Significant Difference In Parasitism Research Articles

Changes in Functional and Numerical Responses of the Parasitoid WaspTrichogramma brassicae(Hymenoptera: Trichogrammatidae) Over 45 Generations of Rearing onEphestia kuehniella

AbstractWe assessed the functional and numerical responses of Trichogramma brassicae Bezdenko under long-term rearing (45 generations, G5-G45) on eggs of a common factitious host, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Under such long-term mass rearing, the function response of this parasitoid shifted from Type III (from G5 to G20) to Type II (from G25 to G45). The maximum attack rate (T/Th) (33.62 hosts/day) and the shortest handling time (0.7138 ± 0.0272 h) were recorded in G5. Also, G45 had the lowest attack rate (21.67 hosts/day) and longest handling time (1.1076 ± 0.0689 h). The handling time increased gradually over the generations (P reg <0.01, R2 = 0.903). The number of eggs laid by the parasitoid increased significantly with increased host density, but reached a plateau at very high densities. While no significant differences in daily parasitism were observed over 45 generations at densities of 2, 4, 8, and 16 available host eggs per wasp, there were significant differences in parasitism at host densities of 32, 64, and 128 eggs per wasp. T. brassicae females were more active and foraged more frequently in earlier generations (G5 to G20), which allowed wasps to parasitize more E. kuehniella eggs compared to later generations. Also, continuous mass rearing of T. brassicae negatively affected foraging behavior and the quality of wasps after G20. However, rejuvenation of the colony by adding field-collected parasitoids or rearing wasps on more suitable factitious hosts is strongly recommended to lower the negative effects of long-term mass rearing on quality of this parasitoid.

Host instars preference, density-dependent parasitism and behavioral perspective of parasitoids (Aphidius colemani, Aphidius matricariae and Aphelinus abdominalis) in Aphis glycines and Aphis gossypii

Three parasitoid species Aphidius colemani, Aphidius matricariae (Hymenoptera: Braconidae) and Aphelinus abdominalis (Hymenoptera: Aphelinidae) were evaluated concerning their parasitism potential in two aphid species, Aphis glycines and Aphis gossypii (Hemiptera: Aphididae). The feeding of these two aphid species, even at low sums, can significantly damage photosynthesis and is found to transmit many kinds of plant viruses, which impact potential adverse effects on the plants. The overall parasitization on all nymphal ages in As. glycines was accomplished by Ad. colemani (60.50%), Ad. matricariae (49.16%) and Al. abdominalis (40%), while in As. gossypii parasitism exhibited by Ad. colemani (79.48%), Ad. matricariae (65.33%) and Al. abdominalis (58.83%). Aphelinus abdominalis exhibited the lowest parasitism in both given species as hosts. Significant differences in parasitism of different parasitoids and host species were observed. Concerning the preference of nymphal instars, we found that parasitoids species prefer to parasitize 1st- 4th instars in As. gossypii while in As. glycines 2nd, 1st, 3rd and 4th. Our results showed that the parasitism increases with the increase of parasitoid numbers and hosts densities.

Parasitism and Predation on Sentinel Egg Masses of Three Stink Bug Species (Hemiptera: Pentatomidae) in Native and Exotic Ornamental Landscapes.

This study evaluated parasitism and predation on sentinel egg masses of three stink bug species, the spined soldier bug, Podisus maculiventris (Say), the brown stink bug, Euschistus servus (Say), and the invasive brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), in ornamental landscapes composed of either native or exotic plants. This study also compared the species composition of parasitoids attacking two native stink bug species (P. maculiventris and E. servus) with those attacking the invasive BMSB on the same tree species in the same habitat. Overall, egg parasitism and predation were much higher on the two native stink bug species compared with BMSB, with an average parasitism rate of 20.6% for E. servus, 12.7% for P. maculiventris, and only 4.2% for H. halys and an average predation rate of 8.2% for E. servus,17.7% for P. maculiventris, and 2.3% for H. halys. Egg predation was also significantly higher on P. maculiventris than on E. servus eggs. Eight parasitoid species attacked sentinel stink bug eggs in the ornamental landscaped plots. Trissolcus euschisti (Ashmead) (Hymenoptera: Scelionidae) was the predominant parasitoid for all three stink bug species. There were no significant differences in parasitism and predation rates on any of the stink bug species between native and exotic plots. Therefore, there is no evidence that ornamental landscapes composed of native plants increased parasitism or predation rates of sentinel egg masses of two native stink bug species or the invasive BMSB, compared with those composed entirely of exotic plants.

Influence of Density on Interspecific Competition Between Spathius galinae (Hymenoptera: Braconidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae), Larval Parasitoids of the Invasive Emerald Ash Borer (Coleoptera: Buprestidae).

The outcomes of interspecific interactions between parasitoids depend on a variety of factors. Understanding the influence of these factors is important for classical biological control, where the success of parasitoid releases partly depends on interactions with native and other introduced species. However, results from laboratory experiments may not always reflect those in the field, as densities may be artificially inflated. To mitigate this problem, we examined the effects of multiple densities on interspecific competition between two larval parasitoids of emerald ash borer (Agrilus planipennis Fairmaire): Spathius galinae Belokobylskij and Tetrastichus planipennisi Yang. Parasitoid species were housed individually or together at two different densities, and we measured the effects on percent parasitism and progeny production, before calculating the interaction strengths. We found no significant effects of parasitoid density on percent parasitism, but the effect of competition on parasitism generally was reduced at lower densities. However, there were significant differences in parasitism by species, with S. galinae parasitizing more larvae than T. planipennisi. There were also no significant effects of parasitoid density on the number of progeny produced by each species, though the effect of competition on progeny production was greater at higher densities. Similarly, though, there were significant differences between species in the number of progeny produced. Specifically, T. planipennisi consistently produced larger broods than S. galinae. Our findings complement existing research suggesting that competition between these two species in the field will likely be negligible.

Occurrence, Seasonal Abundance, and Superparasitism of Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) as an Egg Parasitoid of the Spotted Lanternfly (Lycorma delicatula) in North America

The occurrence of egg parasitoid Ooencyrtus kuvanae (Howard) (Hymenoptera: Encyrtidae) on its new host, the spotted lanternfly (Lycorma delicatula (White) (Hemiptera: Fulgoridae)), was surveyed at 4 study plots in 2016 and 10 additional plots in 2017 in Pennsylvania through field collection and laboratory incubation. O. kuvanae adults were found on L. delicatula egg mass surfaces at two plots (ODSouth and Lutz) in 2016, but at none in 2017. The results of laboratory incubation showed that O. kuvanae adults were only recovered from host eggs collected at plot ODSouth in 2016, with adults emerging between 22 April and 2 May 2016 at 22 ± 1 °C, 40% ± 5% relative humidity (RH), and a 16:8 h photoperiod (light/dark). The overall parasitism at this study plot was 6.0% by egg mass and 1.2% by egg. Two oviposition sites contained parasitized L. delicatula eggs, with 12.3% (9.5–15.0%) host egg masses and 3.1% (1.3–5.0%) host eggs utilized by the parasitoid. O. kuvanae parasitism by egg was significantly higher on oviposition site ODSouth #7 than on ODSouth #8. No O. kuvanae adults were reared out of field-collected host eggs from the 10 plots in 2017. Seasonal abundance and superparasitism of O. kuvanae was examined at plot ODSouth in 2017. O. kuvanae-parasitized L. delicatula eggs were found on all four oviposition sites based on field monitoring of parasitoid adult emergence, resulting in a parasitism of 35.4% (18.8–55.6%) by egg mass and 2.2% (0.5–3.9%) by egg. No significant difference in parasitism by egg was observed among oviposition sites. O. kuvanae adults emerged in the field between 2 May and 1 June 2017. Superparasitism was confirmed for O. kuvanae on L. delicatula eggs based on parasitoid production (1.0–3.3 adults/parasitized egg) and adult exit holes (1–3 exit holes/parasitized egg). As the first parasitoid recorded from L. delicatula in North America, O. kuvanae has the potential to become an important biological control agent for L. delicatula in North America, with its well-synchronized life history in the spring, century-long field establishment, superparasitism, and female-biased progeny population. L. delicatula complements the gypsy moth well as an alternative host for O. kuvanae in the field.

Evaluation of a banker plant system for biological control of Bemisia tabaci (Hemiptera: Aleyrodidae) on tomato, using two aphelinid parasitoids under field-cage conditions

ABSTRACTThis study evaluated the potential of two aphelinid parasitoids, Encarsia sophia (Girault & Dodd) and Eretmocerus hayati (Zolnerowich & Rose) to control the sweetpotato whitefly Bemisia tabaci, (Gennadius) using a banker plant system over two consecutive years. The parasitism rates of both parasitoids on a tomato (Solanum lycopersicum L.) crop were determined using melon, Cucumis melo L. (Cucurbitaceae) and castor bean, Ricinus communis L. (Euphorbiaceae), as banker plants, respectively. The emergence rates of Er. hayati and En. sophia parasitoids from parasitised whiteflies on both banker plants exceeded 90% and 85%, respectively, which is 17–20 percentage points higher than that on the pupal card under field cage conditions. Parasitism (%) on banker plants was significantly higher for both parasitoids in the third week after release as compared to adult releases in the first year, reaching 15.2 ± 1.3 and 24.0 ± 1.4% for En. sophia and Er. hayati, respectively. However, no significant difference in parasitism (%) was observed between banker plant and pupal card release treatments in the second year. The combined release of the two parasitoids during the second year clearly showed a continuous increase in parasitism, which was higher than parasitism in the single parasitoid-release treatments by the 4th week after release. Whitefly populations were significantly lower in all parasitoid-release treatments than in the no-release control by 4–6 weeks into the study period in the second year, while no other significant differences were observed between treatments in either year. This study found that both banker plants efficiently supported populations of both parasitoids and improved their emergence compared to the pupal card.

Occurrence of Tomicobia seitneri (Hymenoptera: Pteromalidae) and Ropalophorus clavicornis (Hymenoptera: Braconidae) in Ips typographus adults (Coleoptera: Curculionidae: Scolytinae) from Austria, Poland and France

AbstractThe presence of hymenopteran parasitoids in adult

Natural biological control of Halyomorpha halys by native egg parasitoids: a multi-year survey in northern Delaware

Halyomorpha halys (Stal) is a highly polyphagous plant pest native to eastern Asia. Since its accidental introduction to the USA in the mid-1990s, it has spread across North America and caused serious economic damages. Chemical control has been a widely applied management strategy which is not sustainable on a long-term basis. A nine-year survey using sentinel and naturally laid H. halys was conducted to investigate the extent of natural biological control by parasitoids in managed and non-managed landscapes in northern Delaware, USA. Naturally laid egg masses of native pentatomids were collected to compare the resident parasitoid complex to the one attacking H. halys eggs. Mean parasitism rates of sentinel eggs were below 6% in any given year of the survey with a grand mean of 1.79%. Parasitism of naturally laid H. halys eggs was higher than that of sentinel eggs, but there was no significant difference in parasitism between years and the grand mean was 4.31%. Parasitoid species richness on sentinel and naturally laid H. halys eggs was similar but both were lower than the richness on native pentatomid eggs. H. halys eggs were parasitized by eight species in the genera Anastatus, Trissolcus, Telenomus, and Ooencyrtus. The level of parasitism by native egg parasitoids is insufficient to provide long-term control of H. halys. Trissolcus japonicus (Ashmead), an Asian egg parasitoid that has been recovered in the USA in several locations since 2014, may be the most promising candidate for long-term biological control of H. halys.

The Effects of Temperature and Host Age on the Fecundity of Four Trichogramma Species, Egg Parasitoids of the Cnaphalocrocis medinalis (Lepidoptera: Pyralidae).

The Cnaphalocrocis medinalis (Guenée) is one of the most important rice pests in Asia and is difficult to control by chemical insecticides due to its rapid development of resistance. To screen potential species for biological control of C. medinalis, we investigated the effects of temperature (20, 24, 28, 32, and 36 °C) and host age (1-, 2-, 3-, and 4-d-old) on the fecundity of four Trichogramma spp. on C. medinalis eggs. Our results indicated that C. medinalis eggs were acceptable to T. japonicum, T. chilonis, T. dendrolimi, and T. ostriniae, though no eggs were parasitized at 36 °C. There were no significant differences in parasitism among the four Trichogramma species under the tested temperature regions, except at 20 °C where parasitism by T. japonicum was significantly higher than that by T. chilonis and T. ostriniae. However, T. japonicum had significantly more progeny than the other three Trichogramma species at 32 °C. All four Trichogramma species performed well on 1-, 2-, and 3-d-old C. medinalis eggs, but parasitism on 4-d-old eggs was significantly reduced. Trichogramma japonicum parasitized the highest number of C. medinalis eggs on different aged hosts and had more progeny than the other Trichogramma species, especially on 3-d-old hosts. In conclusion, T. japonicum exhibited better performance on C. medinalis eggs than the other three Trichogramma species and could be considered as our most suitable Trichogramma candidate for control of C. medinalis.

Emergence of the Zoonotic Biliary Trematode Pseudamphistomum truncatum in Grey Seals (Halichoerus grypus) in the Baltic Sea

The biliary trematode Pseudamphistomum truncatum parasitizes a wide range of fish-eating mammals, including humans. Here we report the emergence of this parasite in grey seals (Halichoerus grypus) in the Baltic Sea. One hundred eighty-three of 1 554 grey seals (11.9%) examined from 2002–2013 had detectable hepatobiliary trematode infection. Parasite identification was confirmed as P. truncatum by sequencing the ITS2 region of a pool of five to 10 trematodes from each of ten seals collected off the coast of seven different Swedish counties. The proportion of seals parasitized by P. truncatum increased significantly over time and with increasing age of seals. Males were 3.1 times more likely to be parasitized than females and animals killed in fishery interactions were less likely to be parasitized than animals found dead or hunted. There was no significant difference in parasitism of seals examined from the Gulf of Bothnia versus those examined from the Baltic Proper. Although the majority of infections were mild, P. truncatum can cause severe hepatobiliary disease and resulted in liver failure in at least one seal. Because cyprinid fish are the second intermediate host for opisthorchiid trematodes, diets of grey seals from the Baltic Sea were analysed regarding presence of cyprinids. The proportion of gastrointestinal tracts containing cyprinid remains was ten times higher in seals examined from 2008 to 2013 (12.2%) than those examined from 2002 to 2007 (1.2%) and coincided with a general increase of trematode parasitism in the host population. The emergence and relatively common occurrence of P. truncatum in grey seals signals the presence of this parasite in the Baltic Sea ecosystem and demonstrates how aquatic mammals can serve as excellent sentinels of marine ecosystem change. Investigation of drivers behind P. truncatum emergence and infection risk for other mammals, including humans, is highly warranted.

Biological control of sentinel egg masses of the exotic invasive stink bug Halyomorpha halys (Stål) in Mid-Atlantic USA ornamental landscapes

Biological invasions have far reaching effects on native plant and arthropod communities. This study evaluated the effect of natural enemies on eggs of the exotic invasive brown marmorated stink bug Halyomorpha halys (Stål) in experimental plots comprising species pairs of 16 ornamental trees and shrub genera from either Eurasia or North America and in wooded areas adjacent to the plots. Sentinel egg masses were placed on leaves of Acer, Cercis, Hydrangea, and Prunus in the plots and in seven genera of trees and shrubs in adjacent woods. Overall, rates of parasitism and predation in experimental plots were low, accounting for only 3.8% and 4.4% of egg mortality, respectively. There were no significant differences in parasitism and predation rates between native or exotic plots or between plants of different genera. In 2015, predation was significantly higher in the experimental plots than in the wooded sites, but parasitism was significantly higher in the wooded sites. In the experimental plots, seven native and one exotic parasitoid species attacked sentinel egg masses. Six native parasitoid species attacked sentinel egg masses in the wooded sites. Parasitoids in the genus Trissolcus were more likely to attack egg masses in exotic plots than in native plots. There is no evidence that native natural enemies attacking eggs of the exotic BMSB were more prevalent in landscapes with native ornamental trees and shrubs than those with exotic trees and shrubs.

Enteroparasitismo en indígenas Terena en el estado de Mato Grosso do Sul, Brasil

Considering that intestinal protozoans and helminths infect more than half of the world population, with high prevalence in the poorest regions, the objective of this study was to conduct parasitological research among indigenous Terena people established in the state of MatoGrosso do Sul. An inquiry was performed to find the incidence of parasitism in these communities. 134 aliquots of feces from individuals of the indigenous community were examined. Samples were conserved in Merthiolate-iodine-formol solution (MIF). The laboratory exams were carried out using the techniques of Hoffman, Pons and Janer; Willis and Kinyoun. We identified infections of nematode helminths of the species Ascaris lumbricoides, Ancylostomidae, Enterobius vermicularis, Strongyloides stercoralis, and Trichuris trichiura; and cestodes of the species Hymenolepis nana and Taenia spp. Also found were the protozoan species: Cryptosporidium spp., Giardia lamblia, Endolimax nana, Entamoeba coli, and Entamoeba histolytica. 23.1 % of the samples studied were negative. Of the 76.9 % of samples with parasites, there were non-statistically significant differences in parasitism between men and women examined between 1 and 33 years-of-age. There were also no significant differences between monospecific parasitism and with concurrent species. In terms of parasitic diversity, seven species of nematode and cestodes helminths were found along with five species of Archamoebae protozoa: flagellates and enterozoans. These results were the basis for orientation and appropriate drug intervention and reveal the need for the implementation governmental, social and educational measures to improve the living conditions of that community.

Parasitism and Suitability of Different Egg Ages of the Leguminivora glycinivorella (Lepidoptera: Tortricidae) for Three Indigenous Trichogramma Species

Pod borers are economically important soybean pests in temperate and tropical regions. However, the biological control of these pests using their natural insect enemies has been poorly studied to date. Indigenous natural populations of three Trichogramma (Hymenoptera: Trichogrammatidae) species, Trichogramma chilonis Ishii, Trichogramma ostriniae Pang & Chen, and Trichogramma leucaniae Pang & Chen, were collected from Leguminivora glycinivorella (Matsumura) (Lepidoptera: Tortricidae) eggs in soybean fields in China. In this study, we compare the parasitic capacities and suitabilities of three indigenous Trichogramma species on L. glycinivorella eggs at various ages. Host eggs of all ages were accepted by T. chilonis, T. ostriniae, and T. leucaniae. T. chilonis tended to parasitize 0-2-d-old eggs more than 3-4-d-old eggs. There were no significant differences in parasitism between the 0-2-d-old eggs and the 1-4-d-old eggs for T. ostriniae and T. leucaniae. For eggs at various ages, T. chilonis parasitized the smallest number of eggs, while T. leucaniae and T. ostriniae exhibited similar parasitic capacities. With 0-d-old host eggs, T. ostriniae developed over the longest time period (8.7 d), and T. leucaniae produced the most female progeny (87.9%). Both T. leucaniae and T. ostriniae had similar developmental times, survival rates and percentages of female progeny with 1-3-d-old eggs. These results show that T. leucaniae can parasitize host eggs at varying ages with the best development and suggest that it may be a valuable biological control agent for soybean pod borers.

Effect of <i>Epichlo</i> endophyte strains in <i>Lolium</i> spp cultivars on Argentine stem weevil parasitism by <i>Microctonus hyperodae</i>

This paper reports on an extensive field investigation conducted at Lincoln during the 20142015 summer/early autumn This aimed to assess the effects of a range of novel Epichlo endophytes when present in different cultivars of Lolium spp on parasitism rates by the biological control agent Microctonus hyperodae in Listronotus bonariensis (ie the Argentine stem weevil) Results for the entire summer and including all treatment combinations did not find any significant differences in parasitism in L bonariensis populations However in the early autumn independent of the endophytes present significantly higher levels of parasitism were found in a tetraploid Lolium multiflorum cultivar and a tetraploid L perenne selection compared to the L perenne cultivars Whether this finding has any bearing on a possible mechanism of weevil resistance is discussed

Host stage preference ofDolichogenidea tasmanica(Cameron, 1912) (Hymenoptera: Braconidae), a parasitoid ofEpiphyas postvittana(Walker, 1863) (Lepidoptera: Tortricidae)

Epiphyas postvittana (Walker, 1863), or light brown apple moth (LBAM), is a highly polyphagous native Australian species and a major insect pest in Australian vineyards. Dolichogenidea tasmanica (Cameron, 1912) is the most abundant parasitoid of the larval stages of LBAM. The prime objective of our study was to determine the parasitism success of D. tasmanica on different larval stages of E. postvittana. Additionally, we aimed to find out if larval head capsule width could be used to determine the instar number by examining the variability in head capsule size of each instar of LBAM and the effect of rearing temperature on larval head capsule size. To determine which of the first three larval stages of LBAM parasitised is most effectively by D. tasmanica, choice and no-choice tests were conducted in a wind tunnel. Head capsule widths varied with rearing temperature, especially in the final fifth or sixth instar. We showed that the ranges of head capsule widths overlaps between successive instars three through six, which makes it impossible to distinguish these instars of LBAM using head capsule size alone. We showed that first, second and third instars of LBAM are parasitised by D. tasmanica. No-choice and choice tests revealed that there are significant differences in parasitism among the three susceptible instars, with the highest percentage of parasitism found in second instars in no-choice and choice tests (65.1% and 65.8%, respectively) compared with first instars (61.1% and 45.1%) and third instars (27.3% and 37.5%). Wasps developed faster in third instars, but the wasp female's size was not significantly different among the instars attacked. These data confirm that D. tasmanica is capable of parasitising early larval instars, which is important for minimising damage through biological control.

Higher gregarine parasitism often in sibling species of host damselflies with smaller geographical distributions

1. This study investigated inter‐specific variation in parasitism by gregarines (Eugregarinorida: Actinocephalidae), among sibling species of damselflies (Odonata: Zygoptera), in relation to relative size of geographical ranges of host species.2. Gregarines are considered generalist parasites, particularly for taxonomically related host species collected at the same sites or area. Prevalence and median intensity of gregarine parasitism was obtained for 1338 adult damselflies, representing 14 species (7 sibling species pairs) across 3 families within the suborder Zygoptera. Damselflies were collected at three local sites in Southeastern Ontario, during the same periods over the season.3. Five out of seven species pairs had significant differences in parasitism between sibling species. The less widespread host species was the more parasitised for three species pairs with significant differences in gregarine prevalence, and for two species pairs with differences in median intensity. The more widespread host had a higher intensity of infection as expected, in two species pairs.4. Future studies on ecological determinants of parasitism among related species should examine robust measures of abundance of species and representation of species regionally.

Biology of the Adult Stage of Ufens principalis (Hymenoptera: Trichogrammatidae), an Egg Parasitoid of Homalodisca spp.(Hemiptera: Cicadellidae) in Southern California

Abstract Aspects of the biology of the adult stage of Ufens principalis Owen (Hymenoptera: Trichogrammatidae), an important parasitoid of Homalodisca (Hemiptera: Cicadellidae) eggs in southern California, were studied. The field-based sex ratio of U. principalis was significantly different from 1:1 and was female biased (62% females). Females and males did not differ significantly in size based on measurements of head width and hind tibia length, and these two variables were highly correlated. There was a significant effect of female age on egg load. Females aged 1, 4, and 5 d had significantly higher egg loads than freshly emerged females. There was also a significant positive linear relationship between egg load and hind tibia length. Egg load averaged 37.9 ± 1.1 eggs. Eggs, which measured 207.8 ± 12.2 µm in length, were elliptical with an anterior nipple-shaped constriction. The longevity of adults was significantly affected by temperature and food (1:1, honey/water). Food had a greater effect in prolonging life as temperature decreased from 35.0 to 10.0°C. The most long-lived adults were fed on honey and kept at 10.0°C (20.2 ± 3.3 d). The rate of parasitism was significantly affected by host age, being significantly higher for 0-h-old eggs than for 12-24-h-old host eggs. There was no significant difference in parasitism between 0-h- and 0-6-h-old eggs and between 0–6 and 12-24-h-old eggs.

Parasitic and Phoretic Mites Associated with Neotropical Harvestmen from Trinidad, West Indies

AbstractLarval erythraeid mites are common ectoparasites of harvestmen (Opiliones). However, interactions between these mites and hosts in tropical environments have received little attention. In this study, we examined the prevalence and intensity of mite infestations for Neotropical harvestmen from the Caribbean island of Trinidad. Overall, the prevalence of infestation was 9.9%, with significant interspecific variation in the intensity of mite infestation and significant differences in parasitism of hosts between habitats. Harvestmen collected from lowland, crappo-cocorite forest exhibited the highest infestation rates. In our samples, the intensity of infestation varied from 1 to 17 mites per host. Examination by scanning electron microscopy revealed that harvestmen were infested by two taxa of mites, a species of Leptus and another unidentified erythraeid species. Our observations represent the first host records for erythraeid mites parasitizing harvestmen from the families Cranaidae and Manaosbiidae. Mites were found to attach preferentially to the tibia and femur of the leg (175 of 178 observations). In general, the harvestmen of Trinidad exhibited mite parasitism in a fashion similar to temperate species with respect to site of attachment and prevalence and intensity of mite infestation. In the field, we also collected an adult Cynortula sp. (Cosmetidae) that was transporting 30 gravid adults of an oribatid mite (Acariformes, Oribatida, Mixonomata). Cases of mite phoresy upon harvestmen are rare, with our observation representing the first report of phoresy by an oribatid mite upon a harvestman and the first documentation of mite phoresy upon harvestmen in the Caribbean.

Hyperparasitism by an exotic autoparasitoid: secondary host selection and the window of vulnerability of conspecific and native heterospecific hosts

Abstract Encarsia transvena is an ‘autoparasitoid’ in the hymenopteran family Aphelinidae. In this species, female eggs are laid in whitefly nymphs. Male eggs are laid externally on immature parasitoids enclosed within the whitefly integument, either their own species, or other primary parasitoids. We explored parasitism by E. transvena of conspecific female immatures and those of a native primary parasitoid, Eretmocerus eremicus, in laboratory experiments. In the first experiment, female E. transvena were offered different combinations of two stages of E. transvena (late larvae – prepupae (ET2), and early pupae (ET3)), and one stage of E. eremicus (prepupae – early pupae (EE2)) in paired choice tests. The results indicated very little parasitism of ET3 relative to the host it was paired with, either EE2 or ET2. However, when EE2 was offered with ET2, there was no statistically significant difference in parasitism. In a no‐choice experiment in which oviposition patterns and male progeny development were examined in four stages of both species of wasp, clear differences were observed between the host species. Only one stage of E. transvena (ET2) was parasitized and supported development of male E. transvena to any significant degree. In contrast, in E. eremicus, EE2, EE3 (red‐eyed pupae), and EE4 (late pupae) were all parasitized, and male E. transvena emerged from all three stages, although fewer males emerged from EE4. In both species, wasp larvae that were still enclosed within the wet whitefly remains (ET1 and EE1) were parasitized at a very low rate. Lastly, an experiment that determined the length of the later developmental stages of E. transvena and E. eremicus suggested that the duration of the period in which E. transvena is susceptible to parasitism by conspecific females is less than half the period of susceptibility of E. eremicus. These results taken together suggest the potential for interference of E. eremicus by E. transvena, but other factors not examined here may also influence the outcome of interactions in the field.

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellen andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.