Influence of prey density, species and developmental stages on the predatory behaviour ofAmblyseius longispinosus (Acari: Phytoseiidae)

The influence of prey density, species and developmental stages on the predatory behaviour ofAmblyseius longispinosus (Evans) was studied. A 24 h exposure revealed that gravid females were more voracious compared to young females. The trends in the number of eggs and larvae consumed by each young and gravid female predator were about the same, showing an increase with density of the red and the yellow strains ofT. urticae levelling off at a prey density of 40 per predator. The highest mean number of eggs consumed in 24 h was 16.7 for the young female and 33.3 for the gravid female, and a mean high of 17 larvae in 24 h for the young female and 27.8 for the gravid female. With adult prey, however, the predators reached satiation point at a lower density of five to ten adult prey per female. In general, the response curves were adequately described by the Holling’s Type II model. Under continuous exposure for five days, a significant reduction in consumption was observed with the gravid female from the second day onwards, to a level similar to the number of eggs and larvae consumed by a young female predator.     

Interactions betweenPleolophus basizonus andLophyroplectus luteator [Hym.: Ichneumonidae], two parasites ofNeodiprion sertifer [Hym.: Diprionidae]

Females ofPleolophus basizonus (Gray.) show a very strong avoidance of cocoonedNeodiprion sertifer (Geoff.) prepupae in which there are eggs, larvae or prepupae ofLophyroplectus luteator (Thunb.). When multiparasitism does occurP. basizonus is the successful competitor but adults are much smaller than those from hosts that were not multiparasitized.     

Characterization and the developmental role of plasma juvenile hormone esterase in the adult cabbage looper,Trichoplusia ni

Juvenile hormone (JH) esterase was characterized from the plasma of adult females of the cabbage looper, Trichoplusia ni, and compared with that present in 4th and 5th instar larvae. Ester hydrolysis was the principal route of JH metabolism. Gel filtration of plasma resolved a single peak of JH esterase which was distinct from that of the α-naphthyl acetate (α-NA) esterase activity. The JH esterase apparent molecular weight was 62,000 in prepupae and virgin, female adults and 69,000 in 2-day-old 4th instar larvae. Broad range isoelectric focusing of plasma of prepupae and adults resolved a major peak of activity at pH 5.5 with a minor peak of activity at pH 6.1 and in 4th instar larvae at pH 5.45 and 5.8, respectively. By this method JH esterase was resolved from the α-NA esterase activity. The plasma of prepupae and adults metabolized JH I at about twice the rate of JH III. JH esterase activity from adult plasma was more stable than the α-NA esterase activity. Adult JH esterase activity was insensitive to inhibition by O,O-diisopropyl phosphorofluoridate in contrast to that of the α-NA esterase activity. Mated females oviposited 8 times more eggs than virgin females to 10 days after emergence. The total haemolymph protein content of virgin females remained high throughout the period of study whereas mated females showed a significant decline beginning on day 4. JH esterase activity remained unchanged in virgins whereas it declined drastically in mated females. The α-NA esterase activity declined to low levels shortly after emergence in both groups. JH and α-NA esterase activity was not affected by the application of the juvenoid, (RS)-methoprene. The present study provides evidence of a functional role for JH esterase in JH metabolism and reproduction in adult T. ni. JH esterases in the adult were identical to that of prepupae by the methods described above.     

Predation byXylocoris flavipes [Hem.: Anthocoridae]: Influence of stage,species and density of prey and of starvation and density of predator

When the efficacy of the predaceous bugXylocoris flavipes (Reuter) was tested in the laboratory as a biological control agent against stored-product insects, it attacked eggs more than larvae, pupae, or adults and early-stage larvae ofTribolium castaneum (Herbst) more than late-stage larvae. The predator also killed more larvae ofT. castaneum than larvae ofAttagenus megatoma (F.). The density of predator and prey regulated the capture rate of the predator. Predation byX. flavipes was uninfluenced by starvation for as much as 96 hr.     

Effect of hosts and parasite density on the egg parasiteTrichogramma pretiosum [Hym.: Trichogrammatidae]

When females ofTrichogramma pretiosum Riley were confined with host eggs at a density of 2/150 eggs, they produced 12 times more female progeny on eggs of potato tuber moth than on eggs ofHeliothis armigera (Hübner) and 13,6 times more on eggs ofSitotroga cerealella (Olivier) than on eggs ofHeliothis. At a density of 4/150 eggs, the correspondent figures were 13 and 8 times. The percentage emergence fromHeliothis eggs was from 0,29 to 0,14 times as great as from tuber moth orSitotroga. From 15 to 140 times more runts were observed amongTrichogramma fromHeliothis eggs than among those from tuber moth eggs and 8 times more thant among those fromSitotroga eggs. This may explain the low recoveries in South Africa ofT. pretiosum in eggs ofH. armigera collected in cotton fields after mass liberation of the parasite. An increase in parasite density from 1/300 eggs to 16/300 eggs resulted in a decrease from 29 to 14 in the hosts parasitised per female, a decrease in the proportion of female progeny from 72 to 39%, a decrease in the female progeny per female from 18 to 4,8, and an increase in the proportion of runts from 2,4 to 12,4%. It is suggested that in mass culture ofTrichogramma unduly high parasite densities should be avoided in order to reduce the effect of mutual interference and raise the output of female progeny.     

Development ofLydina polidoides [Diptera: Tachinidae] in relation to its hostChrysoteuchia topiaria [Lepidoptera: Pyralidae]

Lydina polidoides (Townsend) andChrysoteuchia topiaria Zeller were studied in the laboratory. The rate of development ofC. topiaria from eclosion to the diapausing prepupae was 55 days when larvae were exposed to long daylenghts (16 hr light, 8 hr dark) and 43 days when exposed to short daylengths (12 hr light 12 hr dark.) The same insects exposed to long days emerged as adults in 124 days, whereas those exposed to short days emerged in 156 days because short days prepared the prepupae for diapause but failed to maintain the diapause. When caterpillars (prepupae) ofC. topiaria parasitized by young larvae ofL. polidoides and non-parasitized caterpillars were removed from the field in January and exposed to long days at 21°C,C. topiaria emerged as adults in an average 55 days andL. polidoides in 106 days.Lydina polidoides is therefore univoltine andC. topiaria is probably the primary host of this Tachinid parasite.     

Mediterranean flour moth Ephestia kuehniella eggs and larvae exposed to a static magnetic field and preference by Trichogramma embryophagum

This study investigated the effect of strong magnetic fields as insecticidal activity on Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) larvae and eggs at different stages of development and their preference by the egg parasitoid, Trichogramma embryophagum Hartig (Hymenoptera: Trichogrammatidae). Eggs ranging in age from 24-h to 48-h and 72-h-old and larvae (1 to 2 days) were exposed to 1.4 Tesla (T) magnetic fields from a DC power supply at 50 Hz for different time periods (3, 6, 12, 24, 48 and 72 h). Twelve hours of exposure at 1.4 T was toxic to 24-h-old eggs of E. kuehniella. The 72-h-old host eggs treated with 1.4 T for 6–72 h were not significantly preferred by T. embryophagum. The magnetic field was toxic to 24-h-old eggs of E. kuehniella exposed to 1.4 T for 12. The treatment of magnetic fields on the 72-h-old host egg with 1.4 T at 6–72 h was not significantly preferred by T. embryophagum. Magnetization of 24-h-old eggs of E. kuehniella for 3 h could be effectively used with T. embryophagum as sterilised host eggs. These eggs were markedly preferred by T. embryophagum. The LT₅₀ and LT₉₉ values of magnetic fields at different egg stages of E. kuehniella, and larvae were measured. A level of 1.4 T at 72 h completely prevented the development of the larvae. There was no significant effect on larval survival at 1.4 T at 48 and 72 h. Increasing magnetic fields exposure times for eggs that were 24-h, 48-h and 72-h-old prevented larval emergence and increased their mortality rate. Consequently, magnetic fields could be used in controlling stored-product pest eggs and larvae of E. kuehniella.     

Seasonal development of the lacewing Chrysopa dorsalis Burmeister (Neuroptera, Chrysopidae) in the forest-steppe zone of Russia

Seasonal adaptations of Chrysopa dorsalis Burmeister were studied in Belgorod Province of Russia (50°N, 36°E). It was found that in the forest-steppe zone two generations may be produced, but from 76 to 100% of the prepupae of the first generation entered diapause, about 40% of them having an obligate diapause. In the rest of the population, seasonal development was controlled by photoperiod and temperature. The critical day length was about 17 h at 20°C. Some prepupae were found to require two or three years to complete the diapause. This prolonged diapause seems to be a permanent element of the life cycle of the studied species. The proportion of the prepupae that remain in diapause after the first winter positively correlated with the percentage of diapausing prepupae of the first generation in the previous season (r = 0.8). The offspring from eggs laid by females simultaneously collected under the natural conditions emerged in successive years, and the tendency to enter a long-term diapause was not inherited. The rate of the larvae development and the prepupae weight were not different in individuals which had one-year-long and prolonged diapause. However, the weight loss due to dehydration and respiration during the first winter was slightly lower in the prepupae with the prolonged diapause. The expression of the prolonged diapause was independent of the photoperiod during the diapause induction, but it was increased at a high temperature (28°C). Probably, the prolonged diapause increases polymorphism of local Ch. dorsalis populations, ensuring their survival under unpredictable conditions.     

Development of the bitterling,Tanakia tanago (cyprinidae), with a note on minute tubercles on the skin surface

The development of eggs and larvae and minute tubercles on the skin surface in larvae ofTanakia tanago were observed. The eggs began to hatch approximately 52 hours after insemination and the larvae reached free-swimming stage 19 days after hatching at water temperature of 22±1°C. The egg and larval development and minute tubercles on the skin surface in larvae of this species were similar to those ofAcheilognathus lanceolata andA. limbata. However,T. tanago was distinguishable in egg and larval development fromA. lanceolata andA. limbata by the following characters: the perivitelline space was narrower, embryonic and larval development was faster, and minute tubercles on the skin surface of the anteriormost parts of the yolk sac, and of the body and head were hemispheric in shape. From these characters,T. tanago is considered to be more specialized thanA. lanceolata andA. limbata.     

Phenology, population trend and natural enemies ofAleurothrixus floccosus (Hom.: Aleyrodidae) at a newly invaded area in Athens, Greece

Aleurothrixus floccosus (Homoptera: Aleyrodidae) first invaded eastern urban areas of Athens, Greece, in May 1991. At Zographou, Athens, in 1992–1994, most overwinteringA. floccosus nymphs were of the 3rd and 4th instars, and pupae; during other periods of the year, all developmental instars were found, at fluctuating rates. In 1993, peaks in the numbers of eggs laid coinciding with sharp increases in percentage of 1st instar nymphs found permitted the distinction of 6 overlapping generations. High densities ofA. floccosus infesting citrus in autumn 1992, in the range of 9.1–10.9 nymphs/cm² leaf surface, were brought under control by autumn 1993, with maximum densities of 1.1–1.7 nymphs/cm². This reduction is attributed mostly to the action of the introduced parasitoidCales noacki (Hymenoptera: Aphelinidae), released 3 km from Zographou in 1992 and at Zographou itself in 1993. No indigenous parasitoid was ever found parasitizingA. floccosus. The first record ofClitostethus arcuatus (Coleoptera: Coccinellidae) in Greece is reported. In summer 1992, eggs larvae and adults ofC. arcuatus were noticed on citrus leaves infested withA. floccosus at Zographou. From 1992 to 1994, the adults were often detected in field samplings and on yellow sticky traps. C. arcuatus adults and larvae were successfully reared, under optimal laboratory conditions, on eggs and early-instar nymphs ofA. floccosus and on eggs ofAnagasta kuehniella (Lepidoptera: Pyralidae), but the adults did not reproduce.     

Contest competition inDrosophila subobscura

The role of larval intraspecific competition in laboratory populations ofDrosophila subobscura was investigated. Mortality is density-independent during the first 3 days after hatching but becomes density dependent as development proceeds to pupation. Although total biomass per patch was independent of initial egg density, competition betweenDrosophila larvae leads to the formation of smaller pupae. This resulted in a population that was dominated by suppressed individuals. Development rate ofD. subobscura larvae was not affected by high larval densities. Smaller pupae give rise to females with fewer eggs in their ovarioles. A simple simulation model, predicting the effects of intraspecific competition on the fecundity of the nextDrosophila generation is described.     

Interspecific competition betweenDrosophila melanogaster andDrosophila simulans

Summary The number of eggs laid in aDrosophila culture and the survival of these eggs may depend on the number of larvae that are still inhabiting or that have already used the culture medium.A known average number ofD. simulans st larvae (designated original inhabitants) were introduced into culture vials by allowing adults to lay for 24 h (low density) or 48 h (high density). On each day for 14 days, adults of three competitor strains (D. melanogaster Or-R-C, D. melanogaster yw andD. simulans st) were added to different samples of these vials and allowed to lay for 24 h. The numbers of effective eggs (eggs expected to be laid less those withheld, cannibalised or buried) produced by competitor strains were estimated from adult emergences. Survival of original inhabitant larvae to the adult stage also was measured.At the lower density of original inhabitants, the mean proportions of effective eggs (number of effective eggs/number of eggs expected in an uninhabited culture) were not significantly different for the three competitor strains. The mean proportions were lower at the higher density (significantly so for the twoD. melanogaster competitors), and at this density, the mean proportion forD. melanogaster yw was significantly less than that forD. simulans st. These results are consistent with a simple egg destruction hypothesis, but suggest thatyw females were retaining more eggs at the higher density.Original inhabitants showed higher survival when at the higher density. Each of the three competitors caused a significantly different reduction in original inhabitant survival, which was directly related to competitor larval activity. Increasing larval activity probably reduced survival of original inhabitants by increasing pupal mortality due to drowning in the medium.Day of introduction of competitors influenced survival of original inhabitants and also the proportion of effective eggs from each competitor. The proportion of effective eggs decreased to the day 5 introduction. From day 5 to day 8, the proportion increased because the original inhabitants were pupating. After day 8, effective egg proportions again decreased, possibly due to inhibition of egg-laying or reduced survival of immature stages.     

菜蛾啮小蜂的生物学及温度对其 种群增长的影响

菜蛾啮小蜂Oomyzus sokolowskii (Kurdjumov) 是小菜蛾Plutella xylostella L. 的一种主要寄生天敌。观察表明,该蜂喜产卵于小菜蛾各龄幼虫,也可产卵于预蛹,进行幼虫至蛹期的跨期聚寄生。每头寄主蛹出蜂多为5～10头,平均7.8头,其中雌蜂占85%～90%。该蜂也可产卵于在小菜蛾幼虫体内寄生的菜蛾绒茧蜂高龄幼虫,故又是小菜蛾的兼性重寄生蜂。在杭州,每年该蜂在田间的活动期为4～10月,10月中下旬陆续以老熟幼虫或预蛹进入休眠越冬,第二年4月陆续羽化并开始产卵寄生。该蜂发育、存活和繁殖的适温范围为20～30℃,低于20℃或高于30℃对其存活不利,但在适温下发育羽化的雌蜂,短时间内在32～35℃高温下仍可大量产卵寄生。在20℃、25℃和30℃下,平均每雌一生可寄生小菜蛾幼虫数分别为3.1、13.2和6.8头,产子蜂数分别为20.5、92.1和504头,内禀增长率分别为0.082、0.240和0.263(雌/雌·天)。     

松突圆蚧花角蚜小蜂的生物学

松突圆蚧花角蚜小蜂Cocvobius azumai Tachikawa是松突圆蚧Hemiberlesla pitysophila Takagi的重要寄生蜂,1987-1989年从日本引入我国广东省。对松突圆蚧花角蚜小蜂的形态、发育、繁殖、成虫寿命和取食寄主行为等生物学特征进行了观察。该蜂的雌性幼虫是松突圆蚧雌蚧的初级内寄生蜂,而雄性幼虫则是次级寄生蜂,重寄生在同种或它种膜翅目的老熟幼虫、预蛹和蛹上。雌雄两性的形态在所有发育阶段均不相同。交配过的雄蜂喜欢寄生产卵初期和盛期的雌成蚧,对巳寄生的寄主具有识别能力。在19.7℃一30.9℃变温条件下每头雌蜂平均产卵14.95粒,约60%的卵是在最初3天内产出。松突圆蚧花角蚜小蜂雌性蜂在21℃,24℃,27℃和30℃时从卵发育到成虫的平均历期分别为41.24,32.60,25.60和23.00天,发育起点温度10.1℃,有效积温448.3日度。该蜂在广东省一年发生。9-10代。     

Potential ofGeocoris punctipes [Hemiptera: Lygaeidae] andNabis spp. [Hemiptera: Nabidae] as predators ofEpilachna varivestis [Coleoptera: Coccinellidae]

Predation byGeocoris punctipes (Say) andNabis spp. onEpilachna varivestis Mulsant was studied in the laboratory at 26.7°C and in field cages containing soybeans. Both predator groups fed uponE. varivestis eggs, 1st, 2nd and 3rd stage larvae, but not upon 4th stage larvae, pupae, or adults. G. punctipes females produced significantly fewer eggs when fedE. varivestis eggs or 1st stage larvae than those fedGalleria mellonella (L.). Longevity of maleG. punctipes was significantly reduced when fedE. varivestis eggs; however, female longevity was not affected. Results from field cage tests indicated bothG. punctipes andNabis spp. could significantly reduce the density ofE. varivestis.     

Development of the bitterling,Paracheilognathus himantegus (Cyprinidae), with a note on minute tubercles on the skin surface

The development of the eggs and larvae and minute tubercles on the skin surface ofParacheilognathus himantegus larvae were observed. The egg began to hatch approximately 68 hours after insemination and the larvae reached the free-swimming stage 23 days after hatching at water temperature of 22±1°C. The larval development and minute tubercles on the skin surface of this species were similar to those ofAcheilognathus lanceolata, A. limbata, A. signifer andTanakia tanago. However, the shape of the ripe eggs ofP. himantegus differed from those of the four species. As regards the shape of eggs, there was a common characteristic amongP. himantegus, Rhodeus uyekii andA. limbata from Korea. As regards larval development,P. himantegus had two characters also found inRhodeus. These facts seem to suggest thatP. himantegus is closely related toA. lanceolata, A. limbata, A. signifer andT. tanago but is more specialized than these four species, except forA. limbata from Korea.     

Predation rates of Neoseiulus womersleyi (Schicha) and Euseius ovalis (Evans) feeding on tetranychid mites (Acari: Phytoseiidae,Tetranychidae)

Predation rates of Neoseiulus womersleyi and Euseius ovalis feeding on eggs, larvae, or protonymphs of Tetranychus urticae, Tetranychus kanzawai, or Oligonychus mangiferus were measured in a chamber at 25 °C. N. womersleyi immatures consumed 9.73 T. urticae eggs, 13.53 larvae, or 11.57 protonymphs, while gravid females consumed 12.13 T. urticae eggs, 14.37 larvae, or 12.07 protonymphs daily. Female N. womersleyi consumed a total of 218.12 T. urticae eggs, 260.85 larvae, or 222.33 protonymphs, while male N. womersleyi consumed a total of 96.39 T. urticae eggs, 112.23 larvae, or 99.65 protonymphs. When O. mangiferus larvae or protonymphs were offered to E. ovalis, immatures consumed 18.57 larvae or 17.47 protonymphs. Gravid females consumed 16.83 larvae or 12.83 protonymphs daily, with a total of 330.68 larvae or 252 protonymphs. Adult E. ovalis males consumed fewer O. mangiferus larvae (107.69) or protonymphs (91.51) than females. Conversion rate of predation to reproduce was expressed as “Food–reproduction exchange rate” of N. womersleyi was lower on T. urticae than on T. kanzawai. E. ovalis showed a higher food–reproduction exchange rate on O. mangiferus than on T. urticae. The results suggest that N. womersleyi and E. ovalis feed mainly on larvae and protonymphs rather than on the eggs of T. urticae, T. kanzawai, and O. mangiferus. We recommended using T. urticae eggs are suitable food for mass rearing for both N. womersleyi and E. ovalis.     

Parasitism ofTrialeurodes ricini byEncarsia formosa: Level of parasitism,development time and mortality on different host plants

The effects of the host plant on the level of parasitism, development time and mortality ofEncarsia formosa Gahan parasitizing castor whitefly,Trialeurodes ricini Misra were studied. The level of parasitism varied significantly between host plants; ranging from an average high of 13/50T. ricini larvae parasitized per parasitoid per day on aubergine to an average low of 1.6/50 host larvae on potato. Development time ofE. formosa varied according to whitefly host plant; minimum average development time was 17.7 days on cotton. The mortality ofE. formosa was high on all host plants tested, and the type of host plant had no significant influence on mortality. Aubergine proved to be the most satisfactory laboratory plant for rearingE. formosa onT. ricini.     

Micrometeorological factors involved in development and survival of free-living stages of the sheep nematodesHaemonchus contortus andTrichostrongylus colubriformis. A review

Temperature and soil moisture are the most important factors affecting the development and survival ofHaemonchus contortus andTrichostrongylus columbriformis eggs and larvae on pasture. More than half of the eggs develop into infective larvae in the laboratory, but a very low percentage (0.03% forH. contortus) does so on pasture. There is a marked difference betweenH. contortus andT. colubriformis in survival of infective larvae.H. contortus larvae survived in the winter at Urbana poorly, whereasT. colubriformis did well. The former survived better than the latter in the spring and worse in the summer, while both survived equally well in the fall. Technics for larval recovery from pasture are not very efficient. Meteorologic conditions at ground level where the larvae exist are quite different from those in a standard weather shelter 1.6 m above the ground. Bioclimatographs in which mean monthly maximum temperatures are plotted against total monthly precipitation are fairly good in predicting the type of nematode liable to be important in a given region, but they are too simplistic to be relied on for more than approximations.     

Effect of prey density on predaceous efficiency and oviposition ofAgistemus exsertus (Acari: Stigmaeidae)

The oviposition and prey consumption rates ofAgistemus exsertus Gonzalez depend on the number of prey available to the predator. The number of eggs laid by the predator female and the consumption ofTetranychus urticae Koch as prey increased with increasing prey density to maximum averages of 2.3 deposited eggs and 5.8 devoured larvae per day at a prey density of 7 larvae. Higher levels of prey decreased predator oviposition and feeding capacity.