Study on some biological characteristics of Tetrastichus gallerucae (Hym. Eulophidae), important parasitoid of Elm leaf beetle eggs in Kerman,Iran

In this study, a number of biologic characteristics of Tetrastichus gallerucae, the most important natural enemy of Xanthogaleruca luteola (Col.: Chrysomellidae), were studied. Experiments were carried out in growth room with a temperature of 25°C±1°C, relative humidity of 60%±5% and light period of 16L:8D. The results demonstrated the following outcomes: without food and host egg, the longevity of male and female bees was respectively, 1.23 and 1.35 days. On the host egg, their longevities were 3.85 and 6.02 days, respectively. On rarefied honey their longevities were 14.04 and 24.74 days, respectively and on the host eggs together with rarefied honey, their longevities were 13.4 and 34.72 days, respectively. The average growth period times in the egg of elm leaf beetle of male and female bees were 12.97 and 12.63 days, respectively. The percentage of female bees decreases as the longevity of the insects increases. These bees lay eggs in the 1–9-day-old eggs of elm leaf beetle but 1-day-old eggs of the host are preferred by T. gallerucae.     

Host location in Oomyzus gallerucae (Hymenoptera: Eulophidae), an egg parasitoid of the elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Eggs of the elm leaf beetle Xanthogaleruca luteola are often heavily attacked by the chalcidoid wasp Oomyzus gallerucae. We studied the chemical signals mediating interactions between the egg parasitoid, its host, and the plant Ulmus campestris. Olfactometer bioassays with O. gallerucae showed that volatiles of the host-plant complex attract the parasitoid. In order to determine the source of attractive volatiles within this host-plant-complex, we tested separately the effect of odours of eggs, gravid elm leaf beetle females, faeces of the beetles and elm twigs (with undamaged leaves and leaves damaged either mechanically or by feeding of the beetles). Odours of faeces of the elm leaf beetle were attractive, whereas neither volatiles from eggs nor from gravid females acted as attractants. Volatiles from undamaged or damaged plants did not elicit a positive reaction in O. gallerucae, whereas volatiles from feeding-damaged plants onto which host eggs had been deposited were attractive. This latter result suggests that it is not feeding but deposition of host eggs onto elm leaves that induces the production of plant volatiles attractive to the egg parasitoid. Investigations of the search patterns of O. gallerucae within the habitat by laboratory bioassays revealed that the egg parasitoid encounters host eggs by chance. Contact kairomones from faeces were demonstrated to be important in microhabitat acceptance, while contact kairomones isolated from the host eggs are relevant for host recognition. Received: 12 February 1997 / Accepted: 29 April 1997     

RearingTetrastichus gallerucae [hymenoptera: Eulophidae] for biological control of the ELM leaf beetleXanthogaleruca luteola

Tetrastichus gallerucae (Fonscolombe) was collected in southern France in 1985 and is being reared at the Division of Biological Control in Albany, Ca for use against the elm leaf beetle (ELB),Xanthogaleruca luteola (Müller) in northern California. This egg parasitoid can be reared easily by keeping the beetle eggs on a moist substrate to prevent desiccation and by inhibiting the growth of mold with air currents. A laboratory colony of ELB adults provides a constant supply of fresh eggs for the parasitoids. In 1985 and 1986 over 80,000T. gallerucae were released at 17 sites.      

Specificity of chemical cues used by a specialist egg parasitoid during host location

Plant synomones and host kairomones are known to guide the egg parasitoid Oomyzus gallerucae to its specific host, the elm leaf beetle Xanthogaleruca luteola (= Pyrrhalta) (Muller) feeding upon elm leaves (Ulmus spp.). In this study, we investigated whether the activities of these plant synomones and kairomones are specific for the plant and herbivore species, respectively. Olfactometer and contact bioassays were used. In habitat location, O. gallerucae (Fonscolombe) is known to use synomones from Ulmus minor (Miller) that are induced by egg depositions of X. luteola. The attractiveness of such induced volatiles was shown to be specific both for the Ulmus species and the herbivore species depositing eggs. Neither leaves of U. glabra Hudson (= U. montana) carrying eggs of X. luteola nor leaves of U. minor (= U. campestris = U. procera) carrying eggs of the chrysomelid species Galeruca tanaceti L. emitted attractive synomones. O. gallerucae is also known to be attracted by volatile kairomones from faeces of X. luteola feeding on U. minor and to show prolonged antennal drumming when contacting substrates contaminated with these faeces. The kairomonal activity of the faeces was proved to be independent of the Ulmus species, since also faeces from elm leaf beetles feeding upon U. glabra emitted attractive volatiles. However, the faecal kairomones were specific for the herbivorous species, since faeces from a lepidopteran larva (Opisthograptis luteolata L.) feeding upon elm hardly elicited any antennal drumming in O. gallerucae. The egg parasitoid studied is known to recognize host eggs of X. luteola by contact kairomones extractable from the egg shell. O. gallerucae clearly differentiated between host eggs and eggs of another closely related chrysomelid species, Galerucella lineola L., as was shown by comparing duration of antennal drumming on host eggs and eggs of G. lineola.     

Response of the elm leaf beetle to host plants induced by oviposition and feeding: the infestation rate matters

We investigated by olfactometry and feeding‐ and oviposition‐choice‐tests how the highly specialised elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), responds to conspecifically induced defences in the field elm Ulmus minor Miller (Ulmaceae). While egg deposition of the beetle induced elms to release volatiles attractive to the egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae), feeding alone did not. In the present study, females of the elm leaf beetle showed preferences for the odours of twigs induced by low egg deposition and feeding over odours from uninfested twigs. In contrast, heavy infestation rendered elm odours less attractive to the beetles. Feeding and oviposition bioassays revealed an oviposition preference for leaves from uninfested twigs when compared to locally infested leaves. However, beetles preferred to feed upon systemically induced leaves compared to uninfested ones. The different preferences of the elm leaf beetle during host plant approach might be explained by a strategy that accounts for both gaining access to high quality nutrition and avoiding competition or parasitism.     

Insecticidal and biological efficacy of two vegetable oils against Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) under laboratory conditions

Bioefficacy of two vegetable oils, namely ethyl oleate and Acorus calamus, were conducted against the pulse beetle Callosobruchus maculatus (Fabr.) under a constant temperature of 29 ± 1 °C and a relative humidity of 65 ± 5% R.H. Four concentrations (0.125, 0.25, 0.5 and 1.0%) of each oil were used against the adult and tested their latent effect on the immature stages of the beetle. The results obtained show insecticidal effect of both ethyl oleate and A. calamus oil; however, A. calamus oil proved to be more toxic to the adults at all the concentrations tested in comparison to the ethyl oleate oil. As the concentration of the oils decreased, the percentage mortality decreased. The obtained results concentrated on biological efficacy of the oils tested against the adults. Both oils affected the longevities of both male and female C. maculatus adults in comparison to the control. The oviposition periods of the adult female were affected significantly in comparison to the control. A. calamus oil prohibited oviposition completely at high concentrations of 0.5 and 1.0% and caused complete sterility to the females. Lower concentrations decreased the oviposition period greatly and reduced the number of eggs laid in comparison to the control. Ethyl oleate had an inconsiderable latent effect on the incubation period as well as the percentage of hatching of the resulting eggs. A. calamus oil decreased the percentage of egg hatchability with serious increase in the percent sterility. The two tested oils had slight extension in either larval or pupal stage of the resulting progeny of C. maculatus. Both oils show oviposition deterrency towards C. maculatus adults. The oviposition deterrent index was 100% when mung bean seeds were treated with A. calamus oil. The bruchid females laid all eggs on control seeds and no eggs were laid on treated seeds.     

Host-stage preference and functional response of aphid parasitoid Diaeretiella rapae (McIntosh) (Hym.: Braconidae) on greenbug,Schizaphis graminum (Rondani) (Hem: Aphididae)

Searching capacity is of great importance in the efficiency of natural enemies. In this research, the host-stage preference and functional response of Diaeretiella rapae (McIntosh) to different densities of greenbug, Schizaphis graminum (Rondani) were determined on Pishtaz wheat leaves at 25 ± 1°C, 60–70% relative humidity, and a photoperiod of 16:8 h (L:D). The host-stage preference was investigated by exposing 60 number of all nymphal instars and adults of greenbug to individual parasitoid females at eight replicates. Results indicated significant preference of D. rapae to second instar nymphs of S. graminum to perform functional response experiment. Densities of 2, 4, 8, 16, 32, 50, 64, 90 and 130 second instar nymphs of greenbugs were exposed to individual mated female wasps at 10 replicates for 24 h. Type of functional response was determined by logistic regression and its parameters, searching efficiency (a) and handling time (T _h), were estimated by non linear regression. The results indicated that the functional response of D. rapae was type III and values of searching efficiency, handling time and maximum rate of parasitism were calculated by two models as 0.1364 ± 0.084, 0.5761 ± 0.0179, 41.6594; 0.06489 ± 0.00652 (h^?1), 0.5628 ± 0.0173 (h) and 42.6439 (aphids/parasitoid/day), respectively.     

Seasonal patterns of the thermal response in relation to sugar and polyol accumulation in overwintering adults of elm leaf beetle, Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Elm leaf beetle, Xanthogaleruca luteola (Muller), is one of the key pests of elm trees that survive winter in reproductive diapause in sheltered locations. Overwintering adults of the elm leaf beetle showed a complex sugar/polyol cryoprotectant system. The major components of the multiple systems were glucose, myo-inositol and trehalose. In this study, we investigated the seasonal profile of low molecular weight compounds and glycogen in natural population and also in response to thermal constant regimes (5 and 15 °C). Among these components, a remarkable seasonal pattern of accumulation/depletion was observed in myo-inositol over the course of hibernation with the development of diapause progress. Incubating at 5 °C only elicited a strong response in myo-inositol synthesis during diapause. It suggests that the elm leaf beetle accumulates myo-inositol not only in relation to entering diapause but also in response to low temperatures and their interactions. The laboratory acclimation experiments showed that adults exposed to 15 °C had no chance for accumulation of low molecular weight carbohydrate even during diapause. The results of this study illustrated that overwintering adults of elm leaf beetle produce myo-inositol as the primary substance which plays a specific role in some biochemical adjustments in overwintering adults of X. luteola.     

Functional response of Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae) to Bemisia tabaci (Gennadius) on tomato leaves

Bemisia tabaci (Gennadius) is an important invasive pest of vegetables and other horticultural plants worldwide. In this study, the functional response of Neoseiulus cucumeris (Oudemans) to different stages of immature B. tabaci was evaluated under laboratory conditions. Predation experiments were conducted on tomato leaf discs (2.5?cm diameter) over a 24-h period at 26?±?1°C and 65?±?5% relative humidity with a L16:D8 photoperiod. The prey densities ranged from 5 to 90 immature stages (eggs and first- to fourth-instar nymphs) of B. tabaci per leaf disc. The results showed that the egg stage of B. tabaci was the most susceptible prey stage and that the mated female adult mite (3-day-old) was a more effective predator than the male adult mite. The functional response of adult N. cucumeris followed a Type II trend curve as shown in a logistic regression model. Adult N. cucumeris exhibited different predation tendencies towards prey in different stages of immaturity. The daily maximum number of eggs, first-, second- and third-instar nymphs of B. tabaci killed by a single female over a 24-h period (26?±?1°C, 65?±?5% RH and L16:D8 photoperiod) were 8.5, 5.2, 3.0 and 2.1, respectively, whereas the number killed by a single male was 6.0, 4.0, 2.3 and 1.8, respectively. The results of this study could help determine an effective B. tabaci biocontrol measure that employs a natural predator.     

Patch-exploitation patterns in an egg parasite of elm leaf beetle

Eggs of elm beetle,Pyrrhalta luteola (Muller), normally occur in masses which can be viewed as discrete host patches in space and time. Analysis of>800 egg masses from 3 field sites in northern California revealed that the number of eggs/mass varied from 2 to>40 and that the imported egg parasiteTetrastichus gallerucae (Fonsc.) exploited a relatively large proported of the egg masses at certain times. The spatial relationship between parasitization and number of eggs/egg mass was assessed in 2 ways-i.e., for exploited masses only and for all masses combined (exploited+nonexploited). Percent parasitization was density independent in most cases for both data sets. It is suggested that both methods of analysis can provide patterns which are relevant to biological control of insect pests.      

Smelling the tree and the forest: elm background odours affect egg parasitoid orientation to herbivore induced terpenoids

Parasitic insects use herbivore induced plant volatiles as signals for host location. However, their responses to these volatiles in the background of natural habitat odours need further evaluation for developing successful biological control strategies. Field elms (Ulmus minor Miller (Ulmaceae)) release a blend of volatiles in response to oviposition of the elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), a major urban and forest pest in the USA and Australia. This induced blend attracts the beneficial egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae). Our olfactory assays showed that an odorous background of non-attractive host plant volatiles from feeding damaged elms or (Z)-3-hexenyl acetate masks the attractive effect of the host-induced (E)-β-caryophyllene to O. gallerucae. Quantitative GC–MS analyses revealed decreased concentrations of (Z)-3-hexenyl acetate accompanied by highly increased concentrations of sesquiterpenes in oviposition and feeding treated elms compared to undamaged elms. This finding hints to how the parasitoid might distinguish between different odorous backgrounds. It is corroborated by the outcome of our field study in natural elm stands, where the egg parasitoid parasitized more host egg masses due to an artificially induced blend of elm terpenoids.     

Prominence of three diets on life table parameters for Chrysoperla carnea (Neuroptera: Chrysopidae) to mass rearing under laboratory conditions

Chrysoperla carnea (Steph.) is a general predator reared in industrial scale. Different eggs of moth were used to rear C. carnea, but stabled moth colony needed expensive equipment and is costly. In this research, we surveyed appropriate diet to mass rearing. For this purpose, 100 same old (24H) eggs of C. carnea, separately, were selected randomly from the mass culture of C. carnea which was reared on the egg of flour moth Anagasta kuehniella (Zeller), artificial diet and semi-artificial diet under laboratory conditions (25 ± 5°C, 65 ± 5% RH and L–D: 16–8). These results showed reduction process e_x (expectation of life table at age X) and the survival curve was convex (K-Strategy). Also L_x in appearing of adults that fed on egg of flour moth, artificial diet and semi-artificial diet were 0.76, 0.4 and 0.9 which implied that 24, 60 and 10% of cohort were dead before reaching adult stage. Eggs produced by each female were recorded daily until all females died. The parameters were estimated using Carey’s (1993) method. Gross (GRR) and net (R₀) reproductive rates of predator on A. kuehniella, artificial diet and semi artificial diets were 225.5 ± 3.45, 72.4 ± 3.5, 267.8 ± 4.8 and 180.12 ± 2.3, 24.33 ± 4.3, 254.05+3.3 (female/female/generation), respectively. Mean generation time (T), Doubling time (DT), Intrinsic rate of increase (r_m ) and Finite rate of increase (λ) of predator on A. kuehniella, artificial diet and semi artificial diet were 31.9 ± 0.71, 42.87 ± 0.45, 29.79 ± 0.57 (days); 4.27 ± 0.03, 9.36 ± 0.06, 3.74 ± 0.05 (days); 0.162 ± 0.001, 0.074 ± 0.003, 1.185 ± 0.002; and 1.175 ± 0.001, 1.076 ± 0.002, 1.203 ± 0.002 (female/female/day), respectively. This research indicated that semi-artificial diet is a suitable prey for the predator.     

Functional response of Chrysoperla carnea (Neuroptera: Chrysopidae) to Helicoverpa armigera (Lepidoptera: Noctuidae): Effect of prey and predator stages

Abstract Understanding predator–prey interactions has a pivotal role in biological control programs. This study evaluated the functional response of three larval instars of the green lacewing, Chrysoperla carnea (Stephens), preying upon eggs and first instar larvae of the cotton bollworm, Helicoverpa armigera Hübner. The first and second instar larvae of C. carnea exhibited type II functional responses against both prey stages. However, the third instar larvae of C. carnea showed a type II functional response to the first instar larvae of H. armigera, but a type III functional response to the eggs. For the first instar larvae of C. carnea, the attack rate on H. armigera eggs was significantly higher than that on the larvae, whereas the attack rate of the second instar C. carnea on H. armigera larvae was significantly higher than that on the eggs. For the third instar larvae of C. carnea, the attack rate on the larvae was 1.015 ± 0.278/h, and the attack coefficient on the eggs was 0.036 ± 0.005. The handling times of the third instar larvae on larvae and eggs were 0.087 ± 0.009 and 0.071 ± 0.001 h, respectively. The highest predation rate was found for the third instar larvae of C. carnea on H. armigera eggs. Results of this study revealed that the larvae of C. carnea, especially the third instar, had a good predation potential in controlling H. armigera eggs and larvae. However, for a comprehensive estimation of the bio‐control abilities of C. carnea toward H. armigera, further field‐based studies are needed.     

Role of different habitats for the functional response of Crytorrhinus lividipennis (Hemiptera: Miridae) on Nilaparvata lugens (Hemiptera: Delphacidae)

The functional response of a predator, Cyrtorrhinus lividipennis, on the brown planthopper, Nilaparvata lugens, was investigated in two different experimental habitats: a piece of tiller in a petri dish (5.5?cm in diameter) and a rice plant in a net cage (5.5?cm diameter?×?43?cm height) for 24?h at room temperature. In the petri dish experiment, 2nd–5th instar nymphs, adult male, and female C. lividipennis were introduced in separate experiments to eggs of N. lugens at densities of five, 10, 20, 30, and 40 eggs per piece of rice. In the rice plant experiment, each C. lividipennis was introduced to a cage with a rice plant containing N. lugens eggs. After 24?h, the number of dead eggs and remaining eggs were counted and data fitted to three functional response models. Among the three types of functional responses, Type II best described the predator response to host densities in N. lugens in both experimental habitats, according to the logistic regression analysis value. The results showed that C. lividipennis was a more effective predator in the rice plant experiment compared to the disc experiment. Additionally, the searching efficiency and handling time parameters were different in the two different experimental habitats. This may cause errors when applying the functional response to biological control and predator–prey models. Different habitats and other environmental conditions from the experiment and natural rice field have to be considered.     

Functional response of Macrolophus pygmaeus (Rambur) and Nesidiocoris tenuis (Reuter) feeding on two different prey species

Functional response type and predatory parameters of Macrolophus pygmaeus and Nesidiocoris tenuis (Hemiptera: Miridae), the two important predators widely used in IPM programmes at tomato greenhouses, were investigated. The predators fed on Tuta absoluta (Lepidoptera: Gelechiidae) or Ephestia kuehniella (Lepidoptera: Pyralidae) eggs. Different densities of prey eggs including 1, 2, 3, 4, 5, 8, 10, 15, 20, 30 and 40 (latest only for E. kuehniella) were used at laboratory conditions. The results showed that both predatory bugs had type II functional response. Also, predation indices were significantly different between the predators. Although N. tenuis was more efficient against T. absoluta eggs than M. pygmaeus, M. pygmaeus predatory indices showed that this predator was more efficient on E. kuehniella eggs. Thus, minimum and maximum attack rate were observed in N. tenuis fed on E. kuehniella (0.0871 h^?1) and T. absoluta (0.2514 h^?1) eggs, respectively. Whilst, the minimum and maximum handling time were observed in M. pygmaeus fed on E. kuehniella (1.8695 h) and T. absoluta (2.7415 h) eggs, respectively.     

Reproductive parameters and life expectancy of Tetranychus urticae (Acari: Tetranychidae) on 12 genotypes of melon and cucumber in laboratory condition

The effect of two host plant species including eight genotypes of melon (Cucumis melo L.) and four genotypes of cucumber (Cucumis sativus L.) was studied on reproductive parameters: life expectancy and mortality of Tetranychus urticae (Koch) at 25?±?1?°C, 60?±?5% rh and a photoperiod of 16L:8D hours. The results indicated that the highest value of the gross fecundity rate of T. urticae was 96.72?±?16.70 (eggs/female) on Mir sultan and the lowest value was 14.33?±?0.88 on Ananasi. The maximum value of gross fertility rate (41.55?±?4.79) was recorded on Sultan, while the minimum value (1.38?±?0.08) was recorded on Ananasi. The net fecundity rate was varied from 0.47?±?0.09 on Ananasi to 23.53?±?3.96 eggs/female on Sultan. The net fertility rate was 12.96?±?2.18 on Sultan and 0.04?±?0.009 on Ananasi, which was the maximum and minimum values, respectively. The range of gross hatch rate on different melon and cucumber genotypes was 9.67% on Ananasi to 72.46% on Super sultan. The cohort reared on Super sultan had the highest mean eggs per day and those on Shah abadi had the lowest mean eggs per day. In addition, the mite demonstrated the maximum value of mean fertile eggs per day with the amount of 1.66?±?0.19 eggs/female when fed on Sultan, and Ananasi demonstrated the minimum value (0.09?±?0.005). The life expectancy of one-day-old adults of T. urticae was estimated to be 16?days on Garmak Isfahan and 26.62 days on Mir sultan which is the maximum and minimum values, respectively. Furthermore, the highest mortality percentage of immature stages of T. urticae was recorded on Ananasi and the lowest was recorded on Super sultan. Comparison of the data collected in this study revealed that the mites had considerably better performance on cucumber genotypes than melon genotypes, so we can assume that cucumber is the preferable host species for T. urticae. The use of preferable and resistant host plants is helpful in crop rotation and it will be one of the beneficial strategies to integrated pest management programmes.     

Pre-release evaluation of absolute spillover impact risk of Physonota maculiventris (Chrysomelidae: Cassidinae) on non-target plant species Helianthus annuus (Asteraceae) and Zea mays (Poaceae) in South Africa

The tortoise beetle, Physonota maculiventris (Coleoptera: Chrysomelidae), a candidate biological control agent of Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae) was screened for spillover risks on non-target plant species in South Africa. Studies were conducted to measure the absolute feeding damage and reproductive performance of P. maculiventris on non-target plant species, Helianthus annuus L. (Asteraceae) and Zea mays L. (Poaceae). The influence of spillover on generational build-up performance on the non-target plant species was also investigated. Adult female beetles were switched from T. diversifolia at 14 (actively feeding colony) or 24 (gravid colony) days to the non-target species. Likewise, as a backup or control, female beetles were exposed to H. annuus in a no-choice situation and switched to T. diversifolia and Z. mays. Feeding damage, adult longevity and egg production of P. maculiventris were significantly lower on H. annuus, compared to those metrics on T. diversifolia. Gravid P. maculiventris adults switched from T. diversifolia on the 14th day after emergence laid a few egg batches on the leaf surfaces of Z. mays, but no signs of feeding were observed. Furthermore, the population of P. maculiventris significantly increased by 11.7 fold (26.8–312.5 adults) between the first (F1) and second (F2) generations on T. diversifolia, while on the non-target, H. annuus, it decreased from 6.3 to zero (0). The study concludes that P. maculiventris will sustain its populations entirely on the target, T. diversifolia population stands associated with or without H. annuus and Z. mays cultivations at different scales in South Africa.     

Influence of target plant density on herbivorous insect oviposition choice: Ambrosia artemisiifolia L. (Asteraceae) and Zygogramma suturalis F. (Coleoptera: Chrysomelidae)

Zygogramma suturalis F. has been introduced to Russia for the biological control of the common ragweed Ambrosia artemisiifolia L. The functional response of Z. suturalis to the density of the target plant was studied at two levels: between plants and between 0.1 m² sampling plots. The number of Z. suturalis eggs per unit of plant weight was almost independent of plant weight, indicating that a functional response between plants is absent. However, tall and intermediate height plants received more eggs per phytomass unit than short plants. Between plots, correlation analysis showed that absolute Z. suturalis egg density is positively dependent on the ragweed density. Experiments showed that the locomotor activity of ovipositing females decreased when on the ragweed, suggesting orthokinesis. The number of leaf beetle eggs per unit of ragweed weight was negatively correlated with host plant density in May‐June, when the majority of eggs are laid, but was positively correlated in July and loosely, or not significantly, correlated in August. Seasonal changes in the functional response of a herbivorous insect to host plant population density have not been reported previously. A negative functional response of a herbivorous insect to target plant density can be a serious obstacle to the biological control of weeds.     

The tortoise beetle Physonota maculiventris (Chrysomelidae: Cassidinae) is suitable for release against the weedy Mexican sunflower Tithonia diversifolia (Asteraceae) in South Africa

The biology and host range of the defoliating beetle Physonota maculiventris Boheman (Chrysomelidae: Cassidinae) were studied in quarantine to determine its suitability for release as a biological control agent against Mexican sunflower, Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae), in South Africa. Females laid 5.25?±?0.25 (mean?±?SE) egg batches during their lifetimes, with each batch consisting of approximately 33 eggs. Larvae were highly gregarious as early instars and both larvae and adults fed voraciously, often defoliating the plants completely. The life cycle of the beetle was completed in 67.5?±?7.5 days under quarantine conditions. Among the 58 test plant species subjected to no-choice tests, P. maculiventris developed successfully on T. diversifolia and some sunflower (Helianthus annuus L.) cultivars. However, only minor damage was recorded on non-target species, notably the exotic weed Xanthium strumarium L. and some H. annuus cultivars. Also, survival to adulthood was considerably lower on sunflower cultivars than on the target weed during these tests. During choice tests, P. maculiventris oviposited and developed successfully on T. diversifolia only, with only minor feeding damage on some H. annuus cultivars, suggesting that the beetle’s field host range will be confined to the target weed. Risk analysis also showed that P. maculiventris presents an extremely low risk to non-target plant species (e.g. within the tribe Heliantheae and other close relatives). The study concluded that P. maculiventris is safe for release in South Africa and an application for its release is being considered by the relevant South African regulatory authorities.     

Functional response of Neoseiulus barkeri Hughes on two-spotted spider mite (Acari: Tetranychidae)

Generalist predatory mites are the common phytoseiid fauna in many agroecosystems, but little attention has been paid to their potential as biological control agents. In this study, we determined the functional responses of adult females of the generalist predator Neoseiulus barkeri Hughes on eggs, larvae, and adults of the two-spotted spider mite, Tetranychus urticae Koch, in the laboratory. Predation experiments were conducted on pepper leaf discs over a 24 h period at 25±1°C, 70–80% RH and 16L:8D photoperiod. Prey densities ranged 5 to 80 eggs, or 5 to 40 larvae, or 1 to 8 female adults of T. urticae per disc. The predation rate of N. barkeri adult females on T. urticae eggs was the same as on its larvae, but the predation rate on adult females was much lower. The role of generalist predatory mites in integrated and biological control of greenhouse pests was discussed.