Field and laboratory studies on the timing of oviposition and hatching of the western black-legged tick, Ixodes pacificus (Acari: Ixodidae)

The timing of oviposition and hatching of Ixodes pacificus was investigated in the field and at constant temperatures in the laboratory. Replete females held at temperatures between 9 and 29°C began depositing eggs a mean of 9–70 days after drop off. Egg masses held between 12 and 25°C commenced hatching 25–178 days after the onset of oviposition. Eggs held at 9 or 29°C did not hatch. The lower temperature thresholds for development (LTD) for oviposition and hatching were 6.5 and 9°C, respectively. The number of degree days required for oviposition and hatching was 173 and 588, respectively. Replete females placed in the field on 2 December through to 8 March deposited eggs from 2 February through to 24 April; the eggs commenced hatching between 2 July and 21 August. Unfed larvae from two of 20 egg masses survived through the winter and fed readily when exposed to deer mice (Peromyscus maniculatus) on 22 April. Replete larvae were returned to the field and moulted between 9 and 21 August. Larvae exposed to deer mice in August, 4 weeks after hatching, also fed readily. Although further studies are needed to clarify the timing of nymphal development, the present study suggests that I. pacificus requires more than 1 year to complete its life cycle.     

Effect of different cold storage periods on parasitization performance of Trichogramma cacoeciae (Hymenoptera,Trichogrammatidae) on eggs of Ephestia kuehniella (Lepidoptera,Pyralidae)

The parasitism rates by Trichogramma cacoeciae Marchal (Hymenoptera, Trichogrammatidae) using Ephestia kuehniella Zell. (Lepidoptera, Pyralidae) eggs held at 0, 4 and 8°C and for up to 31 days was measured. Parasitism was lowest on eggs held at 8°C and highest on eggs held at 0°C. The highest parasitism, 97.8%, was measured for parasitoids attacking eggs held for 3 days and stored at 0°C. Parasitism of eggs stored at all three temperatures decreased with increasing duration of storage. The number of T. cacoeciae successfully developing and emerging as adults after storage in E. kuehniella eggs held at 0, 4 and 8°C was measured. Parasitoid emergence was >83% from E. kuehniella eggs stored at 8°C for 3 weeks. Storage at 0°C caused a significant decline in parasitoid emergence after 2 weeks (P<0.05). Storage at 0°C for more than 4 weeks reduced fecundity by 50%. T. cacoeciae parasitized the highest number of E. kuehniella eggs 1 day after adult emergence. The oviposition period lasted 6–7 days, although the parasitoids lived up to 13–14 days. Impact of storage time and temperature on parasitism rates by T. cacoeciae stored while in E. kuehniella eggs was measured. As storage time and temperature increased, subsequent parasitism rates of resulting adult T. cacoeciae decreased. Eggs of E. kuehniella can be stored at 0°C for up to 31 days. Trichogramma cacoeciae developing in eggs of E. kuehniella can be stored at 4°C for up to 5 weeks prior to release.     

Cold storage ofPhytoseiulus persimilis (Phytoseiidae)

Phytoseiulus persimilis is commerelally mass-reared for use as a biological control agent for spider mites, primarilyTetranychus urticae, and cold storage is a potentially valuable aspect of mass-production. Cold storage ofP. persimilis in empty containers was found to be unsatisfactory, but provision of moisture during cold storage greatly increased survival. Provision of food further increased survival even though the mites were stored at temperatures below their threshold for development of 11°C. When food was provided, survival at 7.5°C was 97% after 4 weeks and 80% after 6 weeks. Subsequent longevity and fecundity of mites that survived 8 weeks at 7.5°C was comparable to mites taken directly from mass-rearing cultures. Survival of mites packaged in bran or vermiculite and held at 6°C for 10 days ranged from 75% to 85% and was not decreased by agitating the containers to simulate shipping. However, survival of mites held in bran or vermiculite at 5°C or 8°C for 4 weeks was poor, ranging from 0–19%, due to growth of mould in the media.Phytoseiulus persimilis can be successfully stored for 4 to 6 weeks in containers provisioned only with food and moisture; granular media used for distribution of the mites should be added just prior to shipping.     

Induction of diapausing amictic eggs in Synchaeta pectinata

Amictic females of a clone of S. pectinata from Star Lake (Norwich, Vermont) may produce diapausing as well as non-diapausing (subitaneous) eggs. The proportion of diapausing eggs produced in cultures was unaffected by temperature (12 vs 19 °C) or rotifer population density (minima of 0.33 vs 3 ind. ml^–1) at 19 °C. However, at 19 °C this proportion was higher in cultures maintained at a low food level suppressing reproduction (5 × 10³ cells ml^–1 Cryptomonas erosa) than in those maintained at a high food level (2 × 10⁴ cells ml^–1); the treatment effect was marginally significant (p=0.067). Consistent with the effect of low food availability, a period of starvation was very effective in inducing the development of diapausing eggs. None of 19 females cultured individually from hatching at 19 °C on C. erosa (2 × 10⁴ cells ml^–1) in 1-ml volumes produced any diapausing eggs in 4 days (0 out of 349 eggs), while 13 out of 16 females subjected to a 15-hour starvation period 6 hours after birth produced one or more diapausing eggs during that time (34% of the 158 eggs produced by the 16 females were diapausing). Diapausing eggs produced and left at 19 °C hatched after 4 to 13 days. Those produced in cultures with a low food level took significantly longer to hatch (9.7 days) than those produced in cultures with a high food level (8.1 days) (p=0.022). In natural communities, S. pectinata should be able to respond directly and rapidly to poor food conditions by producing eggs that undergo an obligatory dormant period before resuming development.     

Sucrose and light effects on in vitro cultures of potato,chokecherry and saskatoon berry during low temperature storage

Cultures of potato (Solanum tuberosum) cv. Atlantic, chokecherry (Prunus virginiana L.) cv. Garrington and saskatoon berry (Amelancher alnifolia Nutt.) cv. Northline grown in vitro for 3 weeks at 24/22 °C, 16-h photoperiod, 150 μmol m⁻² s⁻¹ photosynthetic photon flux density (PPFD) mixed fluorescent/incandescent light were stored for 6, 9 and 12 weeks at 4 °C under 0 (darkness) and 3 μmol m⁻² s⁻¹ PPFD (690 nm red light continuous illumination). Growth regulators free MSMO medium either with or without 30 g l⁻¹ sucrose was used to store the cultures. All cultures retained capacity to re-grow after storage. Tested factors, sucrose, light and the length of the storage period had an impact on shoot quality and re-growth capacity of the cultures. For either light treatment sucrose was essential for the low temperature maintenance of vigorous stock plants of potato, if stored for over 6 weeks. Chokecherry and saskatoon cultures stored well without sucrose; although chokecherry benefited from sucrose in the storage medium when the stock cultures were kept at the low temperature for 12 weeks. Low light significantly improved quality of the stored potato cultures, but had very little effect on both chokecherry and saskatoon berry cultures. The woody plant cultures grew during storage, and the longer the stock plants were stored, the more vigorous cultures they generated. The results indicate that growers can successfully use their existing facilities, small refrigerators and coolers with low light intensity, set at 4 °C, for short term storage of potato, chokecherry and saskatoon berry cultures. The potato cultures, which are known to be sensitive to prolonged low temperature storage, should be frequently monitored and subcultured as required. On the other hand, the woody plant stock cultures do not require any special attention when kept at 4 °C and re-grow the most vigorous shoots if stored for at least 12 weeks. This revised version was published online in August 2006 with corrections to the Cover Date.     

Survival of the mosquito predator,Notonecta unifasciata[Hemiptera: Notonectidae] embryos at low thermal gradients

Notonecta unifasciata Guerin eggs maintained at different stages of embryonic development in water at variable temperatures (2.2–25.6 °C) and for periods of 4–12 weeks revealed maximum viability (>80 %) at the highest temperature. However, optimum nondevelopmental viability was at 14.4 °C with eight-day-old embryos (>35 %). Short term (4 weeks) storage at 14.4 °C significantly increased egg viability. Survival was poor (<20 %) at the 2 lowest temperatures. Eggs held at 14.4 °C for 12 weeks and sustainingca. 50 % mortality, may be a practical procedure for biological control.      

The control of bud dormancy in potato tubers

Potato (Solanum tuberosum L.) tuber buds normally remain dormant through the growing season until several weeks after harvest. In the cultivar Majestic, this innate dormancy persisted for 9 to 12 weeks in storage at 10° C, but only 3 to 4 weeks when the tubers were stored at 2° C. At certain stages, supplying cytokinins to tubers with innately dormant buds induced sprout growth within 2 d. The growth rate was comparable to that of buds whose innate dormancy had been lost naturally. Cytokinin-treatment did not accelerate the rates of cell division and cell expansion in buds whose innate dormancy had already broken naturally. Gibberellic acid did not induce sprout growth in buds with innate dormancy. We conclude that cytokinins may well be the primary factor in the switch from innate dormancy to the non-dormant state in potato tuber buds, but probably do not control the subsequent sprout growth.Abbreviations tio ⁶ade 6-(4-hydroxy-3-methylbut-trans-2-enyl amino)purine, zeatin - tio⁶ado 6-(4-hydroxy-3-methylbut-trans-2-enyl amino)-9--D-ribofuranosyl purine, zeatin riboside     

Germplasm conservation of the tropical forest trees,Cedrela odorata L.,Guazuma crinita Mart., andJacaranda mimosaefolia D. Don., by shoot tip encapsulation in calcium-alginate and storage at 12–25°C

Germplasm conservation of the tropical forest trees,Cedrela odorata L.,Guazuma crinita Mart., andJacaranda mimosaefolia D. Don., at above-freezing temperatures following alginate-bead encapsulation was attempted. Shoot tips excised from in vitro plantlets were encapsulated in calcium-alginate beads and stored on different substrates at 12, 20, and 25 °C. Percent viability when encapsulated shoot tips were stored on substrate containing only water solidified with 1% (wt/vol) agar was 80% after 12 months at 12°C forC. odorata, 90% after 12 months at 25°C forG. crinita, and 70% after 6 months at 20°C forJ. mimosaefolia.Abbreviations BAP 6-Benzylaminopurine - KIN 6-Furfurylaminopurine     

Effect ofin vitro storage at 4°C on survival and proliferation of two apple rootstocks

One cm long shoot explants of dwarf apple rootstocks P 2 and M.9 taken from 2 year-old cultures were stored at 4°C in the dark in three media differing in concentration of growth regulators. Every 6 weeks, some explants were transferred into proliferation medium and multiplication rate was observed during three or four consecutive passages. In a second experiment, the influence of explant type (1 cm long shoot tips, 1 cm long middle part of shoots or three-shoot tufts smaller than 1 cm) and transfer time to the cold room (immediately, 10 days, or 20 days after subculture) on explant survival and proliferation were analysed.Survival of explants was influenced by composition of the storage media. On medium without 6-benzylaminopurine, 70% of P 2 and 17% of M.9 explants became necrotic during 18 weeks of storage. P 2 rootstock proliferated better in three passages after storage than did unstored controls. Storage of M.9 rootstock reduced proliferation in the first and second passages if stored in media containing 6-benzylaminopurine in comparison with unstored controls. Explants stored as tufts and transferred to the cold room directly after subculture produced more shoots during two passages than cultures stored as single shoots.     

Biology ofTrichogramma ostriniae (Hym.: trichogrammatidae) reared onOstrinia nubilalis (Lep.: pyralidae) and survey for additional hosts

Trichogramma ostriniae has been identified as a candidate for biological control ofOstrinia nubilalis. As little was known about the biology of this parasitoid when reared onO. nubilalis, we undertook experiments to quantify biological parameters important to mass-rearing and ase ofT. ostriniae. When reared continuously onO. nubilalis, femaleT. ostriniae on average lived 2.7 days and produced 24 progeny. Continuous access to honey resulted in a four-fold increase in longevity and fecundity and a significant increase in the percentage of females parasitizing eggs. Rates of fecundity and parasitism decreased with age of female. Likewise, emergence rates and percentage of female progeny decreased with age of parental female.T. ostriniae successfully parasitizedO. nubilalis eggs until the blackhead stage. Most parasitism of eggs and eclosion of adults occurred during the first half of photophase. Eggs of 13 Lepidopterans were parasitized byT. ostriniae. Eggs of the Noctuidae, Pyralidae, and Plutellidae experienced higher levels of parasitism than others tested.T. ostriniae appears to be similar to other species ofTrichogramma in several respects and does not possess any characteristics that limit its potential for mass rearing and use for augmentative biological control ofO. nubilalis.     

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24°C regimes and the 27°C/95%RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27°C/90%RH and 30°C/90%RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24°C groups and the 30°C/95%RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24°C and 90–95%RH. While mating occurred at all temperatures, none of the females laid eggs at 22°C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27°C/95%RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.     

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.     

Effects of storage at low-temperature of various heteropteran host eggs on the egg parasitoid, <Emphasis Type="Italic">Trissolcus semistriatus</Emphasis>

Various heteropteran host eggs stored under two low-temperatures were tested in the laboratory for their usability in the production of sunn pest egg parasitoid, Trissolcus semistriatus. Parasitism, adult emergence rate and development time were assesed on stored and fresh eggs of Eurygaster integriceps, Dolycoris baccarum, Graphosoma lineatum and Eurydema ornatum. Masses of fresh host eggs in microcentrifuge tubes were maintained at +6 °C and −20 °C. Every 30 days, 50 eggs of host species were exposed to parasitism by T. semistriatus. The host eggs stored at 6 °C remained viable to parasitism by T. semistriatus up to 2 months, while those of stored at −20 °C were parasitized at high rates up to 4 months, alhough succesful parasitism rates decrease with time. However, it was indicated that both fresh or stored E. ornatum eggs were not preferred to parasitism by the parasitoid. A longer development time from egg to adult was observed in stored eggs under two tested storage techniques when compared with fresh eggs.     

Cold-hardiness of Dermacentor marginatus (Acari: Ixodidae)

The cold-hardiness of Dermacentor marginatus using laboratory-reared offspring of ticks collected in Germany was characterized. Investigations of unfed stages revealed that adult ticks suffered 50% mortality at –10°C after 4–5 months, but larvae and nymphs suffered mortality within few days, whereas –15°C was lethal for all stages within a very short period. Larval hatch and moulting of engorged larvae and nymphs did not occur at 10°C. Embryonic development of eggs with larval hatch was considerably reduced by exposure of eggs to 10°C. Engorged females did not lay eggs at 10°C, the oviposition capability, however, persisted over 6 months at 10°C, 5 months at 5°C, 3 months at 0°C and 2 months at –10°C without substantial decrease of the oviposition capacity or reduction of viable eggs. These results present evidence that unfed adult ticks are the ecoepidemiologically most effective stages, which are capable to tolerate long and extremely cold winters without substantial impairment of the population density. It is also considered that engorged females interrupt their oviposition at low and subzero temperatures delaying it for months and so contribute in bypassing winter conditions. None of the stages survived supercooling indicating that D. marginatus is freeze intolerant. Mean supercooling point (SCP) ranged between –26°C in eggs and –12, 6°C in engorged females. Compared with eggs, the SCP of the other stages was significantly higher. In conclusion, the SCP is considered to have no predictive value in the context with cold-hardiness.     

Isolation and characterization ofgrandchildless-like mutants inDrosophila melanogaster

Summary Two temperature-sensitive sex-linkedgrandchildless (gs)-like mutations (gs(1)N26 andgs(1)N441) were induced by ethylmethane sulphonate inDrosophila melanogaster. They complemented each other and mapped at two different loci (1–33.8±0.7 forgs(1)N26 and 1–39.6±1.7 forgs(1)N441), which were not identical to those of any of thegs-like mutants reported in earlier work.Homozygous females of the newly isolated mutants produced eggs that were unable to form pole cells and developed into agametic adults. Competence of the embryos to form pole cells was not restored by wild-type sperm in either mutant; that is, the sterility caused by these mutations is controlled by a maternal effect.Fecundity and fertility ofgs(1)N26 females were low, and their male offspring showed a higher mortality than that of female offspring, causing an abnormal sex ratio. The frequency of agametic progeny was 93.1% and 55.8%, when the female parents were reared at 25° C and 18° C, respectively. In eggs produced by thegs(1)N26 females reared at 25° C, the migration of nuclei to the posterior pole was abnormal, and almost no pole cell formation occurred in these egg. Furthermore, half of these eggs failed to cellularize at the posterior pole. When the females were reared at 18° C, almost all of the eggs underwent complete blastoderm formation, and in half of these blastoderm embryos normal pole cells were formed.In the other mutant,gs(1)N441, the fecundity and fertility of the females were normal. The agametic frequency in the progeny was 70.8% and 18.6% when the female parents were reared at 25° C and 18° C, respectively. In the eggs laid by females reared either at 25° C or at 18° C, the migration of nuclei to the periphery and cellularization proceeded normally; nevertheless, in the majority of the embryos no pole cell formation occured at the stage when nuclei penetrated into the periplasm. When the females were reared at 18° C, some of the embryos from these females formed some round blastoderm cells with cytologically recognizable polar granules and nuclear bodies, which are attributes of pole cells. The temperature sensitive period ofgs(1)N441 was estimated to extend from stage 9 to 13 of King's stages of oogenesis.     

The life-cycle of Apatania fimbriata Pictet in the Breitenbach

The life-cycle of Apatania fimbriata (Pictet, 1843) (Trichoptera: Limnephilidae) was studied in the Breitenbach (Hesse, Federal Republic of Germany) and in the laboratory at 6 °C, 10 °C and 14 °C at 14 h day length. Embryogenesis was mainly temperature dependent in the 4 °C–18 °C range. At a constant 22 °C embryos developed to well-differentiated larvae which did not hatch. In the laboratory experiments, developmental rates increased with increasing temperature (6 °C, 10 °C and 14 °C); larvae went through a dormancy in the third and fourth larval instars; in the field this occurred between November and February. The dormancy synchronized the larval development. Laboratory studies led to the conclusion that the dormancy was not temperature dependent but endogenously determined. The emergence pattern of adults showed a clear diurnal pattern, with a maximum emergence approximately two hours after sunset. A comparison of several years emergence studies showed a decreasing number of females with increasing distance from the spring. A comparison of the dry weight of females between two traps at the stream showed a significantly higher weight from the downstream site. For males no between-site differences were observed.     

Development and reproductive biology of Laricobius nigrinus, a potential biological control agent of Adelges tsugae

Biological studies on Laricobius nigrinus Fender (Coleoptera: Derodontidae) were conducted in the laboratory to obtain basic information on this littleknown predator. Laricobius nigrinus is acandidate biological control agent of thehemlock woolly adelgid, Adelges tsugaeAnnand (Homoptera: Adelgidae), an exotic peston eastern (Tsuga canadensis (L.)Carrière) and Carolina (T.caroliniana Engelmann) hemlocks in the easternUnited States. It is univoltine andundergoes an aestival diapause. Post-aestivation activity period was 36.6 and30.8 weeks for males and females, respectively. Adult activity and oviposition are wellsynchronized with the over-wintering generationof A. tsugae. Mean lifetime fecunditywas 100.8 eggs over a mean duration of 13.2weeks oviposition period. Within thetemperature range (12–18°C) studied,development was fastest at 18°C. Meandevelopment time from egg to adult was 88.8,64.8 and 46.6 days at 12, 15 and 18°C,respectively. Laricobius nigrinus hasfour larval instars. Mean larval consumptionwas 225.9 and 252.3 A. tsugae eggs at 12and 18°C, respectively. Thesefindings provide essential data on the rate ofdevelopment and feeding capacity of L. nigrinusat temperatures typical of ambientconditions during late winter/early spring inVirginia. Its rapid development at18°C indicates that it has potential asa biological control agent of A. tsugaebecause of its synchrony with the developmentof the over-wintering generation of A. tsugaein eastern United States.     

Changes in the levels of abscisic acid and its metabolites resulting from chilling of tomato fruits

The 6,6,6-[²H]-analogues of abscisic acid (ABA), phaseic (PA) and dihydrophaseic (DPA) acids were used in GC-MS-SIM determination of free and total alkali hydrolyzable ABA, PA and DPA in the pericarp of tomato (Lycopersicon esculentum L. cv. Pik Red) fruit. Determinations were made on breaker-stage fruit stored 1, 2, 3 or 4 weeks at 2.5°C or at 10°C, and after subsequent ripening for 1 week in darkness at 20°C. Two-fold increases in levels of ABA occurred after storage at low temperatures with a slightly but significantly greater increase in ABA level occurring with 2.5°C storage. These increases in ABA levels were not associated with the appearance of damage symptoms that occurred with storage at the chilling temperature (2.5°C). Differences in ABA metabolism were found resulting from storage at the two temperatures, 2.5 or 10°C. Significantly greater DPA levels were found after 10°C storage than after 2.5°C storage (2 weeks). Levels of ABA ester-conjugates increased with 20°C ripening only after 10°C storage while free ABA levels decreased after both storage temperature conditions. Levels of DPA conjugates also increased only after 20°C ripening following 10°C storage. A longer period of storage resulted in decreases of free DPA levels after 10°C storage but increased DPA levels were found after 2.5°C storage.Abbreviations ABA abscisic acid - PA phaseic acid - DPA dihydrophaseic acid - GC-MS-SIM gas chromatography-mass spectrometry-selected ion monitoring - HPLC high pressure liquid chromatography - fw. fresh weight author for correspondence     

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.     

Summer dormancy ensures univoltinism in the predatory bug Picromerus bidens

The seasonal cycle of Picromerus bidens L. (Heteroptera: Pentatomidae) is usually considered to be univoltine with an obligatory winter egg diapause. Seasonal adaptations of the species were studied in the laboratory and in field experiments. When reared under short-day photoperiodic conditions (L12:D12 and L14:D10), all females began to lay eggs synchronously soon after their emergence. However, in the females reared under long-day conditions (L18:D6 and L20:D4) and outdoors in June–July, oviposition was significantly delayed. This delay in reproduction induced by photoperiodic conditions and then spontaneously terminated was considered to be aestivation. Egg batches laid by females in the laboratory and in the field were kept at 25 °C for two months. From 30.8 to 93.8% of batches contained eggs which hatched without cold treatment between day 14 and 60 after oviposition. The proportion of eggs hatched was 17.7 to 20.9% in the short-day regimes, while it was significantly less (5.7 to 6.0%) under long-day conditions. It is concluded that in some eggs diapause is of low intensity and that if under natural conditions the first batches had been laid at the end of June, nymphs would have hatched at least from some eggs during the same season even without cold treatment. Such untimely hatching would have resulted in the death of nymphs and adults unprepared for overwintering. A photoperiodic response which induces aestivation in the early emerging adults in June–August may prevent early oviposition and occurrence of a second generation and thus maintains univoltinism in P. bidens.