Reproductive Biology of Celatoria compressa (Diptera: Tachinidae), a Parasitoid of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

The tachinid Celatoria compressa, a parasitoid of adult Diabrotica species in North America has been studied as a candidate classical biological control agent for the western corn rootworm, Diabrotica virgifera virgifera, in Europe. Prior to its potential importation, a thorough understanding of the parasitoid's reproductive biology is essential, and is an important component in the evaluation of a species as a biological control agent. In this study it has been clarified that C. compressa belongs to a group of a few tachinid species characterised by having eggs that contain fully developed larvae which are laid directly into the host. After mating, the egg load of females increased steadily from day 1 to a maximum egg load on day 4. Thereafter eggs containing fully developed first instar larvae reached a maximum of 31 in 69 eggs. At the first day of larviposition, females laid on average only five eggs into multiple hosts, which is in contrast to the availability of 18 eggs containing fully developed first instars in the uterus per female at that time. During a mean female's larviposition period of 23 days, a total of 33 first instars were larviposited into the hosts, which is only half of the female's egg load. Lifetime fecundity of C. compressa was significantly correlated with longevity. However no relationship was found between body size and either lifetime fecundity or longevity. In this study, an inverse host density-dependent pattern of percent parasitism was shown for C. compressa under 24-h fixed-time laboratory conditions, reflecting a Holling type II response. The number of host parasitized per C. compressa female reached an upper limit of 10 hosts with an increasing host density, which can be explained by the long host handling time of C. compressa.     

Selection of entomopathogenic fungi for the control of the western corn rootworm Diabrotica virgifera virgifera

Abstract:  The western corn rootworm Diabrotica virgifera virgifera Le Conte (Col., Chrysomelidae), a serious pest of maize, has been recently introduced into Europe. Several approaches for its control are presently under investigation including microbial agents. During a field survey in Hungary in 2005, naturally occurring entomopathogenic fungi were found to attack this pest. These novel isolates together with standard isolates were tested for virulence against D. v. virgifera larvae and adults. Twenty strains of Metarhizium anisopliae , Beauveria bassiana and Beauveria brongniartii were used in bioassays in the laboratory. Larvae and adults were dipped into a spore suspension with a concentration of 1 × 10⁷ conidia (con.)/ml. They were kept for 14 days at 22°C (±2°C) and 70% relative humidity. The number of infected larvae and adults were counted and infection rates were calculated. Adults were significantly more susceptible to entomopathogenic fungi than larvae. The most virulent isolate infected about 47% of larvae ( M. anisopliae Ma2277), whereas the infection rate in adults was up to 97% ( M. anisopliae Ma2275). Isolates of M. anisopliae caused significantly higher mortalities than isolates of B. brongniartii and B. bassiana . Most of the adult beetles were killed within 12 days. Isolates from D. v. virgifera were more virulent than those from other hosts.     

Population dynamics of a Western corn rootworm (Coleoptera: Chrysomelidae) variant in east central Illinois commercial maize and soybean fields

Three on-farm sites in Iroquois County, IL, each containing an adjacent 16.2-ha commercial production maize, Zea mays L., and soybean, Glycine max (L.) Merr., field, were monitored for western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), adults from June through September 1999-2001. Mean captures of D. v. virgifera adults as measured with Pherocon AM yellow sticky traps were significantly greater in maize than in soybean. Overall mean numbers of D. v. virgifera adults captured with vial traps were significantly greater in soybean than in maize. Emergence cage data revealed that after 50% emergence of D. v. virgifera adults occurred, peak captures of D. v. virgifera adults occurred in maize as measured with vial and Pherocon AM traps. After maize reached the R2 (blister stage, 10-14 d after silking) stage of development and 90% emergence of D. v. virgifera adults had occurred, peak captures of D. v. virgifera adults were observed in soybean by using vial and Pherocon AM traps. Also, after maize reached the R2 stage of development, numbers of females significantly increased in soybean and decreased in maize. Captures of female D. v. virgifera adults frequently exceeded published economic thresholds in soybean, regardless of trap type used. Estimated survival of variant D. v. virgifera (egg to adult) in these commercial rotated maize fields was 10.7 and 9.4% from 1999 to 2000 and from 2000 to 2001, respectively. This compares with nonvariant D. v. virgifera survival estimates in continuous maize production systems in Iowa of 6.7 and 11% from 1983 to 1984 and from 1984 to 1985, respectively.     

Screening of entomopathogenic nematodes for virulence against the invasive western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) in Europe

Entomopathogenic nematode species available in Europe were screened for their efficacy against both the root-feeding larvae and silk-feeding adults of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Laboratory screening tests were aimed at the selection of candidate biological control agents for the management of this invasive alien pest in Europe. Steinernema glaseri, S. arenarium, S. abassi, S. bicornutum, S. feltiae, S. kraussei, S. carpocapsae and Heterorhabditis bacteriophora were studied to determine their virulence against third instar larvae and adults of D. v. virgifera in small-volume arenas (using nematode concentrations of 0.5, 0.8, 7.9 and 15.9 infective juveniles cm-2). All nematode species were able to invade and propagate in D. v. virgifera larvae, but adults were rarely infected. At concentrations of 7.9 and 15.9 cm-2, S. glaseri, S. arenarium, S. abassi and H. bacteriophora caused the highest larval mortality of up to 77%. Steinernema bicornutum, S. abassi, S. carpocapsae and H. bacteriophora appeared to have a high propagation level, producing 5970+/-779, 5595+/-811, 5341+/-1177 and 4039+/-1025 infective juveniles per larva, respectively. Steinernema glaseri, S. arenarium, S. feltiae, S. kraussei and H. bacteriophora were further screened at a concentration of 16.7 nematodes cm-2 against third instar larvae in medium-volume arenas (sand-filled trays with maize plants). Heterorhabditis bacteriophora, S. arenarium and S. feltiae caused the highest larval mortality with 77+/-16.6%, 67+/-3.5%, and 57+/-17.1%, respectively. In a next step, criteria for rating the entomopathogenic nematode species were applied based on results obtained for virulence and propagation, and for current production costs and availability in Europe. These criteria were then rated to determine the potential of the nematodes for further field testing. Results showed the highest potential in H. bacteriophora, followed by S. arenarium and S. feltiae, for further testing as candidate biological control agents.     

Genes, gene flow and adaptation of Diabrotica virgifera virgifera

1  Diabrotica virgifera virgifera has emerged as a major pest of cultivated maize, due to a combination of its high capacity to inflict economic damage, adaptability to pest management techniques and invasiveness.
2 This review presents a survey of the current state of knowledge about the genetics of D.   v.   virgifera . In addition, the tools and resources currently available to Diabrotica geneticists are identified, as are areas where knowledge is lacking and research should be prioritized.
3 A substantial amount of information has been published concerning the molecular phylogenetic relationships of D.   v.   virgifera to other chrysomelids.
4 There is a growing literature focused on the population genetics and evolution of the species. Several adaptations to anthropogenic selection pressure have been studied, with resistance to synthetic insecticides providing some particularly well-characterized examples.
5 A notable deficiency is a lack of studies directed toward the formal genetics of D.   v.   virgifera .     

Relationship between phenotypic traits and selected fitness components of Diabrotica virgifera virgifera

Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) is one of the most important and best-studied maize pests, yet little information is available regarding the basic relationships among its phenotypic traits, particularly those that reflect the overall fitness of this successful invader in Europe and North America. Such information is critical for studies on the invasiveness, behavioural ecology, and management of this pest. Phenotypic traits that change over the lifetime of the beetle were investigated (e.g., fresh body weight) as they can indicate changes in adult physiology or fitness of D. v. virgifera . Phenotypic traits that remain stable over the beetle's lifetime were also investigated (e.g., pronotum width, head capsule width, hind tibia length), as they most likely allow detection of genetic differences between populations. Furthermore, phenotypic traits were investigated that may best predict fecundity (e.g., fresh body weight, elytra width) and life span (e.g., elytra length), as these two factors influence the population growth of this highly invasive species. Finally, regression equations are provided for the age-specific oviposition and survival of the long-living D. v. virgifera adults, which may allow researchers to reduce the duration of their bioassays without losing information.     

The contribution of prehatch and posthatch development to protandry in the chrysomelid Diabrotica virgifera virgifera

Laboratory tests with eggs of Diabrotica virgifera virgifera LeConte showed that during a 10-day hatching period, hatch of male eggs predominated on the first and second days, eggs of mixed sex, with ca. 1:1 ratio, hatched on the third and fourth days, and eggs hatching from the fifth to the tenth days were nearly all female. Overall, female eggs hatched a mean of 2.9 days later than male eggs. Not only did female eggs hatch later, but the time for posthatch development to the adult stage was 1.8 days longer for females. The later egg hatch and longer posthatch development for females resulted in female adults emerging a mean of 4.7 days later than male adults. Total adult emergence lasted 14 days; of this, males predominated during the first 5 days, and females predominated during the last 9 days. Males of D. v. virgifera appear to have evolved protandry (the tendency for males to emerge before females) by developing both a postdiapause embryonic stage and a combined larval and pupal stage of shorter duration.

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Résumé L'observation, au laboratoire, pendant une période d'éclosion de dix jours, des oeufs de D. v. virgifera LeConte, a montré que les oeufs mâles prédominent les deux premiers jours d'éclosion, que les oeufs des deux sexes, avec des fréquences 0,5/0,5, ont éclos les troisième et quatrième jours, et que les oeufs éclos du cinquième au dixième jour étaient presque tous femelles. Globalement, les oeufs femelles ont éclos en moyenne 2,9 jours plus tard que les oeufs mâles. De plus, la durée du développement post-embryonnaire des femelles a demandé 1,8 jour en plus. Une éclosion plus tardive et un développement post-embryonnaire plus long ont entrainé une émergence des femelles en moyenne 4,7 jours après les mâles. La période d'émergence des adultes s'est étalée sur 14 jours; les mâles ayant dominé pendant les 5 premiers jours et les femelles pendant les 9 derniers. Les mâles de D. v. virgifera semblent avoir évolué vers la protandrie en acquerant, tant une diapause post-embryonnaire que des stades de développements larvaire et nymphal plus brefs.

     

Response of larvae of invasive maize pest Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) to carbon/nitrogen ratio and phytosterol content of European maize varieties

We studied the performance of larvae of Diabrotica virgifera virgifera LeConte (Chrysomelidae, Galerucinae) on 17 different maize, Zea mays L., varieties from six European countries. Food conversion efficiency studies were performed using a newly established method. The growth of D. v. virgifera (western corn rootworm) larvae and the amount of ingested food was measured and the food conversion efficiency was calculated. In addition, we analyzed the carbon/nitrogen ratio and the phytosterol content of the different varieties. Significant differences between the maize varieties with regard to larval weight gain, amount of ingested food, and food conversion efficiency were encountered. The efficiency of D. v. virgifera in converting root biomass into insect biomass was positively related to the amount of nitrogen in the plant tissue. Furthermore the root phytosterol content influenced the larval weight gain and the amount of ingested food. It was possible to group the varieties into suitable and unsuitable cultivars with regard to D. v. virgifera larval performance on the basis of the phytosterol content. Our results provide the first evidence of the high variability among European maize varieties with respect to D. v. virgifera nutrition. The use of less suitable maize varieties is discussed with respect to integrated pest management strategies.     

Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) larval feeding behavior on transgenic maize (MON 863) and its isoline

Diabrotica species (Coleoptera: Chrysomelidae) larval behavior studies have posed a challenge to researchers because of the subterranean life cycle of this pest. To fully understand how the western corn rootworm, Diabrotica virgifera virgifera LeConte, injures the maize, Zea mays L., root system, its behavior must be studied. For example, larvae that can detect an area of the root that has a lower amount of toxin, whether from an insecticide or a transgenic maize plant, have an increased chance of survival. This study assessed D. v. virgifera larval feeding behavior on rootworm-susceptible maize and maize containing a biotechnology-derived trait (MON 863) with resistance to D. v. virgifera first instar feeding. Maize plants were grown in a medium that allowed for direct observation and measurements during feeding of larval stadia. Neonates were placed on maize seedlings, and data were taken at 3, 6, 9, and 12 d postinfestation on resistant and susceptible maize. On rootworm-susceptible maize, neonate larvae aggregated at the root tips and began actively feeding, and then they moved to older root tissue. Conversely, some larvae that ingested Cry 3Bb1 from the resistant maize exhibited no movement. Other larvae on the resistant maize moved continuously, sampling root hairs or root tissue but not actively feeding. The continuously moving larvae had visibly empty guts, suggesting possible nonpreference for the resistant root. This study contributes to our understanding of D. v. virgifera larval behavior and provides insight into questions surrounding the potential evolution of behavioral and biochemical resistance to Cry3Bb1.     

Spatial clustering of Diabrotica virgifera virgifera and Agriotes ustulatus in small-scale maize fields without topographic relief drift

The soil‐living larvae of Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) and Agriotes ustulatus Schaller (Coleoptera: Elateridae) can cause economic damage to maize roots, Zea mays L. (Poaceae). This study investigated the spatial clustering of both pests in four small‐scale maize fields in southern Hungary, where clustering had been observed but not expected due to the lack of topographic relief drifts and soil structuring. Between 2000 and 2002, numbers of D. v. virgifera larvae and adults and of A. ustulatus larvae were determined at four randomly chosen georeferenced maize plants in each of 24 plots per field. Soil moisture, soil bulk density, and vegetational characteristics were assessed. Moran's I test for spatial autocorrelations, semivariogram analyses, and interpolated mapping revealed that D. v. virgifera larvae and adults were spatially clustered in 67 and 50% of cases, respectively. Larvae of A. ustulatus were clustered in 75% of cases. Diabrotica virgifera virgifera larval distributions were mainly determined by increasing weed density (negative correlation), in particular with high densities of Cirsium arvense (L.) (Asteraceae), as well as by increasing soil moisture (negative correlation). Adult distributions of D. v. virgifera were mainly determined by the density distribution of flowering maize. They were moreover correlated with larval distribution and with the adult distribution of the previous year. The density distributions of male adults differed from those of females. Female density was additionally correlated with higher soil moisture and Poaceae density, e.g., with Sorghum halepense (L.) Pers. No relation was found between the larvae of A. ustulatus and D. v. virgifera. Agriotes ustulatus larval distributions were mainly determined by vegetational cover (correlation with less cover). Conclusively, male and female D. v. virgifera adults, larvae of D. v. virgifera, and larvae of A. ustulatus will display different spatial clustering even within ostensibly homogeneous habitats of flat small‐scale maize fields.     

Reproductive biology of the microtype tachinid fly Zenillia dolosa (Meigen) (Diptera: Tachinidae)

Reproductive biology including mating, adult longevity, fecundity and development of the tachinid fly Zenillia dolosa was investigated for optimizing rearing procedures using Mythimna separata as a host in the laboratory. Females lay microtype eggs containing a first instar larva on food plants of the host and then the eggs must be ingested by the host for parasitization. Mating success was 58.5% with mating duration of 80.7 min. Mating was most successful when day 0–1 females were kept with day 2–4 male flies. Female body size was positively correlated with its fecundity but not with longevity. However, females that survived longer produced more eggs during their lifetime. Parasitoids successfully developed in 4th to 6th instar host larvae. Host instars at the time of parasitoid egg ingestion significantly influenced development time of the immature parasitoid, but did not affect body size of the emerging parasitoid. We suggest that pairing newly emerged females with day 2–4 males should result in higher mating success and using the last instar hosts for parasitization should minimize development time of the parasitoid for rearing.     

Mobility of mass-reared diapaused and nondiapaused Cydia pomonella (Lepidoptera: Tortricidae): effect of mating status and treatment with gamma radiation

Mass-reared insects may differ in their behavioral traits depending on whether they have undergone diapause. We studied the mobility of mass-reared diapaused and nondiapaused Cydia pomonella (L.) with a focus on understanding the effect of mating status and treatment with gamma radiation as these insects are destined for use in an areawide program that uses the sterile insect technique (SIT). Actograph-measured mobility was assessed one gender at a time for 4 h during which the photoperiod transitioned from day to night. We tested 20-30 individuals per treatment. For experiments on the effect of mating status, we used 24-48-h-old adults (diapause [D]-virgin, D-mated, standard [N]-virgin, and N-mated), which is the typical age class that is released in the SIT program. Diapaused females were significantly more mobile than females reared through standard production, whereas no differences were detected in male mobility because of rearing strategy. Mated females were significantly more mobile than virgin females, whereas no difference in mobility because of mating status was detected for males. Mated females were significantly more mobile than mated males. In contrast, virgin females were significantly less mobile than virgin males. For experiments on the effect of treatment with gamma radiation, adults from all rearing strategies and treatments (D-0Gy, D-100Gy, D-250Gy, N-0Gy, N-100Gy, and N-250Gy), were tested simultaneously. Adult males were tested at two different constant temperatures (25 and 20 degrees C), whereas adult females were tested only at 25 degrees C. For standard-reared adults, we found a significant linear decrease in mobility as the radiation dose increased from 0 to 250 Gy. In contrast, the relationship between mobility and dose of radiation was quadratic for diapaused males and absent for diapaused females.     

The effects of a winter cover crop on Diabrotica virgifera (Coleoptera: Chrysomelidae) populations and beneficial arthropod communities in no-till maize

The effects of an autumn-planted, spring-killed, grass cover crop (Elymus trachycaulus [Link] Gould ex Shinners) on populations of Diabrotica virgifera virgifera LeConte and its predator community were evaluated in South Dakota maize fields over two seasons. Abundance and size of D. virgifera larvae and adults and sex ratio of adults were measured in maize produced under two treatments (i.e., a winter cover crop or bare soil), as were maize root damage and the abundance and diversity of the predator communities collected on the soil surface and in the soil column. First and second instars and adults of D. virgifera were similarly abundant in the two treatments, but third instars were significantly fewer in maize planted after a winter cover crop. Larvae developed at different rates in the two treatments, and second instars were significantly smaller (head capsule width and body length) in the maize planted after a cover crop. First and third instars and adults were of similar size in the two treatments, and adult sex ratios were also similar. Although initially similar, predator populations increased steadily in the cover-cropped maize, which led to a significantly greater predator population by the time D. virgifera pupated. There was significantly less root damage in the cover-cropped maize. Predator communities were similarly diverse in both treatments. Predator abundance per plot was significantly and negatively correlated with the abundance of third instars per plot. Clearly, winter cover crops reduce D. virgifera performance and their damage to the crop, and we suspect that this reduction is caused by both environmental effects of the treatment on D. virgifera size and development, and of increased predation on the third instars of the pest. Additional data on the impact of cover crops on actual predation levels, grain yield and quality, and farmer profitability, and correlations among pest performance, crop characteristics, and predator populations and behaviors are key components of this system that remain to be addressed.     

Adult movements of newly introduced alien Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) from non-host habitats

Mark-release-recapture experiments were undertaken in order to investigate the movement of adult Diabrotica virgifera virgifera LeConte from accidental introduction points towards suitable habitats, such as its host plant, Zea mays L. In Hungary in 2003 and 2004, nine mark-release-recapture experiments were carried out in a grass steppe area and lucerne field, in which two small maize fields (10x10 m) had been planted 300 m distant from the central release point. After each release of 5500 to 6000 marked D. v. virgifera, beetle recaptures were recorded three times using non-baited yellow sticky traps placed on 30, 105, 205 and 305 m radii around the release point. In seven out of 15 recapture periods (47%), beetle populations showed no directional movements, and their movements towards any particular habitat cannot be predicted. During five recapture periods (33%), beetle populations showed a uni-directional movement, and in three cases (20%) a bi-directional movement was observed. In 10 out of 15 recapture periods (67%), the released populations moved in a direction that was comparable with the mean wind direction during these periods; thus, beetle movements were slightly correlated with wind direction. On average over sites and years, beetles were not preferentially moving towards the two small maize fields (located 300 m from the release point) compared to other directions. However, beetles moved significantly more frequently in the direction of naturally-occurring maize fields within a radius of 1500 m than towards other habitats. Beetles stayed more frequently within flowering lucerne fields out to a radius of 300 and 600 m than in non-flowering lucerne or other habitats. On average, 2.8% (SD 3.2) of all recaptured beetles arrived in one of the two small maize fields located 300 m from their release point indicating that there is a high risk of a founder population establishing. Habitat management cannot be suggested as a means of preventing the beetle's initial dispersal because movement was usually non-directional, and alternative food plants were used prior to reaching maize.     

Life history of Spalangia gemina Boucek (Hymenoptera: Pteromalidae), a fast-breeding microhymenopteran pupal parasitoid of muscoid flies

Laboratory studies at 25.5 degrees C and 70-75% r.h. demonstrated that the average daily survival rate for females of the parasitoid Spalangia gemina Boucek (Hymenoptera: Pteromalidae) was 0.907 over a 20-day period, with 50% mortality in 17.3 days. Mean immature developmental time of S.gemina was 22 days and the population growth rate was c. 40-fold per generation. The females successfully parasitized 1-, 2- and 3-day-old pupae of Musca domestica L. and parasitism of 98-100% was obtained at parasitoid to host ratios of 1:0.5-2.5. Parasitism of 81-87% was obtained at parasitoid to host ratios of 1:10. The male to female sex ratio was 1:1.59. S.gemina appears to have advantages over other Spalangia spp., which have immature development times of 28-32 days under comparable conditions, for the biological control of Muscidae.     

A mass rearing method for the linyphiid spider species Erigone atra (Blackwall) (Araneae: Linyphiidae)

Abstract:  A mass rearing method for Erigone atra (Blackwall) (Araneae: Linyphiidae) allowing continuous laboratory rearing is described. Twenty 1–2-day old spiderlings were kept together in plastic boxes, which were filled with soil containing a culture of the Collembola species, Lepidocyrtus lanuginosus (Gmelin) (Entomobryidae), and serving the spiders as a continuous available prey source. Once per week vestigial-wing fruit flies of Drosophila melanogaster Meigen (Diptera: Drosophilidae) were provided as additional prey. In addition, the rearing boxes were filled with wood-wool serving spiders as points of contact for their webs. After 3–5 weeks most of the spiderlings developed to adults, which were separated individually into glass tubes filled with soil and Collembola until all of them became adult. To produce a new generation of spiders 20–40 adult/subadult spiders originating from different mass rearing boxes were brought together and kept and fed in the same way as the spiderlings. Within a few days females started to produce eggsacs. The eggsacs were transferred into glass tubes filled with a layer of moist plaster of Paris until the spiderlings hatched, which were then bred as described above. Erigone atra was bred over 12 generations within a period of 2 years. The mean rearing success (from 1 to 2-day-old spiderlings to adults) was 59.3%. Decreasing rearing success, decrease of fecundity or decrease of adult spider size were not observed. Advantages and use of the mass rearing method are discussed in relation to rearing methods for other spiders.     

Genome scan of Diabrotica virgifera virgifera for genetic variation associated with crop rotation tolerance

Abstract:  Crop rotation has been a valuable technique for control of Diabrotica virgifera virgifera for almost a century. However, during the last two decades, crop rotation has ceased to be effective in an expanding area of the US corn belt. This failure appears to be due to a change in the insect's oviposition behaviour, which, in all probability, has an underlying genetic basis. A preliminary genome scan using 253 amplified fragment-length polymorphism (AFLP) markers sought to identify genetic variation associated with the circumvention of crop rotation. Samples of D. v. virgifera from east-central Illinois, where crop rotation is ineffective, were compared with samples from Iowa at locations that the behavioural variant has yet to reach. A single AFLP marker showed signs of having been influenced by selection for the circumvention of crop rotation. However, this marker was not diagnostic. The lack of markers strongly associated with the trait may be due to an insufficient density of marker coverage throughout the genome. A weak but significant general heterogeneity was observed between the Illinois and Iowa samples at microsatellite loci and AFLP markers. This has not been detected in previous population genetic studies of D. v. virgifera and may indicate a reduction in gene flow between variant and wild-type beetles.     

Delayed mating reduces reproductive output of female European grapevine moth,Lobesia botrana (Lepidoptera: Tortricidae)

Virgin females of Lobesia botrana Denis & Schiffermüller were mated at ages of 1, 3, 5, 8, 12 and 16 days and the effect of mating delay on reproductive output assessed. Delayed mating did not affect female mating success but fertilization was reduced in 16-day-old females. Increased mating delays substantially affected daily oviposition pattern and resulted in a significant reduction of both fecundity and fertility, so that mean number of viable eggs laid decreased from 150 to 22 in 1- and 16-day-old mated females, respectively. Heavier females were more constrained than lighter ones by mating delays and female reproductive efficiency (no. viable eggs/female body weight) was also significantly reduced. Female longevity significantly increased and oviposition period gradually declined with mating delay. The number of viable eggs was positively correlated with both female weight and oviposition period; female longevity and female weight were also significantly correlated. However, the significance of these correlations declined with increased mating delay. Results overall indicated that mating delay drastically reduces female L. botrana reproductive output. The implications of delayed mating of females are discussed from an ecological perspective in relation to L. botrana control using mating disruption.     

Biology and thermal requirements of Trichogramma atopovirilia Oatman & Platner (Hymenoptera: Trichogrammatidae) parasitizing eggs of Diaphania hyalinata L. (Lepidoptera: Pyralidae)

The development and parasitism of Diaphania hyalinata L. eggs by Trichogramma atopovirilia Oatman & Platner and its thermal requirements were studied at the temperatures of 18, 21, 24, 27, 30 and 33 degrees C. Thirty eggs of D. hyalinata were exposed to three females of T. atopovirilia for 5h at 25 degrees C and incubated at the different temperatures. The developmental time from egg exposure to adult, parasitism viability, number of adults per parasitized host egg and progeny sex ratio were monitored. The developmental time from egg to adult emergence of the parasitoid exhibited inverse relationship to the temperature, lasting 24.12 days at 18 degrees C and 7.36 days at 33 degrees C. Parasitism viability at 24, 27 and 30 degrees C was higher than 90%. The ratio of T. atapovirilia adult produced per egg and its sex ratio were not affected when using D. hialynata as host. The lowest threshold temperature (Tb) and estimated degree-days over Tb required by T. atopovirilia to develop on eggs of D. hyalinata was 11.99 degrees C and 130.42 masculine C, respectively. Considering the temperature regimes of two areas where cucurbitaces are cultivated in Bahia State (Rio Real and Inhambupe County) it was estimated that T. atopovirilia can achieve more than 32 generation per year. The results suggest that T. atopovirilia has potential to control D. hyalinata eggs with better chance of success under temperature regimes ranging from 24 to 27 degrees C that meets the suitable field conditions for cropping cucurbitaces.     

The biology of Diadromus collaris (Hymenoptera: Ichneumonidae), a pupal parasitoid of Plutella xylostella (Lepidoptera: Plutellidae), and its interactions with Oomyzus sokolowskii (Hymenoptera: Eulophidae)

The ichneumonid Diadromus collaris (Gravenhorst) has been recorded in many parts of the world as an important parasitoid of the diamondback moth, Plutella xylostella (Linnaeus), a serious pest of brassica vegetable crops worldwide. Some aspects of its biology and its interactions with Oomyzus sokolowskii (Kurdjumov), another major parasitoid of the same pest, were studied in the laboratory. At 25 degrees C, female wasps did not have mature eggs in their ovaries until about 12 h after emergence. Both males and females mated successfully 24-48 h after emergence, and females started to oviposit one to two days after emergence. Unmated females produced male progeny only; mated females produced progeny of both sexes. The development rate of the parasitoid increased linearly with temperature from 15 to 30 degrees C, with an estimated low temperature threshold of 7.4 degrees C and a thermal constant of 225.1 day-degrees for development from egg to adulthood. Rates of survival from larva to adulthood were about 90% between 20 and 28 degrees C and decreased as temperature decreased or increased. No immatures survived to adulthood at 35 degrees C. When provided with honey solution, the females lived on average 8.3, 11.5 and 7.0 days, and parasitized 26, 44 and 46 host pupae at 20, 25 and 30 degrees C, respectively. Female wasps could be stored at 15 degrees C for up to four weeks without detrimental effects on reproduction. Females of D. collaris attacked host pupae already parasitized by O. sokolowskii, inserting their ovipositor into the hosts at a similar frequency as into unparasitized host pupae, but they did not lay eggs inside the hosts.