Biological characteristics and thermal requirements of a Brazilian strain of the parasitoid Trichogramma pretiosum reared on eggs of Pseudoplusia includens and Anticarsia gemmatalis

A new strain of the parasitoid Trichogramma pretiosum, was collected in Rio Verde County, State of Goiás, Central Brazil, and designated as T. pretiosum RV. This strain was then found to be the most effective one among several different strains of T. pretiosum tested in a parasitoid selection assay. Therefore, its biological characteristics and thermal requirements were studied, aiming at allowing its multiplication under controlled environmental conditions in the laboratory. The parasitoid was reared on eggs of Pseudoplusia includens and Anticarsia gemmatalis at different constant temperatures within an 18–32 °C temperature range. The number of annual generations of the parasitoid was also estimated at those temperatures. Results have shown that T. pretiosum RV developmental time, from egg to adult, was influenced by all temperatures tested within the range, varying from 6.8 to 20.3 days and 6.0 to 17.0 days on eggs of P. includens and A. gemmatalis, respectively. The emergence of T. pretiosum RV from eggs of A. gemmatalis was higher than 94% at all temperatures tested. When this variable was evaluated on eggs of P. includens, however, the figures were higher than that within the 18–30 °C range (more than 98%), and were also statistically higher than the emergence observed at 32 °C (90.2%). The sex ratio of the parasitoids emerged from eggs of A. gemmatalis decreased from 0.55 to 0.29 at 18–32 °C, respectively. However, for those emerged from eggs of P. includens, the sex ratio was similar (0.73, 0.72 and 0.71) at 20, 28 and 32 °C, respectively. The lower temperature threshold (Tb) and thermal constant (K) were 10.65 °C and 151.25 degree-days when the parasitoid was reared on eggs of P. includens; and 11.64 °C and 127.60 degree-days when reared on eggs of A. gemmatalis. The number of generations per month increased from 1.45 to 4.23 and from 1.49 to 4.79 when the parasitoid was reared on eggs of P. includens and A. gemmatalis, respectively, following the increases in the temperature.     

Trichogramma pretiosum parasitism of Pseudoplusia includens and Anticarsia gemmatalis eggs at different temperatures

Egg parasitism of Trichogramma pretiosum strain RV when presented with eggs of Anticarsia gemmatalis and Pseudoplusia includens was investigated at 18, 20, 22, 25, 28, 30 and 32 °C. The number of eggs parasitized per day decreased for both hosts as a function of the age of parasitoids, reaching 80% of lifetime parasitism more rapidly as temperature increased; on the 4th day at 32 °C and on the 12th day at 18 °C. The lifetime number of parasitized P. includens eggs achieved by the parasitoid maintained at 20 °C (44.95 ± 3.94) differed from the results recorded at 32 °C (28.5 ± 1.33). Differently, the lifetime number of A. gemmatalis parasitized eggs did not differ among the temperatures. When T. pretiosum reached 100% of lifetime parasitism, each adult female had parasitized from 28.5 ± 1.33 to 44.95 ± 3.94 and from 29.58 ± 2.80 to 45.36 ± 4.50 P. includens and A. gemmatalis eggs, respectively. Also, the longevity of these adult T. pretiosum females, for which P. includens or A. gemmatalis eggs were offered, was inversely correlated with temperature. Not only were the survival curves of those adult T. pretiosum females of type I when they were presented with eggs of A. gemmatalis but also with eggs of P. includens, i.e., there was an increase in the mortality rate with time as the temperature increased. In conclusion, T. pretiosum strain RV parasitism was impacted by temperature when on both host eggs; however, the parasitoid still exhibited high survival and, more importantly, high number of parasitized A. gemmatalis and P. includens eggs even at the extremes tested temperatures of 18 and 32 °C. Those results indicate that T. pretiosum strain RV might be well adapted to this studied temperature range and, thus, be potentially suitable for use in biological control programs of P. includens and A. gemmatalis in different geographical areas that fits in this range. It is important to emphasize the results here presented are from laboratory studies and, therefore, field trials still need to be carried out in the future with this strain in order to support the full development of the technology intend to use this egg parasitoid in soybean fields worldwide.     

Reproductive and developmental biology of Gonatocerus ashmeadi (Hymenoptera: Mymaridae), an egg parasitoid of Homalodisca coagulata (Hemiptera: Cicadellidae)

The reproductive and developmental biology of Gonatocerus ashmeadi Girault, a parasitoid of the glassy-winged sharpshooter Homalodisca coagulata (Say), was determined at five constant temperatures in the laboratory: 15; 20; 25; 30; 33 °C. At 30 °C, G. ashmeadi maintained the highest successful parasitism rates with 46.1% of parasitoid larvae surviving to adulthood. Lifetime fecundity was greatest at 25 °C and fell sharply as temperature either increased or decreased around 25 °C. Temperature had no effect on sex ratio of parasitoid offspring. Mean adult longevity was inversely related to temperature with a maximum of 20 days at 15 °C to a minimum of eight days at 33 °C. Developmental rates increased nonlinearly with increasing temperatures. Developmental rate data were fitted with the modified Logan model for oviposition to adult development times across each of the five experimental temperatures to determine optimal and upper lethal temperature thresholds. The lower developmental threshold estimated by the Logan model and linear regression were 1.10 and 7.16 °C, respectively. Linear regression of developmental rate for temperatures 15–30 °C indicated that 222 degree-days were required above a minimum threshold of 7.16 °C to complete development. A temperature of 37.6 °C was determined to be the upper development threshold with optimal development occurring at 30.5 °C. Demographic parameters were calculated and pseudo-replicates for intrinsic rate of increase (r_m), net reproductive rates (R_o), generation time (T_c), population doubling time (T_d), and finite rate of increase (λ) were generated using the bootstrap method. Mean bootstrap estimates of demographic parameters were compared across temperatures using ANOVA and nonlinear regression.     

Effects of temperature on development, survival, longevity, and fecundity of the Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) predator, Axinoscymnus cardilobus (Coleoptera: Coccinellidae)

Axinoscymnus cardilobus (Homoptera: Aleyrodidae) is an important predator of Bemisia tabaci (Coleoptera: Coccinellidae) that occurs in high population density of B. tabaci. Temperature among other factors is observed to play an important role in the development of arthropods. The effect of temperature on the development of A. cardilobus was studied at seven constant temperature regimes (14, 17, 20, 23, 26, 29, 32 °C). The results indicated that the duration of egg, larval and pupal stages were significantly influenced by increased temperature. The rate of development gradually increased with increase in temperature from 14 °C to 26 °C, but declined from 26 °C to 32 °C. The survival rates of different insect stages were stable at temperatures between 20 °C and 26 °C, but at extreme temperatures of 32 °C and 14 °C, a sharp decrease was evident. Ovipositional period of the female decreased when temperatures were increased from 17 °C to 32 °C. The highest fecundity of the female (225.7 eggs per female) was recorded at 23 °C. Life tables of A. cardilobus were constructed based on the experimental results at temperatures of 14–32 °C. The reproductive rate (R₀), the innate capacity for increase (r_m) and the finite rate of increase (λ) reached the maximum values at 23 °C, of 70.7, 0.059 and 1.062, respectively. The mean generation time (T) decreased with increased temperature from 17 °C to 32 °C, the highest and least values recorded at 17 °C and 32 °C were 112.7 and 38.7, respectively. These results offer valuable insight on the importation and establishment of A. cardilobus into new environments with diverse temperature regimes.     

The effects of water temperature and ration size on growth and body composition of fry of common carp, Cyprinus carpio

Experiment was conducted with the aim of determining the effect of varying water temperature and ration size on growth and body composition of fry of the common carp, Cyprinus carpio. Common carp fry with an initial body weight (BW) of 0.86 g were fed a diet (34.9% protein, 18.3 KJ/g diet) at four ration sizes 4%, 5%, 6% and 7% of their body weight per day and reared at two water temperatures 28 and 32 °C for 60 days. Fry fed with 6% ration showed the highest mean final body weight at 28 °C. Final body weight was significantly (P<0.05) affected by ration and temperature. Cyprinus carpio fry raised at 28 °C had higher feed efficiency (FE) (44.36%) than the fry reared at 32 °C (40.98%) with 4% ration. Further, feed efficiency decreased with increase in ration levels in both temperatures. Protein efficiency ratio (PER) was higher (1.26) at 28 °C than at 32 °C (1.17). At 6% ration, common carp fry showed highest specific growth rate (SGR) (3.82%/day) at 28 °C as compared with at 32 °C (3.57%/day). A linear increase in protein and lipid contents was evident with increasing ration levels up to 6% body weight at both temperatures 28 and 32 °C. Second-order polynomial regression analysis of weight gain and SGR indicated the breakpoints at ration level 6.04% and 6.08% body weight per day at 28 and 32 °C. Hepatosomatic index (HSI) not affected by temperature and ration size while, viscerosomatic index (VSI) influenced (P<0.05) by ration size and temperature. Based on the above results, it may be concluded that 6% BW/day ration is optimal for growth of Cyprinus carpio fry at both the temperatures 28 and 32 °C.     

Oviposition and reproductive performance of a generalist parasitoid (Trichogramma pretiosum) exposed to host species that differ in their physical characteristics

The response of generalist egg parasitoids to alternative natural hosts that are present simultaneously is not well known. We investigated the behavior of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in relation to two field hosts Helicoverpa armigera Hübner and Spodoptera litura Fabricius, in choice and no choice tests. We quantified the effects of natal host species and post-emergence adult age on the oviposition preference of the parasitoids. H. armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs (average of 17 ± 2.7 vs. 13 ± 3.0, H. armigera to S. litura). The adult lifespan and lifetime fecundity of T. pretiosum were variable but were affected by natal host species and/or host species to which they were exposed. Mean lifespan and fecundity of parasitoids that had developed in H. armigera eggs and were exposed to H. armigera eggs for oviposition were 13.9 ± 1.8 days and 98.7 ± 11.0 adult offspring. By contrast, those that developed in S. litura eggs and were exposed to S. litura eggs for oviposition lived for 7 ± 0.9 days and produced 53.8 ± 8.0 adult offspring. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better than S. litura eggs. These results are used to predict parasitoid behavior in the field when both hosts are available.     

Effect of cold storage on survival, reproduction and development of adults and eggs of Franklinothrips vespiformis (Crawford)

Cold storage effects on both female adults and eggs of the predatory thrips Franklinothrips vespiformis (Crawford) (Thysanoptera: Aeolothripidae) were investigated. The effect of low temperatures (5.5, 7.0, 8.5, 10.0 and 12.5 °C) on survival of F. vespiformis adults was firstly recorded. Survival times were significantly reduced at the lower temperatures tested, whereas storage at 10.0 and 12.5 °C provided the longest survival. Life-history consequences of exposing adults to moderately low temperatures were examined in terms of pre-oviposition period, oviposition rate, egg viability and survival after storage. Adults stored at 7.0 °C showed longer pre-oviposition period and shorter longevity than unstored females but other reproductive attributes were not significantly affected by storage regime. Low temperature and storage period affected egg viability and subsequent development of pre-imaginal stages. No eggs hatched after a 20-day period of storage at 5.5 and 7.0 °C, whereas eggs stored at 12.5 °C hatched significantly faster than ones stored at 10.0 °C and unstored eggs. Increasing the egg storage period from 10 to 20 and 30 days decreased the oviposition rate of adults and egg viability. An essential component in the successful mass rearing and distribution of these predators is the development of a reliable storage schedule of eggs and adults. Long-term storage was unsatisfactory, however their short-term storage (3.5 weeks at 10.0 and 12.5 °C for adults and 4–5 weeks at 12.5 °C for eggs) gave satisfactory results, which suggest the efficacy of such storage during the mass production of the biocontrol agent.     

Host Preferences of Trichogramma pretiosum and the Influence of Prior Ovipositional Experience on the Parasitism of Plutella xylostella and Pseudoplusia includens Eggs

Trichogramma wasps are generalist egg parasitoids used in biological control efforts. In a multi host situation they may preferentially parasitize a non-target host species to the detriment of the control program. Plutella xylostella Linnaeus (Lepidoptera: Plutellidae) is a very serious pest of cabbage, but is only one in a number of species in the ‘cabbageworm’ complex. We investigated the host preferences of Trichogramma pretiosum Riley (Hymenoptera: Chalcidoidea) when offered the eggs of Plutella xylostella and the eggs of Pseudoplusia includens Hübner (Lepidoptera: Noctuidae), another species in the ‘cabbageworm’ complex. Trichogramma pretiosum reared on the eggs of the factitious host Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) parasitized both Plutella xylostella and Pseudoplusia includens eggs under laboratory conditions. For both choice and no-choice experiments, T. pretiosum parasitized significantly more P. xylostella eggs than P. includens eggs. Prior ovipositional experience with one or other of the two host species had no effect on the subsequent parasitism levels of the two host species. The preference for P. xylostella eggs was also not affected by this prior ovipositional experience.     

Production of Anagrus epos Girault (Hymenoptera: Mymaridae) on Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) eggs

Anagrus epos Girault (Hymenoptera: Mymaridae) is a natural enemy candidate for a classical biological control program targeting the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), in California. Little is known about the biology or ecology of A. epos when it utilizes GWSS eggs as a host. Here, we report the results of laboratory studies that describe the host age preference for oviposition, longevity of A. epos adults provided with different food sources, and developmental rates at six different constant temperature regimes. Anagrus epos is a gregarious parasitoid in GWSS eggs with up to 14 adults emerging from each GWSS egg. In choice and no-choice tests for oviposition, A. epos females successfully parasitized all developmental ages of GWSS eggs (1–8 days old). In choice tests, parasitism rates were significantly higher in 1-, 3-, 4-, and 5-day-old GWSS eggs than in 2-, 6-, 7-, and 8-day-old eggs. If provided with honey and water, honey only, water only, or no food or water, A. epos females lived on average 8.2, 4.7, 2.6, and 1.6 days, respectively. Anagrus epos required 294.1 degree-days above a lower temperature threshold of 12.4 °C to develop from egg to adult (eclosion). Our results provide baseline information useful in the development of an efficient parasitoid mass rearing program for A. epos release and evaluation in California.     

Reproductive biology of Fopius ceratitivorus (Hymenoptera: Braconidae), an egg–larval parasitoid of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae)

The reproductive biology of Fopius ceratitivorus Wharton, a recently discovered African parasitoid, was studied in quarantine in Hawaii to facilitate its mass production for biological control of the Mediterranean fruit fly, Ceratitis capitata. Mean longevity of host-deprived and ovipositing females was 17.3 ± 0.9 d and 16.2 ± 0.5 d, respectively. Ovarian maturation peaked at 61.6 mature eggs per female on the fifth day after eclosion and declined thereafter. Mean number of offspring produced per day by mated females was 5.1 ± 0.4, and realized fecundity expressed as total eggs deposited during the female’s life time was 107.8 ± 12.8. Females were more attracted, to and reproduced significantly more, in fruit substrates containing odors of adult flies and eggs rather than fruit substrates artificially inoculated with fly eggs. Our findings suggest that F. ceratitivorus is a promising new parasitoid for biological control of C. capitata in Hawaii.     

Acceptance and suitability of different host stages of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) and seven other tephritid fruit fly species to Tetrastichus giffardii Silvestri (Hymenoptera: Eulophidae)

Tetrastichus giffardii Silvestri is a gregarious eulophid endoparasitoid of several tephritid fruit fly species. Host stage suitability was studied using nine age groups of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), namely, eggs less than 24 h and between 24 and 48 h old, and 1- to 7-day-old larvae. Life table studies for T. giffardii using C. capitata as host were done at 26 ± 5 °C and 55–60% RH. Egg load in relation to age of the female parasitoid was also assessed as was the effect of host deprivation on adult longevity. Host acceptance and suitability were examined with respect to eight species of tephritids. Potential hosts so tested were five Ceratitis species, the Medfly, C. capitata, the mango fruit fly, Ceratitis cosyra (Walker), the Natal fruit fly, Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi), and Ceratitis anonae Graham; two Bactrocera species, the melon fruit fly, Bactrocera cucurbitae (Coquillett) and the newly invasive Bactrocera invadens Drew, Tsuruta, and White; and one Dacus species, the lesser pumpkin fly, Dacus ciliatus Loew. No parasitoids were obtained from eggs while all larval stages were suitable though at varying degrees. Parasitism and number of progeny was related to host age in a curvilinear manner with maxima at 4- to 5-day-old larvae. By contrast, development time decreased with age of host larvae while sex ratio was not affected. The intrinsic rate of increase was 0.17 ± 0.01; gross and net reproductive rates were 64.9 ± 4.3 and 44.9 ± 3.8, respectively. Non-ovipositing females lived significantly longer than ovipositing ones. The females accepted all host species tested, but only C. capitata, D. ciliatus and, to a much lesser extent, C. cosyra were suitable. In the remaining host species, most eggs were encapsulated. In C. capitata and D. ciliatus, percent parasitism was similar, but number of progeny was lower and the sex ratio, as the proportion of females, was higher when the parasitoid was reared on D. ciliatus. Progeny per puparium were also similar for the two hosts. In the light of these results it can be concluded that T. giffardii has a narrow host range, but it attacks and successfully develops in larvae representing a wide range of ages.     

Life history of the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Kenya

We conducted laboratory and field experiments to elucidate the life history of Ixodiphagus hookeri, a parasitoid of the ixodid tick Amblyomma variegatum in Western Kenya. Ixodiphagus hookeri females oviposited in unfed host nymphs as well as engorged nymphs, but rarely in engorged larvae. While I. hookeri developed to adults in engorged nymphs, the eggs laid in unfed nymphs disappeared within 2 days after oviposition. As temperature increased, development time of I. hookeri from oviposition to adult emergence in engorged nymphs decreased from 46 days at 23 °C to 35 days at 28 °C, and their immature survival in engorged nymphs decreased from 67% at 23 °C to 22% at 28 °C. No parasitoid adult emerged from hosts at 30 °C. Individual hosts parasitized by single females produced 42–53 adult wasps, 73% of which were females. As a typical pro-ovigenic species, I. hookeri females had an average of 84 mature eggs at emergence and lived only for a few days. When laboratory-reared, unfed nymphs of A. variegatum were attached to cattle for 4–9 days in subsistence farmers’ fields in Western Kenya, 25% of the engorged nymphs and 4% of the unfed nymphs on cattle were parasitized by I. hookeri, demonstrating that I. hookeri females search for and oviposit in A. variegatum nymphs on cattle. Unlike other strains of I. hookeri that overwinter as eggs in unfed nymphs, I. hookeri could continuously reproduce throughout the year in Western Kenya.     

Effect of Temperature on the Life History of Cirrospilus sp. near lyncus (Hymenoptera: Eulophidae), a Parasitoid of Phyllocnistis citrella (Lepidoptera: Gracillariidae)

The effect of four constant temperatures on the life history of Cirrospilus sp. near lyncus was examined in the laboratory. This species is one of the most abundant generalist indigenous parasitoids of the citrus leafminer, Phyllocnistis citrella Stainton, in Spain. Adult lifespan of C. sp. near lyncus decreased from 50.2 to 9.1 days as temperatures increased from 15 to 30°C, respectively. Both gross fecundity and host-feeding were highest at 20°C (170.48 eggs and 32.33 hosts). Oviposition rates were optimal at higher temperatures (5.22 eggs per day at 25°C and 4.79 eggs per day at 30°C) and were dependent on female age. In contrast, host-feeding rates for a given temperature did not depend on age. Generation time decreased with increasing temperatures from 68.05 days at 15°C to 12.19 days at 30°C. Net reproduction peaked at 20°C (68.86 viable females per female). Intrinsic rate of increase doubled from 15°C (0.059 females per female per day) to 20°C (0.127 females per female per day) and almost doubled again from 20 to 30°C (0.210 females per female per day). Given these parameters, C. sp. near lyncus could perform optimally in the area occupied by P. citrella in the Mediterranean region.     

The Effect of Rearing Temperature on Flight Initiation of Trichogramma sibericum Sorkina at Ambient Temperatures

Trichogramma sibericum Sorkina was reared in the laboratory at three temperatures: 16, 21, and 26°C. Individuals from each of these treatments were then tested for propensity to initiate flight at one of four ambient temperatures: 16, 19, 21, or 26°C. Both rearing and ambient temperatures had significant effects on flight initiation. Insects reared at 16°C had the highest mean proportion of flyers; insects reared at 26°C had the lowest. The proportion of insects initiating flight increased with increasing ambient temperature. Also, the interaction of these two temperature experiences was significant. Insects reared at 16°C were more likely to initiate flight at 16°C than insects reared at 21 or 26°C. These results indicate that performance (as assessed by flight initiation) at ambient temperature is dependent on the temperature previously experienced during rearing.     

Efficacy of an oil-based formulation combining Metarhizium rileyi and nucleopolyhedroviruses against lepidopteran pests of soybean

A biopesticide that combines Metarhizium rileyi and nucleopolyhedrovirus (NPV) in an oil dispersion (OD) was developed. Its efficacy against Anticarsia gemmatalis and Chrysodeixis includens was evaluated under laboratory and field conditions. First, each of the two selected fungal strains, combined or not in OD preparations with AgMNPV or ChinNPV, was tested in the laboratory against A. gemmatalis and C. includens, respectively. AgMNPV–fungus combinations had similar effect on overall mortality of A. gemmatalis compared to each pathogen used alone. C. includens was less susceptible to infection by M. rileyi strains, and ChinNPV became the major cause of larval death. The OD formulations with M. rileyi and/or NPV were applied in infested soybean fields. ChinNPV + M. rileyi caused 50.8% of overall mortality six days after spraying in a soybean crop infested by both pests, whereas for treatments with the fungus or the virus alone the percentages were 41.2% and 8.8%, respectively. In another field infested solely by A. gemmatalis, insect mortality was similar for the AgMNPV–fungus combination and the virus used alone. Larval parasitism by wasps and dipterans was not affected following biopesticide spraying. Our results suggest that the performance of a dual-action biopesticide is related to the NPV and fungal strains that are combined and the proportion of host populations simultaneously infesting the crop.     

Effect of variable dew temperatures on infection of green foxtail by Pyricularia setariae, Drechslera gigantea, and Exserohilum rostratum

A thermogradient apparatus was used to investigate the effect of variable dew temperatures on infection of green foxtail by the indigenous pathogen Pyricularia setariae (Ps) and the exotic pathogens Drechslera gigantea (Dg), and Exserohilum rostratum (Er) from the southern USA that showed bioherbicide potential against several grassy weeds. This device is capable of creating multiple diurnal temperature cycles, mimicking daily temperature fluctuations that occur under field conditions. Seven temperature regimes, i.e., 15/10 °C, 20/5 °C, 20/15 °C, 25/10 °C, 25/20 °C, 30/15 °C, and 30/25 °C (maximum/minimum), were used with temperature cycling from maximum to minimum and then back up to maximum in a 24 h period. Ps and Dg were much more virulent than Er on green foxtail, resulting in higher levels of disease and weed control. Dg was little affected by the dew temperatures in terms of plant infection and was more efficacious than Ps under cooler dew temperatures (15/10 °C and 20/5 °C), causing twice as much disease. This greater amount of disease coincided with higher conidial germination, appressorial formation and infection-hypha frequency by Dg at the lower temperatures. The efficacy of Ps improved as dew temperature increased, accompanied by a higher percentage of germination and more frequent appressorial production. Dg caused severe disease 2 d after inoculation whereas Ps required 4 d to initiate disease symptoms. These observations suggest that Dg is a superior candidate than Ps for green foxtail control on the Canadian prairies.     

Thermal requirements for the embryonic development of Periplaneta americana (L.) (Dictyoptera: Blattidae) with potential application in mass-rearing of egg parasitoids

The embryonic development of oothecae of Periplaneta americana was evaluated under four different constant temperatures (5, 10, 15, 20, 25, 30, and 35 °C) and also at different exposure times at <5 °C. Their suitability as hosts after the treatment for the parasitoids Evania appendigaster and Aprostocetus hagenowii was also assessed. Temperatures of 5, 10, 15, and 35 °C adversely affected the development of the cockroaches, and exposure times to <5 °C longer than 5 days sufficed to kill all the embryos in the oothecae. The lower thermal threshold for complete development of P. americana was estimated to be 6.8 °C, with a required total amount of 900.9 degree-days. Cold-killed oothecae were still fit for the development of parasitoids. Parasitism rates of A. hagenowii were higher than those of E. appendigaster, although with lower emergence rates. Our results can be useful in aiding mass-rearing of these parasitoids for biological control programmes of P. americana, and may help forecast the time of emergence of nymphs of American cockroaches in infested areas.     

In vitro culture of Trichogramma pretiosum on an artificial medium

The composition of an artificial medium and environmental conditions are described for the in vitro rearing of the egg parasite Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). The medium was composed of defined amounts of protein, carbohydrates, lipid, salts, and vitamins, but also contained up to 40% insect hemolymph. The hemolymph was necessary to induce pupation. T. pretiosum eggs were obtained by dissection of Heliothis virescens (F.) (Lepidoptera: Noctuidae) eggs. In vitro reared T. pretiosum were similar in size to H. virescens reared T. pretiosum, and females were fecund.

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Résumé Les oeufs de Trichogramma pretiosum ont été obtenus par dissection d'oeufs d'Heliothis virescens. T. pretiosum Riley (Hymenoptère, Trichogrammatidae) a été élevé avec succès sur un substrat synthétique. Outre des quantités définies de protéines, glucides, lipides, éléments minéraux et vitamines, la ration contenait aussi jusqu'à 40% d'hémolymphe de Manduca sexta. L'hémolymphe était nécessaire pour induire la nymphose. En plus de la nourriture, les conditions d'environnement sont apparues extrêmement importantes pour élever T. pretiosum dans des conditions satisfaisantes. Le contrôle de l'humidité relative, en particulier, était le facteur le plus important. Les adultes produits au cours de cette étude étaient d'apparence normale; ils se sont accouplés sans problèmes, les femelles étaient fécondes et leur taille ne différait pas de celle d'individus élevés sur H. virescens.

     

Effects of temperature on the immature development and emergence of five species of <Emphasis Type="Italic">Trichogramma</Emphasis>

Five constant temperatures between 14 and 30°C were used to evaluate their effect on the development time and adult emergence of five Trichogramma species found parasitizing eggs of the velvetbean caterpillar Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae) on soybeans in subtropical Southern Brazil. Host eggs were parasitized at 20°C and then transferred to the study temperatures to follow development and emergence of parasitoids. All five species were able to develop and emerge within the range of temperatures evaluated, and the effect of temperature on development rates could be described by linear regression. Trichogramma acacioi Brun, Moraes & Soares and T. rojasi Nagaraja & Nagarkatti were the most cold-tolerant species, with lower threshold temperatures of 8.1 ± 0.16°C and 9.2 ± 0.16°C, respectively. Trichogramma atopovirilia Oatman & Platner was the least cold-adapted species, with a lower threshold of 10.2 ± 0.13°C. Degree-day accumulation ranged from 153.8 DD for T. atopovirilia to 190.7 DD for T. acacioi. Adult emergence was higher than 90% for T. atopovirilia and T. pretiosum at all temperatures, whereas T. lasallei Pinto emergence dropped to 71.3% at 14°C and to 58.3% at 26°C, both significantly lower than the emergence of T. pretiosum and T. atopovirilia. Significantly less T. acacioi adults emerged at 30°C than either T. pretiosum or T. atopovirilia. The sex-ratio was not affected within the range of temperatures studied, and varied from 0.65 to 0.88 (female/(male + female)). Differences among Trichogramma spp. densities in the field can be attributed to slower development rates and/or reduced emergence of adults, both at low and high temperatures.

Biological control of Tipula paludosa (Diptera: Nematocera) using entomopathogenic nematodes (Steinernema spp.) and Bacillus thuringiensis subsp. israelensis

Tipula paludosa (Diptera: Nematocera) is the major insect pest in grassland in Northwest Europe and has been accidentally introduced to North America. Oviposition occurs during late August and first instars hatch from September until mid-October. Laboratory and field trials were conducted to assess the control potential of entomopathogenic nematodes (EPN) (Steinernema carpocapsae and S. feltiae) and Bacillus thuringiensis subsp. israelensis (Bti) against T. paludosa and to investigate whether synergistic effects can be exploited by simultaneous application of nematodes and Bti. Results indicate that the early instars of the insect are most susceptible to nematodes and Bti. In the field the neonates prevail when temperatures tend to drop below 10 °C. S. carpocapsae, reaching >80% control, is more effective against young stages of T. paludosa than S. feltiae (<50%), but the potential of S. carpocapsae might be limited by temperatures below 12 °C. Mortality of T. paludosa caused by Bti was not affected by temperature even at 4 °C but the lethal time increased with decreasing temperatures. Synergistic effects of Bti and EPN against T. paludosa were observed in 3 out of 10 combinations in laboratory assays but not in a field trial. The potential of S. carpocapsae was demonstrated in field trials against early instars in October reaching an efficacy of >80% with 0.5 million nematodes m⁻² at soil temperatures ranging between 3 and 18 °C. Results with Bti were strongly influenced by the larval stage and concentration. Against early instars in autumn between 74 and 83% control was achieved with 13 kg ha⁻¹ Bti of 5,700 International Toxic Units (ITUs) and 20 kg ha⁻¹ of 3,000 ITUs. Applications in spring against third and fourth instars achieved between 0 and 32% reduction. The results indicate that application of Bti and nematodes will only be successful and economically feasible during the early instars and that the success of S. carpocapsae is dependent on temperatures >12 °C. Synergistic effects between S. carpocapsae and Bti require more detailed investigations in the field to determine maximal effect.