Effect of oriental armyworm <Emphasis Type="Italic">Mythimna separata</Emphasis> egg age on the parasitism and host suitability for five <Emphasis Type="Italic">Trichogramma</Emphasis> species

The oriental armyworm Mythimna separata (Walker) is a major cereal crop pest, causing severe economic losses worldwide every year. Yet, few studies documented the biological control of M. separata using natural enemies such as egg parasitoids of the genus Trichogramma. To evaluate the possibility of biological control of M. separata eggs at various ages (0-, 1-, 2-, and 3-day old), we compared under laboratory conditions the parasitism, emergence, development, and female progeny (sex ratio) of five Trichogramma species indigenous in China: Trichogramma dendrolimi Matsumura, T. chilonis Ishii, T. ostriniae Pang & Chen, T. leucaniae Pang & Chen, and T. japonicum Ashmend. All five Trichogramma species parasitized M. separata at all egg ages but showed a preference for younger eggs. T. dendrolimi parasitized 55.1, 36.6, 19.3, and 14.3 hosts in 24 h on 0-, 1-, 2-, and 3-day-old eggs, respectively, and it exhibited the highest parasitism and suitability on all egg ages. T. japonicum showed the lowest parasitism rate and the poorest host acceptance. T. ostriniae, T. leucaniae, and T. chilonis presented similar rates of adult emergence and sex ratio for all M. separata egg ages. T. ostriniae developed significantly slower on 2- and 3-day-old M. separata eggs. With the exception of T. leucaniae, all species showed no difference in adult emergence at all egg ages. T. dendrolimi was identified as the best for biological control of M. separata. The present study provides valuable information for future development of Trichogramma species in biological control programs targeting M. separata as pest.     

Efficacy assessment of some<Emphasis Type="Italic"> Trichogramma</Emphasis> species (Hymenoptera: Trichogrammatidae) in controlling the potato tuber moth<Emphasis Type="Italic"> Phthorimaea operculella</Emphasis> Zell. (Lepidoptera: Gelechiidae)

Laboratory studies were conducted to assess several life-history characteristics of three Trichogramma species—T. cacoeciae, T. evanescens, and T. principium—reared on potato tuber moth eggs. The effects of host age, parasitoid age, and different temperatures on the mean number of parasitized eggs and the percentage of emerged progeny were determined. The age of both Trichogramma and host eggs significantly affected the number of eggs parasitized by the wasps, but did not affect the percentage of parasitoids emerging from parasitized eggs. No intraspecific differences for potato tuber moth eggs were found among the tested Trichogramma species. However, T. principium proved to be more effective than T. cacoeciae and T. evanescens in parasitizing host eggs at high temperatures (>33 °C). Trichogramma significantly decreased the number of potato tuber moth F₁ emerged progeny when they were released with moths in small cages either over potatoes or potato seedlings.     

Performance of four <Emphasis Type="Italic">Trichogramma</Emphasis> species (Hymenoptera: Trichogrammatidae) as biocontrol agents of <Emphasis Type="Italic">Heliothis virescens</Emphasis> (Lepidoptera: Noctuidae) under various temperature regimes

Trichogramma spp. are major parasitoids of lepidopteran pest eggs, but there is large variation in efficacy toward a given pest among the numerous described Trichogramma species. It is important to select the Trichogramma species that most effectively parasitize and develop in target pest eggs for biological control. In this context, Trichogramma pretiosum, T. exiguum, T. atopovirilia and T. acacioi were studied in Heliothis virescens eggs under different thermal conditions. The parasitoids were reared at constant temperatures of 20, 25 and 30°C and tested at these respective temperatures, while parasitoids reared at 25°C were also tested at 20 and 30°C, for a total of 20 species–temperature combinations. About 30 H. virescens eggs were offered to the parasitoids for 24 h. Among the four species, parasitism rate by T. atopovirilia was highest at all temperature conditions, whereas T. acacioi had the lowest rates of parasitism at 25°C and 25/30°C. Parasitism ranged from 13.8 to 43.8% among all species–temperature combinations. Viability (emerged parasitoids) ranged from 80.8 to 98.4%, and was deemed satisfactory. The emergence rates of T. exiguum and T. acacioi were affected by temperature. Temperature also affected the sex ratio of T. exiguum at 25/30°C, whereas T. pretiosum and T. acacioi produced females predominantly independent of temperature. Overall, the parasitoid T. atopovirilia was the most efficient in parasitizing H. virescens eggs, though the levels of parasitism obtained might not ensure its successful use in biological control programs. The temperature-related differences in biological traits observed in the four Trichogramma species tested hint at the importance of making careful choices regarding climatic conditions where the parasitoid is going to be used when selecting a species for biological control programs.     

Parasitoid and host egg ages have independent impact on various biological traits in a Trichogramma species

Trichogramma (Hymenoptera: Trichogrammatidae) are species used worldwide for the biological control of Lepidopteran pests, notably through inundative releases on millions of hectares. The optimal use of Trichogramma parasitoids in crop protection requires an accurate knowledge of their biology. More specifically, the importance of age factor in parasitoids during the time they forage in crops for host eggs (after initial release) and how the aging of host eggs could impact parasitoid biological traits may be important for overall efficiency in terms of crop protection. In this context, the importance of parasitoid female and host egg ages on parasitism rate and the development of offspring was studied in laboratory conditions on Trichogramma cacoeciae Marchal (Hymenoptera: Trichogrammatidae) and the eggs of the pest Lobesia botrana Denis and Schiffermüller (Lepidoptera: Tortricidae). Host eggs tested were 1–2- and 3–4-day-old, while the ages of T. cacoeciae adult females varied from 1-day-old to 4-day-old post-emergence. When L.?botrana eggs were 3–4-day-old, they were less parasitized by T. cacoeciae than 1–2-day-old eggs, and this was not linked to the age of T. cacoeciae females. The age of parasitoid females has an effect on parasitism, as 1-day-old females produced fewer parasitized eggs than 2, 3, and 4-day-old females. For the total number of L. botrana eggs killed by T. cacoeciae, the two factors did not show significant effects. When L. botrana eggs were 1–2-day-old, parasitoid emergence increased according to the age of parasitoid females with the highest success observed for 3-day-old females. The lowest emergence rates were obtained with T. cacoeciae females 1-day-old. The development time was also longer with the young 1-day-old parasitoid females. This study demonstrated that both the aging of parasitoids and host eggs play a role in the subsequent development of parasitoid offspring. The importance of these results in the context of biological control programs involving Trichogramma parasitoids is discussed.     

Biological characteristics and life tables of Neoseiulus umbraticus Chant (Acari, Phytoseiidae) at three constant temperatures

The development time, survival and fecundity of the generalist predatory mite, Neoseiulus umbraticus Chant, were determined at 20, 25, and 30?°C and 65?±?10?% RH. N. umbraticus females completed development in 9.7, 8.0 and 5.9 days, respectively, using a diet of all life stages of Tetranychus cinnabarinus Boisduval. Total developmental times of males were relatively shorter at 25 and 30?°C than at 20?°C. In general, preoviposition, oviposition, and postoviposition periods of N. umbraticus shortened as temperature increased. The longest survival rate of N. umbraticus of 80.5 days occurred at 20?°C, followed by 67.0 and 57.6 days at 25 and 30?°C, respectively. Mated females laid an average 0.9, 1.3 and 1.4 eggs per female per day and 33.1, 44.0 and 43.6 eggs over their entire lives at 20, 25 and 30?°C, respectively. The sex ratios of this species were 0.57, 0.57 and 0.54 female (female+male) at 20, 25 and 30?°C, respectively. The intrinsic rate of increase (r_m) became greater with rising temperatures from 0.123 at 20?°C to 0.180 at 30?°C. The net reproduction rate (R_o) was highest at 25?°C (25.0 females/female) and lowest at 20?°C (18.8 females/female), while T_o decreased with increasing temperatures, from 23.8 days at 20?°C to 17.5 days at 30?°C.     

Potential for combined use of parasitoids and generalist predators for biological control of the key invasive tomato pest Tuta absoluta

The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has recently invaded Mediterranean countries and is a major pest in tomato crops. Trichogrammatid oophagous parasitoids have shown promising potential for controlling the pest before the yield decreases in the greenhouse. In protected tomato crops (greenhouse), mirid predators are commonly used for biological control of whiteflies and they also prey on T. absoluta. These predators do not attack Trichogramma adults but they may partially decrease the overall impact of parasitoids on T. absoluta if intraguild predation (IGP) occurs on parasitized eggs. Under laboratory conditions, we tested if the mirid predator Macrolophus pygmaeus shows preference between parasitized and unparasitized T. absoluta eggs. We also tested if the predator reduces the number of parasitized eggs on caged tomato plants (microcosms) and assessed the efficacy of natural enemies used alone or together in limiting T. absoluta populations. We found that IGP is inflicted on the parasitoid Trichogramma achaeae by M. pygmaeus and that the risk of IGP depends on the developmental stage of T. achaeae inside the egg because the larva is at risk mostly early in its development (when parasitized egg is still yellow). In addition, we observed that non-consumptive events, likely probing of the predator on parasitized eggs, may induce mortality in parasitoid offspring without actual feeding on parasitized eggs. However, both IGP and non-consumptive events decreased when the predator was not confined with parasitized eggs in small arenas. Despite negative effects of the predator to the parasitoid, results demonstrate that adding Trichogramma parasitoids may significantly increase the level of control of the pest over what could be attained when only the mirid predator M. pygmaeus is present on tomato. Implications of results are discussed regarding potential of these natural enemies for biological control of T. absoluta in greenhouse tomato crops.     

Temperature-dependent differences in biological traits between two strains of <Emphasis Type="Italic">Trichogramma cacoeciae</Emphasis> (Hymenoptera: Trichogrammatidae)

Parasitoids’ efficiency in controlling pests depends not only on their ability to parasitize their hosts but also on how much they are adapted to climatic conditions (notably temperature) of the area where they are planned to be released. In addition, the optimal conditions for production of parasitoids used for inundative releases like Trichogramma spp. may also vary largely as a function of strains. Using the parasitoid Trichogramma cacoeciae Marchal as biological model, we studied how temperature affects important parasitoid efficiency-related biological traits under laboratory conditions. Emergence, mortality rates and fecundity of two strains of T. cacoeciae, one originating from France (Alsace) and the other one from Tunisia (Degache), were compared at constant temperatures of 15, 20, 25 and 30°C. The parasitoids of the French strain showed highest fecundity at 25°C with wasps that had been reared at 20 or 25°C. The Tunisian strain showed the highest fecundity at 25°C, but only when wasps were previously reared at 25 or 30°C. For both strains, the highest mortality occurred among wasps that had laid eggs at 30°C. Emergence rates were relatively high at all temperatures, although the French strain did better at 15–25°C and the Tunisian one at 20–30°C. Because of the differences in biological traits of these two T. cacoeciae strains in relation to the temperature, a judicious choice must be made among the various strains when using this species in biological control programs.     

Zur Biologie der RaubmilbeCunaxa capreolus Berl. (Acari,Prostigmata, Cunaxidae)

Studies on the biology of the predaceous mite Cunaxa capreolus Berl. (Acari, Prostigmata, Cunaxidae) During life cycleCunaxa capreolus Berlese passes through egg, larva, three nymphal stages and adult. Each moving stage is proceeded by a quiescent one. Biological process such as hatching, moulting and mating were investigated. Female usually deposites its eggs singly in protected places. Number of deposited eggs per female, when fed on book lice (Psocoptera), was positively correlated with temperature. It averaged 24.6, 30.7, 40.7, and 43.5 eggs at 15°, 20°, 25° and 30 °C. Incubation period as well as duration of immature stages and adult longevity were negatively effected with temperature. The generation period (from egg to egg) ranged from 24.8 to 64.2 days when temperature changed from 30° to 15 °C. Within these limits of temperature, the simple regression indicated that an increase of 1 °C decreased the generation period for about 2.6 days.     

Influences of host age,sex ratio,population density,and photoperiod on parasitism by <Emphasis Type="Italic">Trichogramma evanescens</Emphasis> Westw. (Hym., Trichogrammatidae)

Moth species Ephestia kuehniella and Sitotroga cerealella are serious pests in cereal-based food processing facilities and stores in Turkey. Control of these pests is undertaken by regular space treatment of infested areas with pesticides. An alternative control method could be the release of parasitic wasps of the genus Trichogramma. In laboratory tests, we use T. evanescens as a parasitic wasp reared on the eggs of Ephestia kuehniella. Adult wasps emerging from the host were maintained in glass tubes at 27±1° C, 60–70±5% r.h and L14:D10 and fed on honey solution. Adults of T. evanescens in vials without food enclosed from host eggs and all died within 1.8days; in comparison, in vials with honey, live adults were evident for 15.2days. Fresh (6–48h) and old (72–96h) host eggs were offered to T. evanescens and fresh eggs were more accepted than old. Host acceptance of females with males in vials was better than without males. The number of females in the vials also influenced the parasitization rate and single female parasitized more eggs. Adults living in light regime (L14:D10 and L6:D18) parasitized more eggs than in total darkness. Results are discussed with relation to enhancing parasitoid effectiveness in biological control in processing facilities and mills.     

Wirkungen von Temperatur und Luftfeuchtigkeit auf die Embryonalentwicklung und das Eischlüpfen bei der SchildzeckeHyalomma marginatum Koch (Acari,Ixodidae)

Effect of temperature and relative humidity on embryonic development and egg hatch ofHyalomma marginatum Koch (Acari, Ixodidae) Effect of different temperatures (25, 30, 35, 40°C) and relative humidity (RH) levels (50, 75, 90%) on embryonic development and hatching ofHyalomma marginatum was investigated. The percentage of dead eggs and embryos, percentage of morphologically normal larvae, percentage of abnormally hatched larvae and percentage of larvae with morphological malformations were determined for each condition. Embryonic development and egg hatch proceeded at 25–35°C in all relative humidity levels tested. However 50% RH was unfavourable for these processes. The optimal conditions for larval development were found to be: temperature of 25–30°C and relative humidity of 75%. Under these conditions 72.7–87.8% of examined egg hatched into normal larvae.     

Über die Mortalität des Erbsensamenkäfers,Callosobruchus maculatus (Fab.) bei hohen Kohlendioxid-Werten

The mortality of adults, eggs, larvae and pupae of the cowpea storage bruchid,Callosobruchus maculatus (Fab.) was observed in four different high carbon dioxide (CO₂) in air atmospheres (88% CO₂, 70% CO₂, 60% CO₂ and 50% CO₂) at 25°C and 32°C respectively, and 70% RH. All the developmental stages ofC. maculatus were completely killed within 5 days in the 88% CO₂ in air atmosphere and within 12 days in the other high CO₂ atmospheres tested. The adult and egg stages were most susceptible, and the old larvae and pupae, the least susceptible to the high CO₂ atmospheres. Mortality ofC. maculatus was significantly influenced by the level of CO₂, stage of insect development, exposure period and temperature.     

Reduction in egg hatch ofArgas (Argas) reflexus (Fab.) (Acari,Argasidae) due to colchicine

The eggs ofArgas (Argas) reflexus (Fab.) were exposed to 0.05% colchicine on 9th, 15th or 23rd–25th days of embryonic development at 25°C and 30% RH. The eggs on the 15th and 23rd–25th days of development were the most sensitive to colchicine. In these experiments 6.9% and 9.4% embryos died, respectively. The largest number of disturbances of egg hatch (11.5%) were observed after exposure of the eggs to colchicine on 23rd–25th days of embryogenesis.     

Pentatomid host suitability and the discovery of introduced populations of <Emphasis Type="Italic">Trissolcus japonicus</Emphasis> in Oregon

Trissolcus japonicus is an egg parasitoid of Halyomorpha halys, brown marmorated stink bug, a severe agricultural pest in the USA. T. japonicus is being evaluated in quarantine as a classical biological control agent to manage H. halys populations in the USA. To determine T. japonicus’ potential for successful management of the pest, we performed a series of no-choice and paired-host-range tests, evaluating parasitism and host recognition in ten nontarget insects. In laboratory no-choice tests, T. japonicus successfully parasitized egg masses of seven Pentatomidae native to Oregon in addition to H. halys. Mean parasitism proportions of egg masses were greater than 40% in two species, B. dimidiata and H. abbreviatus, and were statistically similar to parasitism of H. halys. However, paired-host tests identified higher proportions of parasitized H. halys egg masses compared to four other pentatomids. T. japonicus was equally attracted to volatiles produced by H. halys and other pentatomids but demonstrated significantly longer arrestment response time on surfaces with H. halys contact kairomones. Although host acceptance patterns were similar between stink bug species, our results suggest a greater potential for parasitoid development in H. halys eggs compared to the native pentatomids. During host-range testing, we detected field populations of T. japonicus at 11 sites in Portland, OR, indicating an unintentional introduction and establishment. Further work is needed to characterize its nontarget activity and dispersal patterns in areas where H. halys causes economic damage in Oregon.     

The optimum temperature–humidity combination for the feeding activities of Japanese subterranean termites

Two species of Japanese subterranean termite, Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe), were used in an investigation of the optimum temperature–relative humidity (RH) combination for their feeding activities. Daily wood consumption per worker and survivals were measured, and the protozoan fauna in the hindgut were observed under 15 temperature–RH combinations for 1 week. Five temperatures (20°, 25°, 30°, 35°, and 40°C) and three RH conditions (50%, 70%, and 90% RH) were examined. The activities of the workers were highest at around 30°C for both species, and workers died at 40°C within 5 days and 2 days for C. formosanus and R. speratus, respectively. The optimum RH condition for feeding activity was 90% RH for C. formosanus and 70%–90% RH for R. speratus. The optimum temperature–RH combinations for feeding activities were 30°C at 90% RH for C. formosanus and 30°C at 70%–90% RH for R. speratus.     

Factors influencing the parasitism of codling moth eggs by Trichogramma cacoeciae March. and T. principium Sug. et Sor. (Hymen. Trichogrammatidae)

Non-choice laboratory experiments were conducted to evaluate the influence of host acceptance, previous rearing host, host age and the contact time between parasitoids and host on the efficacy of Trichogramma cacoeciae Marchal and T. principum Sug. et Sor. against the codling moth Cydia pomonella. The tendency of T. cacoeciae and T. principum females to attack the codling moth was similar to E. kuehniella, and it was not affected by the previous rearing host. T. cacoeciae showed a greater preference for codling moth eggs than T. principum. A high mean number of emerged F₁ progeny was observed when both parasitoids were sequentially reared on codling moths. Codling moth acceptance, the number of parasitized eggs and the number of emerged progeny were higher when younger codling moth eggs were offered. The tendency of female parasitoids to oviposit remained unchanged when the contact time with the host was prolonged. When the contact time was increased, the number of parasitized eggs and emerged offspring was higher. The results showed that the codling moth fertility (egg hatch) was reduced when younger eggs were offered and when the contact time with the parasitoids was increased. T. cacoeciae was more efficient in reducing codling moth fertility. The current study provided essential information necessary to increase the efficiency of T. cacoeciae and T. principum against the codling moth.     

Evaluation of the temperature and relative humidity preferences of the western dry-wood termite <Emphasis Type="Italic">Incisitermes minor</Emphasis> (Hagen) using acoustic emission (AE) monitoring

Twenty-four different combinations of six temperatures (15°, 20°, 25°, 30°, 35°, and 40°C) and four relative humidity (RH) (60%, 70%, 80%, and 90%) conditions were used for pseudergates of the western dry-wood termite Incisitermes minor (Hagen). The feeding activities of the termites were monitored by the detection of generated acoustic emission (AE) events from feeder wood blocks in a test chamber. Temperature and RH showed independent and interactive significant effects on the feeding activity of I. minor. The optimal temperature and RH conditions for the feeding activities were 35°C and 70%, respectively, and the optimal combinations were 35°C-70% and 35°C-80% with an exceptionally higher feeding activity at the combination condition of 30°C-70%.     

Laboratory studies on the effect of temperature and humidity on the life table of the whitefly,Aleurotuberculatus takahashi David & Subramaniam (Hom., Aleyrodidae) from southeastern China

The present paper deals with developmental duration, emergence, longevity and fecundity ofAleurotuberculatus takabashi David & Subramaniam at different temperatures and humidity levels. The developmental time from egg to adult was 81.8, 56.9, 39.6, 29.9, 20.6 days at 15±1, 20±1, 25±1, 30±1, 35±1°C under constant relative humidity (RH) of 70±5%, respectively. At 25±1°C, the total developmental time was slightly affected by humidity, ranging from 46.4 days at 40±5% RH to 39.2 days at 90±5% RH. The developmental threshold and the thermal constant for the stage from egg to adult were 10.1°C and 542.8 day-degrees. It was estimated that the whitefly has about 10 generations a year in Fuzhou region in southeastern China. Lowest mortality rates of 12.4% for the egg, 6.8% for the nymph and 3.1% for the puparium were obtained at 15±1°C, while they were highest with 92.1% for the egg, 48.2% for the nymph and 36.3% for the puparium at 35±1°C. The mortality rates were slightly affected by humidity, ranging from 17.6% at 40±5% RH to 27.9% at 90±5% RH for the egg, 11.2% at 40±5% RH to 19.6% at 90±5% RH for the nymph, and 6.4% at 40±5% RH to 11.6% at 90±5% RH for the puparium. The emergence rate of adults decreased as temperature increased, ranging from 89.1% at 15±1°C to 21.5% at 35±1°C, so did the longevity of adults, ranging from 9.6 days at 15±1°C to 2.9 days at 35±1°C. The number of eggs per female was significantly affected by temperature (P.01), valuing 29.4 eggs per female at 15±1°C, 36.7 at 20±1°C, 52.4 at 25±1°C, 42.9 at 30±1°C, and 6.1 at 35±1°C. The optimal temperature for reproduction was about 25°C.     

Functional responses of the parasitoid,Ertmocerus longipes Compere (Hym., Aphelinidae) to densities of the whitefly,Aleurotuberculatus takahashi David et Subramaniam (Hom., Aleyrodidae) at different temperatures

The present study dealt with the functional responses of the parasitoid,Eretmocerus longipes Compere (Hym., Aphelinidae) to the densities of the whitefly,Aleurotuberculatus takahashi David et Subramaniam (Hom., Aleurodidae) at different temperatures under the laboratory conditions. The results showed that when the initial densities ofA. takahashi-3rd instar were raised from 10 to 320 ind./leaf, the numbers of parasitized nymphs increased as well, ranging from 7.0 to 23.1 at 20°C, 9.8 to 42.9 at 25°C, 6.7 to 39.9 at 30°C, and 1.8 to 8.3 ind./leaf at 35°C, respectively. The Holling Disk Equation was introduced to build up the models of functional responses. The response curves remained type II, although the numbers of parasitized nymphs were significantly different under different temperatures. The suitable initial densities of the host whitefly for parasitization were about 80 individuals per leaf. A negative relation was observed between the initial densities of the whitefly and the parasitization rates by the parasitoid. An increase in the initial densities ofA. takahashi-3rd instars ranging from 10 to 320 ind./leaf resulted in a decrease in the parasitization rate byE. longipes ranging from 70.0% to 7.2% at 20°C, 98.0% to 13.4% at 25°C, 67.0% to 12.5% at 30°C and 18.0% to 2.6% at 35°C with a value of 0.2877 was significantly smaller than that at 20°C with a vlaue of 1.3354, that at 25°C with a value of 1.6465 and that at 30°C with a value of 1.1199, respectively (p<0.01). The handling time (Th) forE. longipes was 0.1521 at 35°C, significantly longer than 0.0510 at 20°C, 0.0289 at 25°C and 0.0320 at 30°C, respectively (p<0.01). The maximum loading number (K) of the parasitized nymphs with a value of 34.5 ind./leaf at 25°C was similar to that with a value of 31.2 ind./leaf at 30°C, about 1.8 times as high as that with a value of 19.6 ind./leaf at 20°C and 4 times more than that with a value of 6.6 ind./leaf at 35°C. It was suggested that temperature affected the functional response by balancing searching rate and handling time. The optimal temperature range for the functional responses ofE. longipes to the densities ofA. takahashi-3rd instar was 25° to 30°C.     

Prey consumption during development as well as longevity and reproduction of <Emphasis Type="Italic">Typhlodromus pyri</Emphasis> Scheuten (Acari,Phytoseiidae) at higher temperatures in the laboratory

The predatory mite Typhlodromus pyri Scheuten (Acari, Phytoseiidae) has been reported as an important predator of the European red mite, Panonychus ulmi (Koch) (Acari, Tetranychidae) in apple culture and vineyards at below 25?°C. However, sufficient biological data was lacking on its efficiency at temperatures above 25?°C. Therefore, the purpose of the present laboratory work was to obtain experimental data on prey consumption during development as well as longevity and reproduction of T. pyri on apple leaf discs and in Plexiglas cells at constant temperatures of 25?±?2?°C and 30?±?2?°C with P. ulmi as prey.     

Evaluation of the concentrations of hydrogen and methane emitted by termite using a semiconductor gas sensor

A gas detection apparatus equipped with a semiconductor gas sensor was employed for qualitative and quantitative measurement of hydrogen and methane emitted by termites. A gas sample of 2.5 ml was injected into the semiconductor gas sensor through the gas detection apparatus, and the maximum voltage of the sensor was converted into gas concentration. The gas samples were collected from three distinct experiments: (1) five combinations of workers and soldiers of Coptotermes formosanus with and without a wood specimen; (2) C. formosanus under six temperature conditions; and (3) four different termite species, C. formosanus, Reticulitermes speratus, Incisitermes minor, and Zootermopsis nevadensis. The hydrogen and methane concentrations increased with an increase in the number of termites. Concentrations were higher in samples with a wood specimen than without it. Both hydrogen and methane concentrations were the highest for the samples at 35 °C and were lowest at 15 and 5 °C. The concentrations were very low at 45 °C because all the termites had died in a few hours. The concentrations of hydrogen and methane were highest for Z. nevadensis, the dampwood termite, among the four species, and no methane was detected for I. minor, the drywood termite, at 28 °C and 75 % RH.