their survival at low temperatures, with significant mortality observed at temperatures higher than the mean SCP. Adults were the most susceptible to low temperatures with no survival occurring at -20 degrees C, > 3 degrees C above its mean SCP. Results of this investigation demonstrate that P. interpunctella has a different response to low temperatures depending on stage of development and cold acclimation. Classifying P. interpunctella only as a freeze-intolerant organism disregards the occurrence of prefreeze mortality in this species. Therefore, a reclassification of this species (e.g., chill tolerant or chill susceptible) based on the extent of prefreeze mortality and the temperature and time of exposure at which it occurs is suggested.