Compatibility of Insect Growth Regulators with Eretmocerus eremicus (Hymenoptera: Aphelinidae) for Whitefly (Homoptera: Alyerodidae) Control on Poinsettias: II. Trials in Commercial Poinsettia Crops

The efficacy and cost of reduced release rates of the parasitoid Eretmocerus eremicus Rose and Zolnerowich (Hymenoptera: Aphelinidae) when combined with application of the insect growth regulator buprofezin were compared to those of a higher parasitoid release rate used alone for whitefly control (Homoptera: Aleyrodidae) on poinsettia (Euphorbia pulcherrima Willd. ex Koltz.). The trial was conducted in seven greenhouses in Methuen, Massachusetts from August through December 1997 and employed commercial poinsettia production practices. Two whiteflies species, Trialeurodes vaporariorum (Westwood) and Bemisia argentifolii Bellows and Perring (= Bemisia tabaci [Gennadius] strain B), were present. Three treatments were examined: (1) E. eremicus used alone at a release rate of three females per plant per week (two greenhouses); (2) E. eremicus at an intermediate release rate of two females per plant per week, combined with mid-season use of buprofezin (two applications, spaced 1 week apart, applied in weeks 9 and 10) (two greenhouses); and (3) E. eremicus at a low release rate of one female per plant per week, combined with mid-season use of buprofezin, applied as in treatment 2 (two greenhouses). In addition, observations were made in one additional greenhouse at the site, in which the grower used pesticides for whitefly control. Prior to the start of the trial, cuttings used for all treatments experienced some pesticide use, first abamectinduring rooting and later buprofezin at potting to reduce whitefly numbers, which were initially very high. At harvest, densities of live whitefly nymphs were not statistically different among the biological control treatments, indicating that a low parasitoid release rate combined with buprofezin was as effective as a higher release rate of the parasitoid used alone. Nymphal densities in separate market samples (based on smaller sample sizes) showed differences among treatments, but all treatments, including the low parasitoid release rate + buprofezin maintained densities of live nymphs + pupae at or below approximately two per leaf, a level commercially acceptable in local markets. Control costs per single-stemmed poinsettia plant were $1.18 for the high parasitoid release treatment, $0.75 for the treatment of weekly releases of two female parasitoids per plant per week + buprofezin, $0.38 for the treatment of releases of one female parasitoid per plant per week + buprofezin, and $0.14 for the chemical control greenhouse.     

Pyriproxyfen controls silverleaf whitefly, Bemisia tabaci (Gennadius), biotype B (Homoptera: Aleyrodidae) (SLW) better than buprofezin in bitter melons Momordica charantia L. (Cucurbitaceae)

To improve compatibility between chemical and biological controls, the use of selective insecticides such as insect growth regulators (IGRs) is crucial. In cucurbits, the use of pyriproxyfen (an IGR) has been shown by others to be an effective method of reducing the number of sap-sucking insects, especially silverleaf whitefly, Bemisia tabaci (Gennadius) Biotype B (SLW). Therefore, we compared pyriproxyfen and buprofezin (an IGR) with that of no treatment (control) in a bitter melon crop for the control of populations of SLW and for their effects on fruit production. Pyriproxyfen controlled SLW and tended to have heavier fruits than the control treatment and reduced the abundance of nymphs and exuvia. Buprofezin showed no evidence in controlling SLW compared with the pyriproxyfen and control treatments. Neither pyriproxyfen nor buprofezin had any effect on the number of harvested fruit or overall fruit yield, but the average weight per fruit was higher than the control treatment. Pyriproxyfen was effective in controlling whitefly populations in bitter melons, and both pyriproxyfen and buprofezin may have the potential to increase yield. Their longer-term use may increase predation by natural enemies as they are species-specific and could favour build up of natural enemies of SLW. Thus, the judicious use of pyriproxyfen may provide an effective alternative to broad-spectrum insecticides in small-scale cucurbit production.     

Parasrnzatlon of bemisia argentifolii (Hom.: Aleyrodidae) by encarsia pergandiella (Hym.: Apheunidae)

The biology of the arrhenotokous autoparasitoid,Encarsia pergandiella Howard, was studied in the laboratory on the silverleaf whitefly,Bemisia argentifolii Bellows & Perring. Egg to adult development of parasitoid females averaged ca. 14 days at about 25.3+0.2?C regardless of whether the whitefly host was reared on tomato, eggplant or squash. While all instars ofB. argentifolii were accepted for primary parasitization, a greater percentage of third and fourth instars were parasitized. Mortality of whitefly nymphs in the absence of parasitization did not differ among instars and averaged about 35%. Second instar to pupal parasitoid females were accepted for secondary parasitization although a greater percent of pupal females were parasitized. About 40% of immatureE. pergandiella females more than 4 days old died in the absence of secondary parasitization when exposed to adultE. pergandiella females.     

Effects of some insect growth regulators on natural enemies of scale insects (Hom.: Coccoidea)

We report and discuss effects of four insect growth regulators: buprofezin, fenoxycarb pyriproxyfen and chlorfluazuron, at concentrations recommended for agricultural use on six species of natural enemies of homopteran pests. Dipping in buprofezin had no appreciable effect on adult mortality, oviposition and development ofComperiella bifasciata (Howard), (Hymenoptera: Encyrtidae). When exposed to hosts treated with buprofezin, percentage mortality of adultEncyrtus infelix Embleton (Encyrtidae) was low; buprofezin had some detrimental effect on immature stages ofE. infelix when applied prior to parasitization, but not when introduced after parasitization. Buprofezin had a slight effect on the immature stages ofCryptochaetum iceryae Williston (Diptera: Cryptochaetidae), while fenoxycarb and pyriproxyfen had marked detrimental effects on parasitization and/or development of the parasitoid fly. None of the larvae ofRodolia cardinalis Mulsant (Coleoptera: Coccinellidae) developed into adults after application of buprofezin, fenoxycarb or pyriproxyfen. Buprofezin and chlorfluazuron completely prevented egg hatch ofChilocorus bipustulatus L. (Coleoptera: Coccinellidae). Buprofezin did not adversely affect egg hatch and larval development ofElatophilus hebraicus Pericart (Hemiptera: Anthocoridae); fenoxycarb or pyriproxyfen applied either before or after oviposition on pine needles caused total suppression of egg hatch.     

Action threshold for applying insect growth regulators to tomato for management of irregular ripening caused by Bemisia argentifolii (Homoptera: Aleyrodidae)

The whitefly Bemisia argentifolii Bellows & Perring is a major pest of tomatoes, causing an irregular ripening disorder characterized externally by incomplete or inhibited reddening of fruit, especially in longitudinal sections, and internally by an increase in the amount of white tissue. Experiments were undertaken during the spring and fall of 1997 and 1998 and the spring of 1999 to develop an action threshold for applying the insect growth regulators (IGRs) buprofezin and pyriproxyfen to manage B. argentifolii and irregular ripening. The IGRs were applied when predetermined thresholds were reached and were compared with a high rate of the systemic insecticide imidacloprid, which was applied at transplanting and provided season-long whitefly control. Only plots treated when the numbers of sessile nymphs (second through fourth instars) reached five per 10 leaflets consistently had both external and internal irregular ripening severity ratings similar to the imidacloprid standard. Results were similar for buprofezin and pyriproxyfen even though the modes of action differ. The five nymphs per 10 leaflets threshold lends itself to field scouting because nymphal counts completed in the field using the unaided eye supplemented with a 10x hand lens were linearly and significantly related to counts completed in the laboratory with a dissecting microscope.     

Poinsettia (Euphorbia pulcherrima Willd Ex Koltz) Cultivar-Mediated Differences in Performance of Five Natural Enemies of Bemisia argentifolii Bellows and Perring, n. sp. (Homoptera: Aleyrodidae)

Laboratory evaluations of five natural enemies of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, n. sp., were conducted to determine their potential as biological control agents in greenhouse poinsettia ranges. Adult longevity, prey consumption or host feeding and parasitism rates, and parasitoid emergence were measured for one predator, Delphastus pusillus LeConte, and four parasitoids, Encarsia formosa Gahan, Encarsia luteola Howard, Encarsia pergandiella Howard, and Encarsia transvena (Timberlake), as possible indicators of efficacy. Characterization of each parameter was performed on two poinsettia cultivars: the first, ′Annette Hegg Brilliant Diamond,′ has trichome densities on the leaf undersurfaces approximately 15% less than the trichome densities on the leaf undersurfaces of the second cultivar, ′Lilo.′ Adult longevity varied significantly between natural enemies (ranging from an average high of 85.2 days for female D. pusillus feeding on B. argentifolii nymphs to an average low of 2.8 days for the Canada colony of E. formosa), but not between cultivar. Prey consumption and oviposition by D. pusillus varied between prey type (nymphs consumed > eggs consumed) and poinsettia cultivar (′Annette Hegg Brilliant Diamond′ > ′Lilo′). Host feeding, parasitism and total number of B. argentifolii nymphs killed varied significantly among Encarsia spp., but no single wasp performed better than the rest across all three parameters. Host feeding, parasitism, and total number of nymphs killed were greater on ′Annette Hegg Brilliant Diamond′ than on ′Lilo′ and this difference was consistent among the four parasitoid species. Among parasitoid species differences in percentage emergence were consistent between the two poinsettia cultivars with emergence from parasitized nymphs on ′Lilo′ being greater than emergence on ′Annette Hegg Brilliant Diamond.′ Results from these evaluations suggest that the probability of achieving successful augmentative biological central will be greater on poinsettia cultivars with fewer trichomes. In addition, achieving biological control is likely to be difficult with releases of E. transvena, but a greater chance for success may be possible through releases of D. pusillus when whitefly densities are high or through releases of E. formosa (Beltsville colony) or mated E. pergandiella independent of whitefly densities.     

Intraguild Predation on the Whitefly Parasitoid Eretmocerus eremicus by the Generalist Predator Geocoris punctipes: A Behavioral Approach

Intraguild predation (IGP) takes place when natural enemies that use similar resources attack each other. The impact of IGP on biological control can be significant if the survival of natural enemy species is disrupted. In the present study, we assessed whether Geocoris punctipes (Hemiptera: Lygaeidae) engages in IGP on Eretmocerus eremicus (Hymenoptera: Aphelinidae) while developing on whitefly nymphs of Trialeurodes vaporariorum (Hemiptera: Aleyrodidae). In choice and non-choice tests, we exposed G. punctipes to parasitized and non-parasitized whitefly nymphs. We found that G. punctipes does practice IGP on E. eremicus. However, choice tests assessing G. punctipes consumption revealed a significant preference for non-parasitized T. vaporariorum nymphs. Subsequently, we investigated whether E. eremicus females modify their foraging behavior when exposed to conditions involving IGP risk. To assess this, we analyzed wasp foraging behavior under the following treatments: i) whitefly nymphs only (control = C), ii) whitefly nymphs previously exposed to a predator ( = PEP) and, iii) whitefly nymphs and presence of a predator ( = PP). In non-choice tests we found that E. eremicus did not significantly modify its number of attacks, attack duration, oviposition duration, or behavior sequences. However, E. eremicus oviposited significantly more eggs in the PEP treatment. In the PP treatment, G. punctipes also preyed upon adult E. eremicus wasps, significantly reducing their number of ovipositions and residence time. When the wasps were studied under choice tests, in which they were exposed simultaneously to all three treatments, the number of attacks and frequency of selection were similar under all treatments. These results indicate that under IGP risk, E. eremicus maintains several behavioral traits, but can also increase its number of ovipositions in the presence of IG-predator cues. We discuss these findings in the context of population dynamics and biological control.     

Toxicity of seven foliar insecticides to four insect parasitoids attacking citrus and cotton pests

Laboratory studies were carried out to compare the toxicity of seven foliar insecticides to four species of adult beneficial insects representing two families of Hymenoptera: Aphelinidae (Aphytis melinus Debach, Eretmocerus eremicus Rose & Zolnerowich, and Encarsiaformosa Gahan) and Mymaridae (Gonatocerus ashmeadi Girault) that attack California red scale, Aonidiella aurantii (Maskell); sweetpotato whitefly, Bemisia tabaci (Gennadius) (both E. eremicus and E. formosa); and glassy-winged sharpshooter, Homalodisca vitripennis (Germar), respectively. Insecticides from four pesticide classes were evaluated using a petri dish bioassay technique across a range of concentrations to develop dosage-mortality regressions. Insecticides tested included acetamiprid (neonicotinoid); chlorpyrifos (organophosphate); bifenthrin, cyfluthrin, and fenpropathrin (pyrethroids); and buprofezin and pyriproxyfen (insect growth regulators [IGRs]). Chlorpyrifos was consistently the most toxic pesticide to all four species of beneficial insects tested based on LC50 values recorded 24 h posttreatment compared with 48-h LC50 values with the neonicotinoid and pyrethroids or 96 h with the IGRs. Among the three pyrethroids, fenpropathrin was usually less toxic (except similar toxicity to A. melinus) than was cyfluthrin, and it was normally less toxic (except similar toxicity with E. formosa) than was bifenthrin. Acetamiprid was generally less toxic than bifenthrin (except similar toxicity with G. ashmeadi). The IGRs buprofezin and pyriproxyfen were usually less toxic than the contact pesticides, but we did not test for possible impacts on female fecundity. For all seven pesticides tested, A. melinus was the most susceptible parasitoid of the four test species. The data presented here will provide pest managers with specific information on the compatibility of select insecticides with natural enemies attacking citrus and cotton, Gossypium hirsutum L., pests.     

Response of late-instar Blattella germanica (Dictyoptera: Blattellidae) to dietary insect growth regulators

Late-instar German cockroaches, Blattella germanica (L.), were used to evaluate the relative effects of single treatments and combinations of three insect growth regulators (IGRs): pyriproxyfen, fenoxycarb, and diflubenzuron. Groups of 15 males or 15 females were held for 2 wk on food treated with varying amounts of IGRs. After removal, newly mature adults were placed with untreated adults of the opposite sex. Mortality, adult phenotype (normal wings, divergent wings, curly wings, and nymphoids), and reproduction were assessed. Mortality occurred largely in the nymphal stage except when all three IGRs were combined. Neither the average number of nymphs per egg case nor hatch of egg cases from phenotypically normal cockroaches (normal wings, occasional darkening of the body) was affected in single treatments or in combinations of two IGRs, but nymphal numbers were reduced when the three IGRs were combined. Hatch from matings of insects with divergent wings varied. At low concentrations (3-10 ppm), hatch was generally normal; at high concentrations, most mating tests were unproductive. Mating tests of cockroaches with curly wings were almost always unproductive. When males with curly wings were mated, females dropped either unfertilized egg cases (no mating) or partially fertilized egg cases. Curly-wing females either dropped unfertilized egg cases or failed to form egg cases because of deleterious effects on ovarian development. Nymphoids did not mate. Diflubenzuron at 100 ppm had no effect other than causing the appearance of a few insects with divergent wings. Effects on phenotype and reproduction began at 3 ppm of both pyriproxyfen and fenoxycarb and at a comparable concentration in the combination of pyriproxyfen + fenoxycarb (1 ppm each). Female sterility was complete at 100 ppm of pyriproxyfen and fenoxycarb. When pyriproxyfen or fenoxycarb was combined with equal amounts of diflubenzuron, the number of productive matings was not reduced at 6 ppm (3 ppm per each IGR). At 20 ppm (10 ppm per each IGR), a reduction in productive matings coincided with the appearance of curly wings. Complete female sterility occurred only at 600 ppm (300 ppm per IGR). The most severe effects occurred in the experiment with equal amounts of pyriproxyfen, fenoxycarb, and diflubenzuron. In addition to reduced hatch from normal phenotypes, this experiment caused complete male sterility (300 ppm; 100 ppm of each IGR). Female sterility was complete at greater than or equal to 90 ppm (30 ppm of each IGR).     

Effect of insecticides on the mortalities of three whitefly parasitoid species, Eretmocerusmundus, Eretmoceruseremicus and Encarsiaformosa (Hymenoptera: Aphelinidae)

The toxicities of 24 insecticides for the biological control of whiteflies were evaluated for Eretmocerus mundus (Mercet), Eretmocerus eremicus Rose and Zolnerowich and Encarsia formosa Gahan using the residual film method (for adults) and the dipping method (for pupae). Mortalities from insect growth regulators (IGRs) (flufenoxuron and lufenuron), Bacillus thuringiensis (Bt), pymetrozine and sulfur were <30% for both pupae and adults of all three species, indicating that the parasitoids were not seriously affected by these insecticides. Neonicotinoids (acetamiprid, clothianidin, dinotefuran, imidacloprid and nitenpyram), synthetic pyrethroids (etofenprox and permethrin), organophosphates (acephate and fenitrothion), chlorphenapyr, emamectin benzoate, spinosad and tolfenpyrad were seriously harmful (100% mortality) and acaricides (chinomethionat, milbemectin and pyridaben) were moderately harmful or seriously harmful to adult parasitoids (leading to mortalities of >92%). For each insecticide, the mortality of pupae was generally lower than that of adults, even though the toxicity classification for the two groups was similar. The results indicate that IGRs, Bt, pymetrozine and sulfur are relatively harmless, and are compatible with the use of parasitoids to help control whiteflies for integrated pest management in greenhouses.     

Population suppression of Bemisia tabaci (Hemiptera: Aleyrodidae) using yellow sticky traps and Eretmocerus nr. rajasthanicus (Hymenoptera: Aphelinidae) on tomato plants in greenhouses

We conducted three experiments for management of Bemisia tabaci (Gennadius) biotype ‘B’ on tomatoes under greenhouse conditions: (i) vertically placing yellow sticky cards either parallel or perpendicular to tomato rows at a rate of 1 per 3‐m row; (ii) releasing Eretmocerus sp. nr. rajasthanicus once at 30 adults/m² in the high whitefly density greenhouses (> 10 adults/plant), or twice at 15 adults/m² at a 5‐day interval in the low whitefly density greenhouses (< 10 adults/plant); and (iii) using combinations of yellow sticky cards that were placed vertically parallel to tomato rows and parasitoids released once at 30/m² in high whitefly density greenhouses or twice at 15/m² at a 5‐day interval in low whitefly density greenhouses. Our data show that yellow sticky cards trapped B. tabaci adults and significantly reduced whitefly populations on tomato. The yellow sticky cards that were placed parallel to tomato rows caught significantly more whitefly adults than those placed perpendicular to tomato rows on every sampling date. In the treatment where parasitoids were released once at 30/m² in high whitefly density greenhouses, the number of live whitefly nymphs were reduced from 4.6/leaf to 2.9/leaf in 40 days as compared with those on untreated plants on which live whitefly nymphs increased from 4.4/leaf to 8.9/leaf. In the treatment where parasitoids were released twice at 15/m² in low whitefly density greenhouses, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 2.1/leaf to 1.7/leaf in 20 days as compared with those on untreated plants on which numbers of live nymphs of B. tabaci increased from 2.2/leaf to 4.5/leaf. In the treatment of yellow sticky cards and parasitoid release once at 30/m² in high whitefly density greenhouses, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 7.2/leaf to 1.9/leaf, and in the treatment of yellow sticky cards and parasitoid release twice at 15/m² at a 5‐day interval at low whitefly density, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 2.5/leaf to 0.8/leaf; whereas the numbers of live nymphs of B. tabaci on untreated plants increased from 4.4/leaf to 8.9/leaf. An integrated program for management of B. tabaci on greenhouse vegetables by using yellow sticky cards, parasitoids and biorational insecticides is discussed.     

Effect of the primary host for production of both sexes on the mating interaction in an autoparasitoid species

Encarsia sophia (Girault and Dodd) is an autoparasitoid in the hymenopteran family Aphelinidae. The females develop as primary parasitoids on whitefly nymphs (primary hosts), whereas the males develop as hyperparasitoids on their own species or on other primary parasitoid species (secondary hosts). The autoparasitoids not only parasitise whiteflies but also kill them with strong host-feeding capacity. In this study, female and male E. sophia were reared on the primary hosts Trialeurodes vaporariorum and Bemisia tabaci ‘Q’, and the host-feeding and parasitism of wasps on both whitefly species were determined for the four possible different mating combinations: (i) E. sophia females reared on B. tabaci (ESF-BT) mated with E. sophia males from B. tabaci (ESM-BT), (ii) E. sophia females reared on T. vaporariorum (ESF-TV) mated with E. sophia males from T. vaporariorum (ESM-TV), (iii) ESF-BT mated with ESM-TV, and (iv) ESF-TV mated with ESM-BT. ESF-TV mated with ESM-TV killed the largest percentage of whitefly nymphs through host feeding. The ESF-TV with larger body size mating with larger ESM-TV killed more whitefly nymphs through host feeding than those mating with smaller ESM-BT. Whether B. tabaci or T. vaporariorum were used as hosts, ESF-TV mated with ESM-TV and ESM-BT and ESF-BT mated with ESM-BT significantly parasitised more whitefly nymphs than ESF-BT mated with ESM-TV. In general, ESF-BT mated with ESM-TV killed significantly fewer whitefly nymphs through parasitism and host feeding than the other three mating combinations on both whitefly species. These results indicated that the performance of autoparasitoids on insect pests was not only dependent on females but was also affected by mating with males from different primary host species.     

Effects of three insecticides on adult bionomics of the parasitoid Encarsia formosa

Pesticides can negatively affect many life history traits of natural enemies. In this study, we studied the effects of three insecticides with different modes of action on the bionomics of Encarsia formosa, a parasitoid of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Buprofezin (800 mg (a.i.)/L) and pyriproxyfen (50 mg (a.i.)/L) were selected among IGRs, while fenpropathrin (250 mg (a.i.)/L) was selected from the Pyrotheroids. Adults of E. formosa were treated via exposure to residues of insecticides on leaf discs. Our results revealed that buprofezin and pyriproxyfen did not affect longevity and fecundity, while fenpropathrin significantly reduced the longevity and fecundity of treated wasps. Results of logistic regression revealed that control, buprofezin- and pryproxyphen-treated E. formosa was a function of host density and followed a type II functional response. In contrast, E. formosa treated by fenpropathrin showed a type III functional response. Estimated attack rate for buprofezin and pyriproxyfen did not differ significantly from the control, whereas fenpropathrin-treated wasps showed a lower attack rate than the control. According to the obtained results, handling time of fenpropathrin-treated wasps was significantly higher (4.57 ± 0.5) than the control (2.83 ± 0.35). Our results showed that the maximum parasitism rate achieved by control wasps was 8.39, while the rate for buprofezin-, pyriproxyfen- and fenpropathrin-treated wasps was 6.99, 7.69 and 5.25, respectively. Overall, results suggest that buprofezin and pyriproxyfen can be used in an integrated pest management programme or biological control programme without destructive effects on the efficiency of this natural enemy in green houses.     

Effects on German cockroach nymphs of contact exposure to IGRs, singly and in combination

Late instar German cockroach male and female nymphs were exposed continuously for two weeks to surfaces treated with fenoxycarb, diflubenzuron, and pyriproxyfen, singly and in combination. Concentrations were determined that eliminated or nearly eliminated reproduction in matings with untreated mates, either through mortality, effects on reproduction, or a combination of mortality and sterility (no hatch). The major effect of fenoxycarb, pyriproxyfen, and pyriproxyfen plus fenoxycarb was on reproduction. The major effect of diflubenzuron was mortality. No hatch occurred in matings of females that were exposed to low concentrations of pyriproxyfen and fenoxycarb (2 ng/cm² and 6 ng/cm², respectively); sterility was incomplete when females were exposed to 600 ng/cm² of diflubenzuron. Mortality and sterility acted together to eliminate productive matings (matings that produced nymphs) when relatively high concentrations of diflubenzuron were combined with one or both of the other insect growth regulators (IGRs). In the triple combination, very small amounts of fenoxycarb and pyriproxyfen (total 1.1 ng/cm²) combined with 200 ng/cm² of diflubenzuron eliminated productive matings of treated females, but similar results with treated males were found only at higher concentrations of each IGR.     

Impact of Eretmocerus eremicus (Hymenoptera: Aphelinidae) on open-field Bemisia tabaci (Hemiptera: Aleyrodidae) populations

The effect of three different release rates (1×, 10×, and 20× the recommended rate of 25,000/ha) of Eretmocerus eremicus Rose and Zolnerowich on Bemisia tabaci (Gennadius) populations found in open-field cantaloupe, Cucumis melo L., was evaluated against populations in untreated control plots. Parasitoids were released from a point source in the center of each of nine treatment plots. Whitefly population growth, encompassing all developmental stages, and rates of parasitism were monitored within a 10-m annulus surrounding the center point in all 12 plots over a 52-d period. The rates of B. tabaci population increase during this time were equivalent regardless of the parasitoid release rate. Whitefly densities were not limited in any of our treatment plots when compared to those found in the control plots. Moreover, mean rates of parasitism did not increase with time nor did they differ among the three treatments or control plots (7.9 ± 6.5%). Finally, estimated rates of parasitism were density-dependent responding positively to increasing host numbers. The ineffectiveness of this parasitoid in controlling whitefly populations in the field may be due to its high propensity to disperse at low host densities or to influxes of immigrating whiteflies. Hence, the use of E. eremicus alone is not an efficient means to reduce whitefly populations in melon crops in the southwestern United States.     

Functional response and mutual interference of Peristenus spretus (Hymenoptera: Braconidae), a parasitoid of Apolygus lucorum (Heteroptera: Miridae)

Peristenus spretus Chen & van Achterberg (Hymenoptera: Braconidae) is a solitary endoparasitoid, which is considered for augmentative biological control of Apolygus lucorum Meyer-Dür (Heteroptera: Miridae) in Chinese cotton fields. Since the association of P. spretus with A. lucorum was only recently discovered, the biology of the parasitoid remains unknown. In order to understand its reproductive biology, the mutual interference and functional response of P. spretus were investigated by altering either the parasitoid or the host density while keeping the other constant. In both experiments, the effects of parasitoid and host densities on parasitism, superparasitism, progeny production and sex ratio were assessed. P. spretus exhibited a Holling type II functional response to changing host densities, indicating that parasitism increases with increasing host density until the parasitoid reaches its maximum reproductive capacity. The model suggested that a single P. spretus female could parasitise a maximum of 88 nymphs per day or four nymphs per hour. Increasing the wasp-nymph ratio from 1:10 to 1:80 significantly increased the offspring production more than fivefold from ±5.8 to ±35.6; further increasing the host densities (above 80 nymphs) did not significantly increase offspring production. Strong mutual interference of foraging P. spretus females occurred only at high parasitoid densities. Parasitoids foraging alone produced an average progeny of 33.4, whereas parasitoids foraging in groups of 16 produced only 2.6. The optimal wasp-nymph ratio for mass-rearing P. spretus is 4:100, given that resources of parasitoids and nymphs are unlimited.     

Nectar provisioning close to host patches increases parasitoid recruitment,retention and host parasitism

In the adult stage, many parasitoids require hosts for their offspring growth and plant-derived food for their survival and metabolic needs. In agricultural fields, nectar provisioning can enhance biological control by increasing the longevity and fecundity of many species of parasitoids. Provided in a host patch, nectar can also increase patch quality for parasitoids and affect their foraging decisions, patch time residence, patch preference or offspring allocation. The aim of this study was to investigate the impact of extrafloral nectar (EFN) provisioning close to hosts on parasitoid aggregation in patches. The aphid parasitoid Diaeretiella rapae (M’Intosh) was released inside or outside patches containing Brassica napus L. infested by Brevicoryne brassicae L. aphids and Vicia faba L. with or without EFN. When parasitoids were released outside patches, more parasitoids were observed in patches with EFN than in patches deprived of EFN. This higher recruitment could be linked to a higher attraction of a combination of host and food stimuli or a learning process. A release–recapture experiment of labeled parasitoids released within patches showed the higher retention of parasitoids in patches providing EFN and hosts, suggesting that food close to the host patch affects patch residence time. Both attractiveness and patch retention could be involved in the higher number of parasitoids foraging in host patches surrounded by nectar and for the higher parasitism recorded. Nectar provisioning in host patches also affected female offspring allocation inside the patch.     

Role of two insect growth regulators in integrated pest management of citrus scales

Portions of two commercial citrus orchards were treated for two consecutive years with buprofezin or three consecutive years with pyriproxyfen in a replicated plot design to determine the long-term impact of these insect growth regulators (IGRs) on the San Joaquin Valley California integrated pest management program. Pyriproxyfen reduced the target pest, California red scale, Aonidiella aurantii Maskell, to nondetectable levels on leaf samples approximately 4 mo after treatment. Pyriproxyfen treatments reduced the California red scale parasitoid Aphytis melinus DeBach to a greater extent than the parasitoid Comperiella bifasciata Howard collected on sticky cards. Treatments of lemons Citrus limon (L.) Burm. f. infested with scale parasitized by A. melinus showed only 33% direct mortality of the parasitoid, suggesting the population reduction observed on sticky cards was due to low host density. Three years of pyriproxyfen treatments did not maintain citricola scale, Coccus pseudomagnoliarum (Kuwana), below the treatment threshold and cottony cushion scale, Icerya purchasi Maskell, was slowly but incompletely controlled. Buprofezin reduced California red scale to very low but detectable levels approximately 5 mo after treatment. Buprofezin treatments resulted in similar levels of reduction of the two parasitoids A. melinus and C. bifasciata collected on sticky cards. Treatments of lemons infested with scale parasitized by A. melinus showed only 7% mortality of the parasitoids, suggesting the population reduction observed on sticky cards was due to low host density. Citricola scale was not present in this orchard, and cottony cushion scale was slowly and incompletely controlled by buprofezin. These field plots demonstrated that IGRs can act as organophosphate insecticide replacements for California red scale control; however, their narrower spectrum of activity and disruption of coccinellid beetles can allow other scale species to attain primary pest status.     

Discovery and utilization of Bemisia argentifolii patches by Eretmocerus eremicus and Encarsia formosa (Beltsville strain) in greenhouses

The ability of two species of aphelinid parasitoids to find and attack Bemisia argentifolii was determined. Experiments were conducted with whitefly patches on single leaf poinsettia plants randomly distributed in canopies of four commercially grown poinsettia crops at an early and late stage of plant growth. Eretmocerus eremicus found experimental patches in canopies of small and large plants more quickly and frequently, and killed more nymphs following patch discovery than Encarsia formosa (Beltsville strain). E. eremicus exhibited a Type I functional response in small and large canopies while E. formosa (Beltsville strain) showed a Type II functional response in small canopies and a weak linear response in large canopies. In greenhouses treated with E. eremicus, canopy size increased 4.6× and nymphs per plant increased 14.2× between small and large canopy experiments. Consequently, area of search for this parasitoid increased 83%, number of wasps counted on patches decreased 74%, and proportion of nymphs killed in artificial patches decreased 47% between small and large canopies. In greenhouses treated with E. formosa Beltsville strain, canopy size increased 7.3× and nymphs per plant increased 25.4× between small and large canopy experiments. Consequently for E. formosa Beltsville strain, area of search increased 11%, number of wasps counted on patches decreased 86%, and proportion of nymphs killed in artificial patches decreased 47% between small and large canopies.     

Biology of a thelyotokous biotype of Eretmocerus mundus (Hymenoptera: Aphelinidae) on Bemisia tabaci (Homoptera: Aleyrodidae)

Abstract Thelyotokous biotype of Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae), a parasitoid of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was recently recorded in northern Iran. Reproductive biology of this biotype was studied as part of an evaluation of its potential for biological control of B. tabaci. The parasitoid deposited more eggs under 2nd and 3rd nymphal instars than 1st or 4th instars. Adult females fed honey, with no access to whitefly nymphs, lived significantly longer (13.6 ± 4.7 d) than those given access to nymphs, but not fed honey (7.6 ± 2.21 d). Lifetime fecundity averaged 81.7 ± 26.9 female progeny per female parasitoid, ranging from 11–132. Daily fecundity, measured as the number of whitefly nymphs parasitized by per female each day for 10 d, averaged 18.06 ± 3.95 for the first 6 d of life, and then declined to < 11. Developmental time from oviposition to parasitoid emergence was significantly shorter in the 3rd instar of the host (15.9 ± 1.06 d) than in the 1st instar (18.7 ± 2.3 d), but not in the 2nd instar (16.4 ± 1.3 d).