Evaluation of Natural and Factitious Food Sources for Pronematus ubiquitus on Tomato Plants

Pronematus ubiquitus (McGregor) is a small iolinid mite that is capable of establishing on tomato plants. Once established, this mite has been shown to control both tomato russet mite, Aculops lycopersici (Tryon) (Acari: Eriophyidae), and tomato powdery mildew (Oidium neolycopersici L. Kiss). In the present study, we explored the effects of a number of alternative food sources on the oviposition rate in the laboratory. First, we assessed the reproduction on food sources that P. ubiquitus can encounter on a tomato crop: tomato pollen and powdery mildew, along with tomato leaf and Typha angustifolia L. In a second laboratory experiment, we evaluated the oviposition rate on two prey mites: the astigmatid Carpoglyphus lactis L. (Acari: Carpoglyphidae) and the tarsonemid Tarsonemus fusarii Cooreman (Acari: Tarsonemidae). Powdery mildew and C. lactis did not support reproduction, whereas tomato pollen and T. fusarii did promote egg laying. However, T. angustifolia pollen resulted in a higher oviposition in both experiments. In a greenhouse trial on individual caged tomato plants, we evaluated the impact of pollen supplementation frequency on the establishment of P. ubiquitus. Here, a pollen addition frequency of every other week was required to allow populations of P. ubiquitus to establish.

Fitness Costs of Chlorantraniliprole Resistance Related to the SeNPF Overexpression in the Spodoptera exigua (Lepidoptera: Noctuidae)

Spodopteraexigua, a multifeeding insect pest, has developed a high level of resistance to chlorantraniliprole, which is a benzoylurea insecticide that targets the ryanodine receptors (RyRs). Herein, the resistant strain (SE-Sel) and sensitive strain (SE-Sus) were obtained by bidirectional screening for six generations. The potential oviposited eggs and oviposition rate of the SE-Sel strain were dramatically lower than those of the SE-Sus strain; on the contrary, the weights of prepupae and preadult were significantly increased. As a post-mating response, the higher number of non-oviposited eggs in the SE-Sel strain was caused by a lower mating rate. In addition, the expression levels of vitellogenin (SeVg) and its receptor (SeVgR) in the SE-Sel strain were consistently lower than those in the SE-Sus strain. An RyRI4743M mutation, contributing to the resistance to chlorantraniliprole, was located in the S3 transmembrane segments and might have affected the release of calcium ions; it led to the upregulated expression of the neuropeptide SeNPF and its receptor SeNPFR, and the mating and oviposition rate were significantly recovered when the SeNPF was knocked down though RNA interference (RNAi) in the male adult of the SE-Sel strain. Moreover, the expression of the juvenile hormone-binding proteins SeJHBWDS3 and SeJHBAN in the male adult of the SE-Sel strain was significantly decreased, which proved the existence of a fitness cost from another angle. Therefore, these results indicate that the fitness cost accompanied by chlorantraniliprole resistance in S. exigua may be related to the decrease in mating desire due to SeNPF overexpression.

Sublethal Impacts of Novaluron on Tarnished Plant Bug (Hemiptera: Miridae) Adults

Tarnished plant bug, Lygus lineolaris Palisot de Beauvois (Hemiptera: Miridae), has become a primary pest of cotton in the Midsouthern United States. Insect growth regulators such as novaluron are an important part of L. lineolaris management. While novaluron is lethal to nymphs, it does not kill adults, so it has been used when nymphs are the primary stage present. However, cotton yield protection was observed from an application of novaluron when adults were the predominant stage present. To explain this, a series of studies were conducted to examine sublethal impacts of novaluron to L. lineolaris adults. Novaluron ingestion by adults reduced hatch rate and sometimes reduced oviposition rate. Ingestion by either males or females reduced hatch rates, but the reduction was greater from female exposure. Contact exposure of adults with novaluron residues within 1 d of application reduced hatch rate by about 50%, but the impact on oviposition was inconsistent. A field study showed reduced hatch rate from contact exposure to mixed-age natural populations, but the overall net reproductive rate was not reduced. Surface exposure of eggs to novaluron did not reduce hatch rate. Overall, exposure of tarnished plant bug adults to novaluron, regardless of adult age or exposure route, reduced egg viability. However, the impact on oviposition rate and net reproductive rate varied with adult age and exposure route. This understanding of sublethal impacts of novaluron, in addition to lethal impacts on nymphs, should be considered when choosing application times to maximize effects on L. lineolaris populations.

The effect of con/heterospecific diet on predation, oviposition and longevity of Amblyseius swirskii, Neoseiulus californicus and Phytoseiulus persimilis (Acari: Phytoseiidae)

Intraguild predation (IGP) consists of interacting individuals with context dependent roles that compete for food. Information about the predator trophic interactions i.e. cannibalism or feeding on heterospecific juveniles, is a key to understand the real impact of their combinations when introduced in biological control systems. The hypothesis here, assumed that the pairwise introduction of the female predatory mites, N. californicus (predator) + P. persimilis (heterospecific prey) and vice versa, A. swirskii (predator) + P. persimilis (heterospecific prey) and vice versa could exist in the Tetranychus urticae (main prey) scarcity. Three diets consisted of either conspecific or heterospecific six eggs, four eggs + four larvae and four protonymphs were introduced to the guilds. The predation and oviposition rates and the longevity of each female intraguild predator on detached bean leaf disc was recorded every three hours for 12 consecutive days. Neoseiulus californicus predation rate was estimated to be highest on conspecific eggs + larvae (11.35 ± 1.12) and so was on those of P. persimilis (55.7 ± 3.42). No significant difference was observed in N. californicus oviposition rate on three conspecific diets (P > 0.05), while its oviposition rate was highest on P. persimilis eggs + larvae (7.15 ± 0.80). Phytoseiulus persimilis predation rate was estimated to be highest on eggs + larvae both on N. californicus and P. persimilis as prey. Its oviposition rate was estimated to be highest when feeding on conspecific eggs (2.25 ± 0.19) and N. californicus eggs + larvae. Amblyseius swirskii fed on 45 ± 2.79 P. persimilis and 12.90 ± 1.51 A. swirskii eggs + larvae, which was significantly higher than predation rates on other stages (P < 0.01). Amblyseius swirskii oviposition rate was not significantly different on each of the three diets or on A. swirskii or P. persimilis as prey (P > 0.05). The oviposition rate of P. persimilis was the highest on A. swirskii eggs + larvae (1.45 ± 0.19). When N. californicus fed on each of the three diet types, no significant difference was observed in its longevity. The greatest longevity of P. persimilis was recorded when feeding on N. californicus/P. persimilis eggs. Longevity of A. swirskii was the greatest on P. persimilis eggs and protonymphs. Similarly, P. persimilis had the greatest longevity feeding on A. swirskii eggs. We concluded that the predator species were capable of surviving under conditions of scarce prey when heterospecific species are present.

Predation, prey preference and reproduction of predatory mites Amblydromalus limonicus (Garman), Amblyseius herbicolus (Chant) and Neoseiulus cucumeris (Oudemans) (Mesostigmata: Phytoseiidae) on immature Sericothrips staphylinus Haliday (Thysanoptera: Thripidae), a biocontrol agent of gorse

Gorse, Ulex europaeus, is an invasive weed that has serious agricultural, economic and ecological impacts. Although various biological control agents have been released in New Zealand, these have showed no noticeable impact on gorse populations. One such agent, Sericothrips staphylinus, was introduced to New Zealand in 1990 and although laboratory impact studies indicated it was a highly promising gorse biological control agent, it has not been as effective as was hoped. We hypothesized this was due to predation by natural enemies. This study investigated the predation and oviposition rates of three phytoseiid mites (Amblydromalus limonicus, Amblyseius herbicolus, and Neoseiulus cucumeris) that have been found on gorse plants in New Zealand on three S. staphylinus stages (1st instar larvae, 2nd instar larvae, and prepupa) in both choice and non-choice conditions. In non-choice conditions, A. limonicus had the highest predation and oviposition rate across all three immature stages, and N. cucumeris had the lowest. Amblydromalus limonicus, A. herbicolus, and N. cucumeris all had their highest predation rate when consuming 1st instar larvae, and their lowest predation rate when consuming prepupa. In the choice experiment, all three predatory mite species consumed their highest proportion of 1st instar larvae, and their lowest proportion of prepupae. The oviposition rate of all three mite species in the choice experiment was similar to the oviposition rate when presented with 1st instar larvae only. The results from this study confirm that A. limonicus, A. herbicolus, and N. cucumeris can predate and reproduce on S. staphylinus 1st instar larvae, 2nd instar larvae, and prepupa. This indicates that predation may be the reason why S. staphylinus is an ineffective biocontrol agent in New Zealand.

Methods for quantifying eggs and oviposition rate of Dawestrema cycloancistrium (Monogenea: Dactylogyridae), monogenean parasite of Arapaima gigas (Teleostei: Osteoglossidae)

Dawestrema cycloancistrium is the main ectoparasite causing mortality in fingerlings of pirarucu (Arapaima gigas) in Amazonian aquaculture. Very little is known about the D. cycloancistrium reproductive index and appropriate methods of collecting eggs for investigation. This study aimed to determine the oviposition rate of D. cycloancistrium. To achieve this aim, two egg quantification methods were tested: the estimative method (ME) and the total counting method (MT). Compared with the MT, the ME overestimated the number of eggs counted, which were 2943.5 ± 2840.6 and 1041.5 ± 533 eggs, and the oviposition rate, which was 80.1 ± 58.7 and 31.4 ± 16.4 eggs/parasite/day, for ME and MT, respectively. These results show that for studies quantifying D. cycloancistrium eggs, the total eggs in the sample must be counted, as the estimates made using subsamples are not representative. Using the MT, the oviposition rate for D. cycloancistrium was determined to be 31.4 ± 16.4 eggs per adult parasite per day. The present study demonstrates the egg production capacity of a monogenean species parasite of A. gigas, providing basic biological data for D. cycloancistrium.