Implications of using two natural enemies of Tuta absoluta (Lepidoptera: Gelechiidae) toward tomato yield enhancement.

Tomato leaf miner (TLM), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the most destructive tomato pests worldwide. We tested quantity and quality of tomato fruits after simultaneous use of two biological control agents, the predatory mirid bug Nesidiocoris tenuis (Reuter) and the egg parasitoid Trichogramma brassicae Bezdenko against TLM. We varied the timing of predator releases (before or after pest establishment) and the number of parasitoids released (ten or 30 females per week per m2). The highest number of fruits per cage, percentage of undamaged fruits, total yield weight, and undamaged yield weight were all obtained with predator-in-first treatments, with or without parasitoid releases. Furthermore, measures of fruit quality were also highest in predator-in-first treatments, including, highest percentage of water, greatest proportional fresh weight of carbohydrates, most lycopene, most ß-carotene, most flavonoids, and highest total chlorophyll. Thus, our findings support a predator-in-first augmentation approach for management of TLM.

Gamma irradiation on canola seeds affects herbivore-plant and host-parasitoid interactions.

As an agricultural modernization, gamma irradiation is an important method for enhancing crop yield and quality. Nevertheless, its use can alter other plant traits such as nutrition and resistance to different biotic/abiotic stresses that consequently affect plant-insect interactions. A tritrophic system was utilized based on two canola mutant lines produced through gamma irradiation (RGS 8-1 and Talaye 8-3). Plutella xylostella (L.), as a worldwide pest of Brassicaceae and Cotesia vestalis (Holiday) as a key biocontrol agent of P. xylostella were examined for the potential indirect effects of canola seed irradiation on the experimental insects' performance when acting on the respective mutant lines. This study showed that physical mutation did not affect plant nitrogen and herbivore-damaged total phenolics; however, phenolic compounds showed greater concentration in damaged leaves than undamaged leaves of both mutant and control plants. The relative growth rate and pupal weight of P. xylostella reared on RGS 8-1 were significantly higher than those reared on the control RGS. There was no significant difference by performance parameters of the parasitoid, C. vestalis, including total pre-oviposition period, adult longevity, adult fresh body weight of males and females, pupal weight, forewing area, and total longevity of both sexes on tested canola cultivars in comparison with their mutant lines. Life table parameters of C. vestalis on mutant lines of both cultivars, RGS and Talaye, were not significantly different from their control treatments. Comprehensive studies should be conducted to find out the mechanisms under which gamma rays affect plant-insect interactions.

Age-Specific Functional Response of Aphidius matricariae and Praon volucre (Hymenoptera: Braconidae) on Myzus persicae (Hemiptera: Aphididae).

The green peach aphid, Myzus persicae (Sulzer), is one of the most important aphid pests on pepper. Aphidius matricariae Haliday and Praon volucre (Haliday) are known as biological control agents for aphids in vegetable crops. In this research, age-specific functional responses of these two parasitoids were evaluated on different densities of 2, 4, 8, 16, 32, and 64 green peach aphids. Type of functional response varied from type II to type III for different ages of A. matricariae, but type of functional response was not affected by female age for P. volucre. The functional response of P. volucre was determined as type II in the whole parasitoid lifetime. The searching efficiency (a), b, and handling time (T h ) were estimated using the Rogers equations. The highest searching efficiency (a) and lowest handling time were observed during the first half of lifetime of A. matricariae and P. volucre. Aphidius matricariae and P. volucre caused reasonable mortality of the green peach aphid by parasitism of 52.17 and 47.05 host aphids, respectively, in 24 h. Therefore, they are suggested as suitable candidates for control of M. persicae in pepper greenhouses.

Effects of plant availability on population size and dynamics of an insect community: diamondback moth and two of its parasitoids.

To understand the effect of plant availability/structure on the population size and dynamics of insects, a specialist herbivore in the presence of two of its parasitoids was studied in four replicated time-series experiments with high and low plant availabilities; under the latter condition, the herbivore suffered from some periods of resource limitation (starvation) and little plant-related structural refuges. Population dynamics of the parasitoid Cotesia vestalis was governed mainly by the delayed density-dependent process under both plant setups. The parasitoid, Diadegma semiclausum, under different plant availabilities and different coexistence situations (either +competitor or -competitor) showed dynamics patterns that were governed mainly by the delayed density process (significant lags at weeks 2-4). Both the competing parasitoids did not experience beneficial or costly interferences from each other in terms of their own population size when the plant resource was limited. Variation in the Plutella xylostella population under limited plant availability is higher than that under the other plant setup. For both parasitoids, under limited plant setup, the extinction risk was lower when parasitoids were engaged in competition, while under the unlimited plant setup, the mentioned risk was higher when parasitoids competed. In this situation, parasitoids suffered from two forces, competition and higher escaped hosts.