Dionyssios Ch. Perdikis

Life table and biological characteristics of Macrolophus pygmaeus when feeding on Myzus persicae and Trialeurodes vaporariorum

The life table and biological characteristics of the predatory bug Macrolophus pygmaeus Rambur (Hemiptera: Miridae) were studied when the bugs were fed with Myzus persicae (Sulzer) (Homoptera: Aphididae) feeding on eggplant and with Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) feeding on tomato plants. The tests were done at five temperatures between 15 and 30 °C, using a L16:D8 photoperiod and 65 ± 5% r.h. Most eggs (range 85 to 90%) hatched at 15 and 20 °C. Incubation period was shortest at 27.5 °C (8.45 and 8.38 days on eggplant and tomato, respectively). Preoviposition was also shortest at 27.5 °C (5.10 and 4.75 days on eggplant and tomato, respectively) whereas fecundity was highest at 20 °C (213.90 and 228.25 eggs on eggplant and tomato, respectively). Maximum longevity of females was at 15 °C (122.40 and 129.35 days on eggplant and tomato, respectively). Mean generation time was longest at 15 °C on both host plants (122.75 and 124.64 days, respectively). The intrinsic rate of increase of M. pygmaeus was highest at 27.5 °C with similar values on eggplant (0.0981 day−1) and tomato (0.1040 day−1). Doubling time was shortest at 27.5 °C (7.06 and 6.67 days on eggplant and tomato, respectively) and, also, finite rate of increase was highest at 27.5 °C (1.1031 and 1.1096 on eggplant and tomato, respectively). The results show that the predator M. pygmaeus develops well on the aphid M. persicae or on the whitefly T. vaporariorum, both of which are important pests of vegetable crops. This predator is also well adapted to the temperatures that occur both in greenhouses and in the open field in the Mediterranean region. Compared to other natural enemies of whiteflies, such as Encarsia formosa Gahan (Hymenoptera: Aphelinidae), Macrolophus pygmaeus can increase at relatively low temperatures.

Development of Immature Stages of Sesamia nonagrioides (Lepidoptera : Noctuidae) Under Alternating and Constant Temperatures

Abstract Laboratory studies on the temperature-dependent development of Sesamia nonagrioides (Lefebvre) were performed under five constant temperatures ranging from 20 to 30°C as well as under the corresponding alternating temperatures of 25:10, 27.5:12.5, 30:15, 32.5:17.5, and 35:20°C, at a photoperiod of 16:8 (L:D) h. Both linear and nonlinear (Lactin formula) models provided a reliable fit of developmental rates versus temperature for all immature stages either at constant or alternating temperatures. Developmental thresholds that were estimated by a linear model for eggs, larvae, or pupae were approximately the same and estimated to be 10.57, 8.89, and 10.75°C, respectively, at constant temperatures. Lower values were estimated when immature stages were exposed to the corresponding alternating temperatures (7.23, 6.20, and 6.50°C for eggs, larvae, and pupae). Therefore, the evaluation of the development of immature stages under constant temperatures resulted in an overestimation of the lower thresholds. The Lactin-2 model also was applied, and larval and egg developmental thresholds did not differ from those that were estimated by the linear model. Differences, however, occurred at the pupal stage. Nevertheless, the differences in the estimated values of the lower developmental thresholds of the immature stages under constant or alternating temperatures indicate that a model predicting phenology in the field should be based on fluctuating temperature.

Thermal Requirements for Development of the Polyphagous Predator Macrolophus pygmaeus (Hemiptera: Miridae)

Abstract The effect of temperature on the duration of embryonic and nymphal development as well as on the preoviposition period of the polyphagous predator Macrolophus pygmaeus Rambur was studied in the presence and in the absence of prey on eggplant, pepper-plant, and tomato at 15, 20, 25, 27.5, 30, and 35°C, with 65 ± 5% RH and photoperiod of 16:8 (L:D) h. The aphid Myzus persicae (Sulzer) was used as prey on eggplant and pepper-plant and the whitefly Trialeurodes vaporariorum (Westwood) on tomato. The data obtained were used for the estimation of the thermal requirements of this predator. The temperature threshold for egg development was found as 7.61 and 6.92°C, for nymphal development in the presence 8.74 and 9.19°C and in the absence of prey 8.21 and 9.29°C, for preimaginal development 8.68 and 8.79°C, for preoviposition 7.58 and 6.96°C, and finally for egg-to-egg development 8.48 and 8.51°C on eggplant with M. persicae and on tomato with T. vaporariorum, respectively. On pepper-plant the temperature threshold for nymphal development was 8.26 and 8.23°C in the presence and in the absence of prey, respectively. The values of temperature threshold for development of the various nymphal stages were similar. It was also found that the slopes of the linear regressions between the rate of nymphal development and temperature were not significantly different among the different host plants in the presence and in the absence of prey. Also, the slopes of the linear regressions concerning the development of each nymphal stage with temperature were not found to differ significantly among the host plants in the presence and in the absence of prey. The thermal constant for egg development was estimated as 177 and 182, that for nymphal development in the presence 269 and 253 and in the absence of prey 332 and 306, for preimaginal development 439 and 431, for preoviposition 100 and 98 and finally that of egg-to-egg development 541 and 533 degree-days when fed on M. persicae on eggplant and on T. vaporariorum on tomato, respectively. On pepper-plant the degree-days for nymphal development was 280 and 361, in the presence and in the absence of prey, respectively. The temperature threshold for development was not found to differ among the host plants in the presence and in the absence of prey. However, the degree-days were significantly different between the presence and absence of prey on each host plant; the thermal constant in the absence of prey was estimated as an average of 1.21 times of that in the presence of prey. The results show that M. pygmaeus can establish, develop, and oviposit even in the absence of prey in relatively low temperatures and hence it can be released early in the season for an earlier and more effective control of whiteflies and aphids on vegetables.

Biological characteristics of the mirids Macrolophus costalis and Macrolophus pygmaeus preying on the tobacco form of Myzus persicae (Hemiptera: Aphididae).

Biological and population parameters of the predatory bugs Macrolophus costalis Fieber and Macrolophus pygmaeus Rambur preying on the tobacco aphid Myzus persicae (Sulzer) were examined. Tobacco was used as host plant and all experiments were carried out at 23 degrees C and L16:D8. In M. costalis, the developmental time for eggs and the total duration of nymphal instars was 13.1 and 22.2 days and in M. pygmaeus 13.0 and 20.2 days, respectively. Both species completed their nymphal development feeding only on plant juices although they required significantly more time to attain adulthood than when feeding on prey. The longevity of M. costalis females and the preoviposition period were 49.9 and 5.6 days and those of M. pygmaeus were 50.3 and 6.3 days, respectively. Adult males showed a higher longevity than females in both species. The intrinsic rate of increase and the mean total number of eggs laid were 0.0644 and 121 in M. costalis and 0.0615 and 104 in M. pygmaeus, respectively. Mean total aphid consumption by nymphs of M. costalis was 61 aphids, about twice that of M. pygmaeus (37 aphids). Total aphid consumption by a male and female pair of M. costalis and M. pygmaeus until the death of the female was 244 and 285 aphids, respectively. The results of the study are discussed in relation to the impact of the two predatory bugs on tobacco aphid populations.

Discrimination of the closely related biocontrol agents Macrolophus melanotoma (Hemiptera: Miridae) and M. pygmaeus using mitochondrial DNA analysis

The separation of the closely related predatory species Macrolophus melanotoma Costa (= M. caliginosus Wagner) and Macrolophus pygmaeus (Rambur) based exclusively on the different colour pattern of the first antennal segment (white central band in M. melanotoma and entirely black in M. pygmaeus) is rather precarious and their taxonomic status is still in doubt. In the present study their taxonomic status was evaluated by DNA confirmatory analysis and hybridization experiments between M. pygmaeus and a Macrolophus taxon, resembling M. melanotoma, with a first antennal segment entirely black or with a white central band collected from Dittrichia viscosa (L.) W. Greuter (Asteraceae) in southern Greece. Adult females from Dittrichia plants hybridized with males of M. pygmaeus and vice versa did not produce viable eggs. The Macrolophus species from Dittrichia irrespective of the first antennal segment coloration differed from M. pygmaeusin digestive patterns generated by AseI, XbaI, and MseI on 16S rRNA and in RAPD profiles produced by the primers OPA-18 and OPA-20. These results demonstrate that on Dittrichia plants there is a distinct dimorphic taxon, M. melanotoma, as it is the only species of the genus Macrolophus bearing a first antennal segment with a central white band. Given the limitation of the coloration pattern, the mtDNA genetic markers are the appropriate method for the identification of M. melanotomaand M. pygmaeus.

Myzus persicae (Homoptera: Aphididae) as Suitable Prey for Macrolophus pygmaeus (Hemiptera: Miridae) Population Increase on Pepper Plants

Abstract Life table parameters and other biological characteristics were estimated for the predator Macrolophus pygmaeus Rambur (Hemiptera: Miridae) when fed on pepper plant/leaves with or without prey Myzus persicae (Sulzer) (Homoptera: Aphididae). The experiments were conducted at 15, 20, 25, and 30°C, under a photoperiod of 16:8 (L:D) h and at 65 ± 5% RH. Egg incubation was shortest at 30°C (10.5 d), egg hatch percentage reached 90% at 20°C, sex ratio was 78% at 25°C, and preoviposition period was shortest at 25°C (6.1 d). Only females with access to prey were able to reproduce. Fecundity was highest at 20°C (203.9 eggs). Females and males survived longer at 15°C (120.7 and 132.9 d, respectively). When provided with prey, M. pygmaeus can increase its numbers at all temperatures tested. Its intrinsic rate of increase and doubling time were highest at 25°C (0.0958 d−1 and 7.2 d, respectively). The lowest temperature threshold for population increase was 9.06°C. In the absence of prey, the predator did not oviposit, but females and males survived for a relatively long time at 15°C (26.5 and 28.7 d, respectively) and for a shorter time as temperature increased. The results indicate that M. pygmaeus performs very well when it feeds on the aphid M. persicae on pepper plants. Although the pepper plant can support adults, it does not permit population increase when prey is not available. However, these results are discussed with other findings in the context of a better and more effective use of this predator for biological control of M. persicae on pepper plant.

Reproductive responses to photoperiod and temperature by diapausing and nondiapausing populations of Sesamia nonagrioides Lef. (Lepidoptera − Noctuidae)

Abstract.  The influence of long‐ and short‐day cycles on ovipostion and egg hatch of the corn stalk borer, Sesamia nonagrioides were investigated at a range of temperatures. Oviposition was suppressed when insects are exposed to long days through their immature stages and then transferred to short days after mating. Moreover, mean oviposition and egg hatch increased from 15 to 27.5 °C, whereas oviposition declined significantly at 30 °C at both photoperiodic regimes. Females derived from a diapausing population exposed to long days after mating showed a significantly higher egg production compared to females derived from a nondiapausing population. However, when females from a diapausing population were left to oviposit under short days, fewer eggs were produced compared to those exposed to long days after mating. Thus, photoperiod appears to affect reproductive traits of this species in a quantitative manner. Larval diapause duration is positively correlated with fecundity of the adults. There is also a positive correlation between pupal weight of individuals derived from a diapausing population and the postdiapause fecundity of adults.

Nettle extract effects on the aphid Myzus persicae and its natural enemy, the predator Macrolophus pygmaeus (Hem., Miridae)

Abstract:  The effect of water extract of Urtica urens L. on the biological characteristics and population parameters of Myzus persicae (Sulzer) and its natural enemy, the polyphagous predator Macrolophus pygmaeus (Rambur) was investigated on eggplants. Plant material was extracted in deionized water (1 : 5 w/w) for 24 h. Three applications were made at 5‐day intervals using the nettle extract, with deionized water as the control. The effect of the extract on survival, duration of nymphal development, pre‐reproductive period, fecundity and longevity of both insects was studied at conditions of 25 ± 1°C, 65 ± 5% relative humidity and photoperiod of 16 : 8 h (light : dark). The results showed that the application of nettle extract significantly reduced the fecundity of M. persicae (20% on average) but did not result in a substantial lowering in its intrinsic rate of population increase. However, the predators biological characteristics and population parameters were not affected by the application of this plant extract. The importance of these results for the use of nettle extract in the management of M. persicae along with its compatibility with the use or conservation of M. pygmaeus is discussed.

A Method for Laboratory Studies on the Polyphagous Predator Macrolophus pygmaeus (Hemiptera: Miridae)

Abstract A method for studying the life history parameters of Macrolophus pygmaeus Rambur was developed and described. Fecundity of the predator was studied by placing one female and one male in a plastic cylinder in which a stem piece was used as an ovipositional substrate. Smaller cylinders were used to study the percentage of egg hatch of M. pygmaeus. Results demonstrated that this method is suitable for studying the fecundity and egg eclosion of M. pygmaeus. Allowing for easy modification, the method offers suitable conditions for maintenance of both insect and plant material and can be inexpensively modified for different experiments and the parts are easily constructed. The proposed method could also be employed for similar studies on other predatory hemipterans such as mirids and anthocorids and very likely on other phytophagous insect species that lay their eggs in or on plant stems.

Plant food effects on prey consumption by the omnivorous predator Macrolophus pygmaeus

Omnivorous predatory Heteroptera are important biological control agents of pests in several crops. They can feed on plant food resources that may positively affect their biological characteristics. In the current paper, the influence of leaves and flowers on the predation rate of the omnivorous predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) was investigated. Its predation rates were recorded on prey offered on (a) a single leaf of tomato, pepper or black nightshade (Solanum nigrum), or (b) a leaf of pepper or S. nigrum plus flowers of pepper or S. nigrum, respectively. In all cases the aphid Myzus persicae (Sulzer) (Homoptera: Aphididae) was used as prey at densities of 4, 8, 12, 16, 20 and 24 nymphs of the second instar. The experiments were conducted in petri dishes at 25 ± 1°C and prey consumption was evaluated after 24 h. The predation rate of M. pygmaeus was significantly higher on leaves of S. nigrum than on those of pepper at the prey density of 20 prey items. Therefore, the hypothesis that increased predation rates should occur on plants of lower suitability for development or reproduction was not supported under our experimental conditions. The flower availability did not alter the prey consumption among the prey densities on S. nigrum. However, the presence of a pepper flower caused a significant decrease in the predation rates on pepper leaves, at prey densities higher than eight prey items. Thus, pepper flowers can provide the predator with nutrient sources that may partially substitute for prey consumption, with practical implications in biological control.