Percentage Egg Hatch Research Articles

Pre-adult mortality in the blowfly Lucilia sericata.

Populations of the blowfly, Lucilia sericata (Meigen) (Diptera: Calliphoridae), have a considerable potential for rapid increase; the lifetime reproductive output of each adult female has been estimated to be between 130 and 172 eggs. Nevertheless, in the field, absolute population densities of this species are relatively low. To account for this difference, the levels of mortality affecting the eggs, feeding and wandering larvae and pupae of L. sericata were assessed in the field and laboratory. Percentage egg hatch was dependent on relative humidity with no egg eclosion at humidities below 50%; there was no significant effect of temperature on egg hatch. On infested sheep, the mean mortality of feeding larvae was 53%, but this ranged widely from 0% to 96%. There was no effect of atmospheric temperature or humidity on the mortality of feeding larvae in vivo. In the laboratory, only 10% of wandering larvae pupariated at 10 degrees C. At above 20 degrees C pupariation was consistently almost 100%. Percentage emergence increased from 0% at 10 degrees C to about 80% between 20 and 30 degrees C. The upper lethal temperature for pupae was approached at 35 degrees C. Analysis of the predation of pupae in the field revealed a weak, but significant curvilinear relationship between temperature and proportionate mortality and a median mortality of 0.49% per 24 h exposure (interquartile range = 5.2%). There was no evidence of density dependence in pupal predation. Overall, it is estimated that pre-adult mortality accounts for losses of approximately 97% of each generation, but this figure is subject to considerable variation depending on factors such as climate, time of year and host susceptibility.

Temperature and relative humidity effects on egg and nymphal development of Aceria tulipae (K.) (Acari: Eriophyidae) on garlic leaves (Allium sativum L.)

Summary Aceria tulipae (K.) is responsible for important crop losses of garlic in all production areas around the world. However, very little is known about its development in relation to temperature and relative humidity (r.h). Laboratory rearings from egg to adult stage were done on pieces of the apical part of young garlic leaves. These leaf pieces were placed in aluminium dishes floating on water or put on a solid hygroscopic salt in closed plastic trays. Rearing done in dark incubators at constant temperatures (10°C to 45°C) and with different r.h (25% to 75%) at 15°C and 25°C showed that: i) the shortest development time occurs at about 25°C; ii) the upper lethal temperature and the development threshold for the eggs are respectively estimated about 45°C and 6°C; iii) a r.h close to 100% is required for a high percentage of egg hatching, but water condensation on leaves is harmful. Host transpiration has an important regulatory effect on humidity conditions favouring mite survival.

Biological control of Bactocera oleae (Diptera: Tephritidae) using a Greek Bacillus thuringiensis isolate.

Bacillus thuringiensis, isolate 114A, was used in toxicity experiments against the wild population ofthe olive pest Bactroceria oleae (Gmelin). In laboratory experiments, spores and crystals of the B.t. were delivered to the insects with the food. Longevity, oviposition period, number of eggs produced, and percent hatch were recorded. Olive fruits from the oviposition test were dipped into a suspension containing spores and crystals of B. thuringiensis 114A after the eggs were deposited. In field experiments, four to six sprayings per year of B.t. 114A isolate were applied for three successive years. It was found that, in addition to the longevity of B. oleae, the oviposition period, number of eggs and percent egg hatch decreased. Also, the percentage of pupation and emergence was reduced when olive fruits with eggs in their mesocarp were dipped in the solution of spores and crystals. Field applications with the toxins of 114A isolate of B. thuringiensis have resulted in significant protection of the olive production.

Serial Selection for Resistance to a Wild-Type and to a Genetically Modified Nucleopolyhedrovirus in Trichoplusia ni

Abstract In previous work, cabbage loopers ( Trichoplusia ni ) evolved 22-fold resistance to the single nucleocapsid nucleopolyhedrovirus of T. ni (TnSNPV) after 26 generations of selection with the virus. The goal of the present study was to determine if T. ni could evolve resistance to the recombinant Autographa californica multiple nucleocapsid nucleopolyhedrovirus (AcMNPV-AaIT) that expresses an insect specific neurotoxin and to determine if it was influenced by prior development of resistance to TnSNPV. To answer these questions, the T. ni line that had been exposed to TnSNPV was divided into two sublines at generation 27. One of them was serially selected for resistance to AcMNPV-AaIT (subline TnSNPV/AcMNPV-AaIT), while the other one was mock infected with distilled water (subline TnSNPV/H 2 O). The same was done with the line that was used as a control from generations 1 to 26 (subline H 2 O/AcMNPV-AaIT and subline H 2 O/H 2 O). After 17 generations of selection with AcMNPV-AaIT, T. ni that had not been previously exposed to TnSNPV evolved only twofold resistance to AcMNPV-AaIT. However, those that had been selected with TnSNPV evolved fourfold resistance to AcMNPV-AaIT. Exposure to AcMNPV-AaIT conferred cross-resistance to TnSNPV in only one subline, subline H 2 O/AcMNPV-AaIT. Resistance to AcMNPV-AaIT did not affect the developmental time, pupal weight, egg production, or percentage of egg hatch of T. ni.

Temperature tolerance of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae) in tropical and temperate regions of Asia.

Temperature tolerance was investigated in nine populations of Plutella xylostella Linnaeus from tropical and temperate regions of Asia. At all rearing temperatures between 15 and 35 degrees C, no clear differences were observed in female egg production or larval development between tropical and temperate populations. Thus, tropical populations did not show a high-temperature tolerance superior to that of the temperate populations. In all populations, the net reproductive rate (number of new females born per female) largely depended on the number of eggs laid per female, and egg production significantly decreased with increasing temperature (P < 0.001). Larval developmental rate also showed a significant positive correlation with temperature (P < 0.001). Per cent hatch of eggs and larval survival did not show a significant correlation with temperature: hatching was constant between 15 and 32.5 degrees C, but considerably lower at 35 degrees C. Larval survival was similar between 15 and 30 degrees C, appreciably lower at 32.5 degrees C and declined to 0% at 35 degrees C. Based on these results, environmental conditions under which P. xylostella can maintain a high population density throughout the year in tropical and subtropical regions are discussed.

Oviposition and Maintenance of &lt;I&gt;Forcipomyia (Lasiohelea) townsvillensis&lt;/I&gt; (Diptera: Ceratopogonidae) in the Laboratory

Fecundity, oogenesis, oviposition, and percentage egg hatch were quantified for the blood-feeding midge Forcipomyia (Lasiohelea) townsvillensis (Taylor). Data are similar to that reported for other species of blood-feeding Forcipomyia. Eggs rarely developed from a partial blood meal but invariably developed after a single, complete blood meal. Results suggest that this species is anautogenous. Oviposition media were investigated and a successful medium and holding chamber type identified. Longevity of adults in the laboratory was studied and indicates the possibility for >1 gonotrophic cycle to occur. Adult survival at different relative humidities showed midges can survive 35-98% RH. Rearing of larvae in the laboratory and culture media are discussed. The data supplied in this paper provide the basis for the laboratory culture of F. (L.) townsvillensis.

Oviposition and Maintenance of Forcipomyia (Lasiohelea) townsvillensis (Diptera: Ceratopogonidae) in the Laboratory

Fecundity, oogenesis, oviposition, and percentage egg hatch were quantified for the blood-feeding midge Forcipomyia (Lasiohelea) townsvillensis (Taylor). Data are similar to that reported for other species of blood-feeding Forcipomyia. Eggs rarely developed from a partial blood meal but invariably developed after a single, complete blood meal. Results suggest that this species is anautogenous. Oviposition media were investigated and a successful medium and holding chamber type identified. Longevity of adults in the laboratory was studied and indicates the possibility for >1 gonotrophic cycle to occur. Adult survival at different relative humidities showed midges can survive 35-98% RH. Rearing of larvae in the laboratory and culture media are discussed. The data supplied in this paper provide the basis for the laboratory culture of F. (L.) townsvillensis.

Effects of Soybean Mosaic Virus on the Facultative Phytophagous PredatorOrius insidiosus(Heteroptera: Anthocoridae)

Orius insidiosus (Say) is an important predator in soybeans, feeding on thrips, aphids, and other small arthropods. This predator also feeds on plant tissues, and can be affected by the plant’s physiological status, which is altered by age of the leaves or diseases such as soybean mosaic virus. This study examined the effects of soybean mosaic virus on longevity and fecundity of O. insidiosus, as a result of feeding on soybean leaves of different ages infected with a mild or a severe strain of the virus. Females provided with prey on uninfected plants and on plants infected with a mild virus strain lived longer than females on plants infected with a severe strain. When caged on leaves without prey, females lived longer on older and younger leaves than on middle-aged leaves. Fecundity and percentage of egg hatch did not differ significantly between leaf ages and virus strains. Leaf hair density appeared to have the greatest effect on longevity and fecundity; when the leaf hairs were sparse enough for O. insidiosus to reach the leaf’s surface readily, other chemical factors, such as amino acid and starch levels, may have influenced the longevity and fecundity of O. insidiosus. This study shows that some plant stresses might negatively effect yield both through direct reduction in plant health and indirectly when the plant stresses reduce the predator population. Because many heteropteran generalist predators are also facultatively phytophagous, we need to consider the dual impact of plant stresses on crop yields and on these important biological control agents.

Efficacy of coumaphos applied as a dip for control of an organophosphorus-resistant strain of Boophilus microplus (Acari: Ixodidae) on cattle.

The efficacy of coumaphos, an organophosphorus acaricide, was tested on a strain of Boophilus microplus (Canestrini) that was 9.5 times more resistant to the chemical than a susceptible strain. Cattle infested with larval, nymphal, and adult ticks were dipped into a vat charged at concentrations of 0.031, 0.083, 0.160, and 0.279% (AI). Assessment of efficacy was based on surviving tick numbers, female weight, egg mass weight, egg hatchability, and index of reproduction. At 0.031% (AI), the level of control was lower than the other coumaphos treatments, and the weight, fecundity, and fertility of surviving females was similar to untreated females, indicating only minimal adverse effects on the ticks. At 0.160 and 0.279% (AI), no differences in control, female weight, egg mass weight, or percentage egg hatch were observed, but effects were greater than that of untreated ticks or ticks treated at 0.031% (AI). At 0.083% (AI), most biological parameters were intermediate, but there was no difference in control compared with the 2 higher concentrations. Thus, even with the increase in concentration of more than 3 times between treatments of 0.083 and 0.279% (AI), there was no substantial increase in control. The residual efficacy of all 4 treatments showed that none provided complete protection against larval reinfestation for even 1 wk after treatment. Therefore, the presence of organophosphorus-resistant ticks at U.S. ports-of-entry could jeopardize the success of the Boophilus eradication program.

Factor from Swamp Water Induces Hatching in Eggs ofAnopheles diluvialis(Diptera: Culicidae) Mosquitoes

Anopheles quadrimaculatus Say, An. smaragdinus Reinert, and An. diluvialis Reinert mosquitoes are recently described sibling species that occur in northern Florida where the adults are sympatric but larvae develop in different aquatic habitats. The hatching dynamics of these species showed that An. diluvialis utilizes a hatching stimulus that occurs in the substrate in intermittently flooded swamps. Most eggs of An. quadrimaculatus and An. smaragdinus hatch spontaneously in distilled water, but most eggs of An. diluvialis do not. Most An. diluvialis eggs hatch when placed in swamp water or when placed in an infusion of distilled water, leaf litter, and detritus from intermittently flooded swamps, suggesting the presence of an exogenous compound(s) as a hatching factor for this species. Percentage of egg hatch was largest in infusions made from swamp soil and in hexane extracts of swamp water, indicating that the hatching factor is a chemically stable organic substance. Because this phenomenon was not observed with water from lakes, ponds, springs, spring outlet streams, and rivers, An. diluvialis appears to require the hatching factor to facilitate egg hatch when intermittently flooded swamps are inundated. This article reports an exogenous compound being exploited as a hatching stimulus by an Anopheles mosquito.

Nonrecovery of Fertility in Partially Sterile Male Phthorimaea operculella(Lepidoptera: Gelechiidae)

The ability of 150 Gy-irradiated male sperm of the potato tuber moth Phthorimaea operculella (Zeller) to recover their viability after 10 successive matings, or delayed mating for several time intervals was examined. Percentage of egg hatch indicated that neither the repeated mating nor the delayed mating could render the damaged sperm more viable. The irradiation did not influence the mating ability of male potato tuber moth; however, the successive and delayed mating have a great effect on the mating ability of this insect. The current study provided essential information necessary to increase the efficiency of partially sterile male technique as a control method against potato tuber moth.

Susceptibility of potato plants grown from tubers irradiated with stimulation doses of gamma irradiation to potato tuber moth, Phthorimaea operculella Zeller (Lep., Gelechiidae)

The feeding behaviour of potato tuber moth, Phthorimaea operculella Zeller (Lep., Gelechiidae), reared on leaves and tubers of potato plants, which were irradiated as seed (tubers) with stimulation doses of gamma irradiation (1, 3, 5 and 10 Gy), was studied. Significant differences in the larvae and pupae developmental time, pupal weight, mortality, fecundity and percentage egg hatch, were observed between insects fed on plants which resulted from the irradiated seeds and those of the control. It appears that leaves of potato plants grown from irradiated seeds particularly those of 3 Gy, became more attractive to the larvae, although the resulting tubers, with the exception of those of 10 Gy, became more resistant to potato tuber moth. Storing the tubers at ambient temperature conditions affected the degree of larval sensitivity. The leaves and tubers of 10 Gy‐irradiated seeds became more suitable for insect development, indicating that the later dose may inhibit the production of secondary plant metabolities and chemical compounds.

In vitro and in vivo evaluations of a strain of Boophilus microplus (Acari: Ixodidae) selected for resistance to permethrin.

A strain of Boophilus microplus (Canestrini) was selected fro resistance to permethrin by pressuring larvae with increasing doses (range, 0.05-0.35% [AI]) through successive generations (generations F2-F7). At the beginning of the selection process (F2), the pyrethroid resistant (PR) strain was 5.4 times more resistant to permethrin than the pyrethroid susceptible (PS) strain, and the level of resistance increased in each successive generation of the PR strain, reaching a resistance factor (resistance factor) of 20.9 in the F7 generation. Thus, in only 5 generations the level of resistance in the PR strain was increased by 4-fold. The efficacy of permethrin was evaluated by dipping cattle infested with the PS strain and cattle infested with the F7 generation of the PR strain in a vat at 0.057% (AI) (Coopers Animal Health, Mundelein, IL; recommended concentration). Evaluation of the PS strain showed that untreated cattle produced significantly (P < 0.05) more females with a higher index of reproduction than treated cattle. Additionally, biological factors (female weight, egg mass weight, and percent egg hatch) associated with the untreated females were all significantly (P < 0.05) greater than treated females. Conversely, results obtained from the PR strain showed that tick numbers, index of reproduction value, and biological parameters of females in the untreated group were not significantly different (P > 0.05) from those of the treated group. The overall control achieved in the PS strain (99.2%) was significantly higher (P < 0.05) than that of the PR strain (35.7%). The results of the study as they relate to the United States Boophilus Eradication Program are discussed.

Effects of targets impregnated with the chitin synthesis inhibitor triflumuron on the blowfly Lucilia sericata

AbstractThe effects of exposure of adults of the blowfly Lucilia sericata (Meigen) for 24 h to cloth targets impregnated with the chitin synthesis inhibitor triflumuron plus sucrose or sucrose only, were considered. When both male and female L. sericata were exposed to targets treated with sucrose only, the percentage egg hatch varied between 60–75%. When both sexes were exposed to targets treated with 10% triflumuron plus sucrose the percentage egg hatch varied between 3–7%. When females alone were exposed to triflumuron, prior to the introduction of unexposed males, egg hatch varied between 4–14%. The exposure of males alone to 10% triflumuron treated targets, prior to the introduction of unexposed virgin females, did not give any consistent significant decrease in the mean percentage egg hatch. However, repetition of this trial with males exposed to targets treated with 15 or 20% triflumuron, resulted in a percentage egg hatch of 3.1% and 10.3%, respectively. These results suggest that at relatively high target concentrations, males can transfer effective doses of triflumuron to unexposed virgin females.The exposure of adults to triflumuron treated targets did not significantly increase the mortality of either male or female L. sericata. Furthermore, bioassays showed that there was no significant decline in the ovicidal effectiveness of targets treated with 10% triflumuron and sucrose solution following exposure to sun and rain for up to 8 weeks in 1995 and 1996.The results suggest that targets treated with triflumuron suspension concentrate and sucrose may form the basis of an effective system for the control of L. sericata in the field. However, the relatively high concentrations of triflumuron required and the low efficiency with which males are able to transfer effective doses to unexposed females may diminish one of the main theoretical advantages of using a chitin synthesis inhibitor, such as triflumuron, over a conventional insecticide.

Novel Application of Gels as Potential Carriers for Beneficial Insects

Seven agricultural gels were tested as potential carriers for the eggs of 2 predators, Perillus bioculatus (F.) and Podisus maculiventris (Say) (Heteroptera: Pentatomidae). Gels were tested for their effects on egg hatch in petri dishes, covered and uncovered, using 3 viscosities. Egg hatch in petri dishes was generally higher in polyacrylamide gels (Aquastore F and Terra-sorb GB) and starch-based gels (SGP 104K and Waterlock B-100) than in hydroxycellulose-based N-Gel or alginate-based Keltose. Egg hatch was lower in covered versus uncovered dishes, and also lower in high viscosity versus low or medium viscosity gels; however, high viscosities were necessary to stick eggs to plant leaves. Four gels from the petri dish trials were tested on eggplant (Solanum melongena L.) and potato plants (Solanum tuberosum L.) in the greenhouse using both predators. The polyacrylamide gels (Aquastore F and Terra-sorb GB) consistently resulted in the highest percentage batch: hatch rates using these gels were equivalent to the control for P. maculiventris on eggplant, and 19-46% lower than controls on other predator-plant combinations. Hatch data from eggs stored with and without Aquastore F or Terra-sorb GB at 5, 10, or 15°C for 5, 10, or 15 d were compared with those stored at 25°C, with and without gel. Eggs stored in gel did not hatch. Percentage hatch of eggs of both predators stored without gel was lowered by increased storage duration, but was less affected by temperature. Gel amendments (H 2 O 2 and spreader/stickers) decreased hatch rates in gels. Possible explanations for the varying effects of the gels on egg hatch are discussed. Delivery of predator eggs in gels in the future may have practical use in augmentative biological control programs.

Effects of Ozone on Reproduction of Twospotted Spider Mite (Acari: Tetranychidae) on White Clover

Twospotted spider mite, Tetranychus urticae Koch, is a significant pest of peanut, Arachis hypogeae L., that continues to present problems as an induced pest despite recent widespread implementation of IPM practices. Effects of ozone (O3) on reproduction of twospotted spider mites feeding on an O3-sensitive clone and an O3-resistant clone of white clover, Trifolium repens L., were investigated in a greenhouse in continuous-stirred tank reactor chambers. Mite eggs of narrow age distribution (approximately 6 h) were placed on white clover plants exposed to 5 treatment levels of O3. Constant amounts of O3 were added to charcoal-filtered air for 6 h per day to achieve 5 mean concentrations ranging from 10 to 112 nl per liter. Plants were exposed to O3 approximately 9 d before infestation with mites; daily exposures continued for approximately 20 d after mite infestation. The developmental stage of each mite was recorded at approximately 2-d intervals until females were sexually mature (approximately 10 d) and began ovipositing. Thereafter, the cumulative number of eggs produced per mite was recorded. After approximately 5 d of oviposition, each adult mite was removed and the percentage hatch of eggs remaining on each plant was measured for an additional 5 d. Ozone caused more chlorosis and necrosis on the O3-sensitive clover clone than on the O3-resistant clover clone. Increasing O3 levels caused a significant linear decrease in developmental period of the mites. Estimates of time to 1st oviposition decreased linearly with increasing O3. Estimates of time of 1st hatch of 2nd-generation eggs decreased linearly with increasing O3. Elevated O3 levels appear to decrease the time required for female mites to develop from egg to ovipositing adult, which may have a profound effect on the intrinsic rate of population increase. Different responses by mites feeding on resistant plants versus susceptible plants suggests that this is a plant-mediated response.

Chamber Volume Requirements for Reproduction of the ZebrafishDanio rerio

Abstract The zebrafish or zebra danio Danio (=Brachydanio) rerio has recently become a major vertebrate model for the study of developmental biology, neurobiology, and molecular genetics. As a result, most research universities have now invested considerable resources in the construction of large zebrafish facilities. A key element in the design of these facilities is maximizing the efficiency of available space. Here we report on the effects of aquarium chamber volume on the reproduction of zebrafish, with the objective of identifying the minimal volume required for normal egg production. Six adults (two males and four females) were tested in chamber volumes of 500, 400, 300, 200, and 100 mL. Results were compared with those from a control volume of 3.5 L. Eggs were removed from the test chambers after spawning and incubated in petri dishes at 28°C. Total egg production, percent of eggs hatching, and larval length at 96 h postfertilization were used to evaluate breeding success. Compared with the control, egg production was not significantly affected by reduced aquaria volumes of 500, 400, and 300 mL. However, mean egg production from a test volume of 200 mL was only 48% of the control egg production (P < 0.05), and at a test volume of 100 mL, egg production was reduced to 26% of the control value (P < 0.005). Percent egg hatch and 96-h larval length were not affected at any test volume.

Laboratory Infestation of Cotton Bolls by Mediterranean Fruit Fly (Diptera: Tephritidae)

Adults of laboratory-reared Mediterranean fruit fly, Ceratitis capitata (Wiedemann), laid eggs, and mature larvae developed in green intact bolls of cotton, Gossypium hirsutum L., in laboratory cage tests. Cotton bolls collected from early-season plants (102 d old) supported more larvae that developed to pupae (70.07 ±13.13 pupae per kilogram of bolls) (mean ±SEM) than bolls collected from the top (23.34 ±5.66 pupae per kilogram of bolls) and bottom (0 pupae per kilogram of bolls) oflate-season plants (175 d old). Pupal weight and adult emergence was similar among insects reared from bolls collected from either early-season plants (4.4 ±0.7 mg, 23.8 ±13.1% emergence) or the top oflate-season plants (4.5 ±0.3 mg, 30.2 ± 9.6% emergence). The number of eggs laid by adults and percentage egg hatch were similar between adults that had been reared from bolls from early-season plants (47.6 eggs per female, 67.8% hatch) and bolls from the tops oflate-season plants (38 eggs per female, 81.6% hatch).

Tufted Apple Bud Moth Control Tactics for Apple, 1997

Abstract Experimental and registered treatments were applied to replicated 12 to 15 tree plots in a RCB design. Each plot consisted of alternating trees of ‘Yorking’, and ‘Golden Delicious’. These trees were planted to a spacing of 18 X 25 ft and were 18 years old. Experimental sprays were applied with a Friend Airmaster ‘309’ calibrated to deliver either 100 GPA at 2.4 mph or 50 GPA at 2.5 mph. All applications were made as complete sprays except for the second RH-2485 treatment and the Confirm treatments, which were applied as alternate row middle (ARM) applications. Spray timings were based on the accumulation of degree days from first sustained adult moth capture in a sex pheromone trap (13 May) in order to predict various percentages of egg hatch for each brood of TABM. TABM egg hatch data were generated from an adjacent block of apples where TABM egg hatch was monitored on a daily basis throughout the season. Degree day calculations were based on minimum and maximum developmental thresholds of 45°Fand91°F, respectively. Refer to the first table for a listing of treatments, gallonage, method and date of application, and degree day calculations. A routine schedule of fungicides (Benlate 50 DF, Penncozeb 75 DF, Rubigan 1 EC, and Ziram 76 WP) was maintained throughout the experiment. The effect of the sprays on WALH was evaluated by counting the number of nymphs/25 injured leaves/tree (cv. Yorking). Effectiveness of the test chemicals on the ERM, TSSM, and AF was evaluated by counting the mites several times during the season on samples of 25 random leaves/tree (cv. Yorking), 100 leaves/treatment. The cumulative number of mite day s per leaf was calculated for certain treatments from 17 Jun to 12 Aug. The effect of sprays on the predator SP was evaluated by 3-min counts of adults and larvae around the periphery of the same trees. STLM was evaluated by a 5-min count of tissue-feeding mines around the periphery of the trees at the end of each generation. On each sampling date, the total number of mines observed within 5 min regardless of their location on the tree were counted. The number of natural enemies of the spirea aphid were counted in a 5-min examination around the periphery of the center ‘Yorking’ tree. Shelters of the various leafrollers were counted in a 5-min examination of each plot tree on 22 Jul. All larvae were collected and returned to the laboratory for identification. Effectiveness of the treatments on fruit feeders on ‘Golden Delicious’ was assessed by scoring for injury a harvest sample of 100 fruit per tree from each of two center trees per replicate starting on 22 Sep and up to 25 dropped fruit per tree. For ‘Yorking’, injury was assessed on 200 picked fruit per tree from the 2 center trees in each replicate and up to 35 dropped apples per tree starting on 15 Oct. Pest pressure was moderate to heavy throughout the season.

Maternal age and egg weight affect offspring performance in the predatory stink bug Podisus nigrispinus

To investigate influences of maternal age and egg weight on developmental time and body weight of offspring in the Neotropical pentatomid Podisus nigrispinus, a study was carried out using large (0.36 mg) and small (0.32 mg) eggs of young (two-week- old) females and large eggs of old (seven-week-old) females. Incubation period of eggs was influenced only by egg weight, i.e. small eggs took a relatively shorter time to hatch. Both maternal age and egg weight had significant effects on total nymphal and egg-to- adult developmental times. Overall, offspring of young parents had shorter developmental times. None of the developmental periods were significantly affected by sex. No significant differences were found among various offspring groups for percentages of egg hatch, nymphal survival, and sex ratio. Variation of egg weight in relation to the number of eggs per day observed within the first month of life suggests a trade-off between weight of individual eggs and oviposition rate. It is concluded that for mass production of the predators in view of their use in augmentative biocontrol programmes, young parents (2–4 weeks old) should be preferred.