Herbivore-Induced Rice Volatiles Attract and Affect the Predation Ability of the Wolf Spiders, Pirata subpiraticus and Pardosa pseudoannulata

Spiders are important natural enemies of rice pests. Studying the effects of herbivore-induced rice volatiles on spider attraction and predation ability may lead to safer methods for pest prevention and control. In this study, four-arm olfactometer, predation ability experiment, and field trapping experiment were used to evaluate the effects of herbivore-induced rice volatiles on Pirata subpiraticus Bösenberg et Strand (Araneae: Lycosidae) and Pardosa pseudoannulata Bösenberg et Strand (Araneae: Lycosidae). The 0.5 μg/μL linalool concentration was attractive, and also shortened the predation latency in male P. subpiraticus and female P. pseudoannulata. The 0.5 μg/μL linalool concentration increased the daily predation capacity of female P. pseudoannulata. Male P. pseudoannulata were attracted to 1.0 g/L methyl salicylate, which also shortened their predation latency. In field experiments, methyl salicylate and linalool were effective for trapping spiders. Herbivore-induced rice volatiles attract rice field spiders and affect their predatory ability. These results suggest that herbivore-induced rice volatiles can be used to attract spiders and provide improved control of rice pests.

Suitability of pollen as an alternative food source for different developmental stages of Amblyseius herbicolus (Chant) (Acari: Phytoseiidae) to facilitate predation on whitefly eggs

Alternative food sources could sustain predator populations by influencing their performances including predation, development, and reproduction in periods of shortage or scarcity of prey under laboratory or fields conditions. The aim of this study was to explore suitability of cattail pollen (Typha orientalis) as an alternative food source for different stages of Amblyseius herbicolus (Chant) (Acari: Phytoseiidae) on their predation capacity against the eggs of whitefly Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae), and the developmental and reproductive responses of the predators to different diet switching regimes under laboratory conditions (T1: nymphs and early adults fed pollen; T2: nymphs fed pollen but early adults fed whitefly eggs; T3: nymphs fed whitefly eggs but early adults fed pollen; T4: nymphs and early adults fed whitefly eggs). Results in the diet switching experiment revealed that although A. herbicolus could prey on whitefly eggs in all the treatment groups, the predatory mites obviously differed in their capacity to prey on the target pest whitefly eggs when fed on cattail pollen and whitefly eggs during different developmental stages. A. herbicolus in group T2 revealed the highest average predation rate, being 1.31, 1.17, and 1.49 times those in groups T1, T3, and T4, respectively. Our results indicated that food sources including cattail pollen and whitefly eggs were suitable for A. herbicolus, because it was able to develop from egg to adult females in all the treatment groups. The mixed diets (T2 and T3 groups) revealed positive effects on the developmental and reproductive parameters of A. herbicolus females, leading to higher oviposition rates and shorter developmental durations when compared with those of groups T1 and T4. A. herbicolus in group T2 revealed the highest average oviposition rates (1.32, 1.26, and 1.81 times those in groups T1, T3 and T4, respectively); however, no significant differences were observed between the T1 and T3 groups. All the eggs of A. herbicolus succeeded in reaching adulthood, but the duration of egg to adult developmental time of A. herbicolus was different among the four treatment groups. The longest and shortest developmental times were obtained in groups T4 and T3, respectively. All the results in the present study demonstrated that A. herbicolus adult females can prey on T. vaporariorum eggs, and cattail pollen was suitable as an alternative or additional food source with high nutritional value for this predatory mite to enhance the predation capacity towards whitefly eggs because A. herbicolus can successfully complete its immature development as well as reproduction.

Predation capacity of soil-dwelling predatory mites on two major maize pests

The western corn rootworm Diabrotica virgifera virgifera (WCR), and the wireworm Agriotes sordidus (WW), whose eggs and first instar larvae develop in the first few centimeters of soil, are major crop pests. As soil-dwelling predatory mites are known as potential biocontrol agents against many pests, we investigated the predation capacity of Stratiolaelaps scimitus, Gaeolaelaps aculeifer and Macrocheles robustulus on immature stages of WCR and WW in a laboratory setting. While eggs of WCR and WW were never consumed, all three predator species attacked both WCR and WW first instar larvae. While these results need to be confirmed in natural conditions, our work identifies the early larval stage instead of the egg stage as the most vulnerable stage for control against WCR and WW with soil-dwelling predatory mites.

Functional Response and Predation Rate of Dicyphus cerastii Wagner (Hemiptera: Miridae)

Dicyphine mirids are important biological control agents (BCAs) in horticultural crops. Dicyphus cerastii Wagner can be found in protected tomato crops in Portugal, and has been observed feeding on several tomato pests. However, the predation capacity of this species is poorly studied. In order to investigate the predation capacity of D. cerastii, and how it is affected by prey size and mobility, we evaluated the functional response (FR) and predation rate of female predators on different densities of four prey species: Myzus persicae 1st instar nymphs (large mobile prey), Bemisia tabaci 4th instar nymphs, Ephestia kuehniella eggs (large immobile prey) and Tuta absoluta eggs (small immobile prey). Experiments were performed on tomato leaflets in Petri dish arenas for 24 h. Dicyphus cerastii exhibited type II FR for all prey tested. The predator effectively preyed upon all prey, consuming an average of 88.8 B. tabaci nymphs, 134.4 E. kuehniella eggs, 37.3 M. persicae nymphs and 172.3 T. absoluta eggs. Differences in the FR parameters, attack rate and handling time, suggested that prey size and mobility affected predation capacity. Considering the very high predation rates found for all prey species, D. cerastii proved to be an interesting candidate BCA for tomato crops.

Studies Aimed at Evaluating the Impact of Generalist Predators on the Leafhopper Erasmoneura vulnerata Populations

Outbreaks of the Nearctic leafhopper Erasmoneura vulnerata represent a recent issue for winegrowers in Southern Europe, in particular in North-eastern Italy. Problems are frequent in organic vineyards because insecticides labeled for organic viticulture show limited effectiveness towards leafhoppers. On the other hand, the response by naturally occurring predators and parasitoids to E. vulnerata populations in vineyards is often unable to keep leafhopper densities under levels that are acceptable for winegrowers. Here we evaluated the potential of two generalist predators, i.e., Chrysoperla carnea and Orius majusculus, in controlling E. vulnerata populations. Laboratory and semi-field experiments were carried out to evaluate both species' predation capacity on E. vulnerata nymphs. Then, predators were released in vineyards colonized by large E. vulnerata populations. Both predator species exhibited a remarkable voracity in the laboratory and significantly reduced leafhopper densities in semi-field experiments. Predator releases in vineyards reduced leafhopper densities by about 30%. Results obtained in laboratory, semi-field, and field experiments are discussed to implement these biocontrol agents' use in pest control tactics.

Age-Dependent Functional and Numerical Responses of Neoseiulus cucumeris (Acari: Phytoseiidae) on Two-Spotted Spider Mite (Acari: Tetranychidae)

The age-specific functional and numerical responses of Neoseiulus cucumeris Oudemans (Mesostigmata: Phytoseiidae) on eggs of the two-spotted spider mite, Tetranychus urticae Koch (Prostigmata: Tetranychidae), were assessed in the laboratory using bean leaf discs. Densities of 2, 4, 8, 16, 32, 64, and 128 prey were provided to 4- (protonymph), 6- (deutonymph), 8-, 13-, 18-, 23-, 28-, 33-, and 40-d-old N. cucumeris individuals. The functional response of 28- and 40-d-old N. cucumeris fitted type II, whereas the other ages displayed a type III functional response. The longest handling time observed at the age of 4 d was 0.515 h, whereas the shortest handling time and highest value of maximum attack rate (T/Th) were associated with the age of the 28-d-old treatment (0.261 h and 91.95 prey/d, respectively). The numerical response of N. cucumeris showed a significant increase with increasing prey density, but its rate gradually decreased at higher densities. Therefore, the efficiency of conversion of ingested food was relatively higher at low two-spotted spider mite densities, whereas it was reduced at high two-spotted spider mite densities. The stronger functional response and predation capacity of N. cucumeris on two-spotted spider mite eggs indicated the high potential of this predatory mite as an effective biological control agent against two-spotted spider mite especially at its early and middle ages and also when higher prey densities are present.