Intraguild predation by the generalist predator Dicyphus hesperus on the parasitoid Encarsia formosa

Predation was measured in the laboratory by Dicyphus hesperus females on patches of greenhouse whitefly (Trialeurodes vaporariorum) pupae. The patches contained different proportions of unparasitized pupae and those parastisized as nymphs by Encarsia formosa. Dicyphus hesperus fed readily on parasitized pupae and the number of parasitized pupae consumed increased with the proportion available indicating a capacity for intraguild predation. However, D. hesperus females did not display a preference for feeding on parasitized pupae versus unparasitized pupae. Dicyphus hesperus adults were released at three densities into greenhouse enclosures containing tomato plants harbouring greenhouse whitefly and immature E. formosa. Numbers of killed and parasitized whitefly nymphs and pupae and the total number of healthy whitefly were compared among Dicyphus density treatments. On upper leaves, the amount of predation on whitefly nymphs was higher at the highest predator density than at the lower density or in enclosures where D. hesperus was not released. On lower leaves, the number of parasitized pupae was lowest with the highest predator density indicating a negative effect of intraguild predation by D. hesperus on E. formosa. Despite this, Dicyphus density did not affect the density of whitefly in the presence of E. formosa. The results are discussed as they relate to concurrent use of D. hesperus and E. formosa for regulation of greenhouse whitefly populations.     

Stage-dependent feeding behavior by western tarnished plant bugs influences flower bud abscission in cotton

Unexplained variability in the relationship between the number of herbivores in a field and the amount of crop damage can arise if there is a large amount of variation among herbivore individuals in the amount of feeding damage each generates. In California, populations of the western tarnished plant bug, Lygus hesperus Knight (Heteroptera: Miridae), produce highly variable levels of damage to cotton plants (Gossypium hirsutum L.) (Malvaceae), even when found at low densities. Because L. hesperus populations are also highly variable in their overall stage structure, we hypothesize that differences in crop damage might result from varying impact by each L. hesperus stage on cotton flower buds (termed squares). Laboratory measurements of L. hesperus mouth‐parts and distance to anther sacs, a preferred feeding site, revealed that 1st?3rd instar L. hesperus nymphs will not be able to feed on anther sacs of larger squares (over 8 mm in length) but will be able to feed on squares that are most sensitive to L. hesperus damage (<7 mm). Because even the 1st instars can feed on the most sensitive ‘pinhead’ squares, size constraints do not rule out damaging effects from the youngest L. hesperus. Laboratory observations revealed that later developmental stages, and adults, spend more time feeding on cotton squares relative to 2nd and 3rd instars. In addition, a field experiment revealed no effect of 2nd instars on square retention (relative to control cages) but did reveal a significant decrease in square retention generated by adult L. hesperus (4th instar L. hesperus resulted in an intermediate level of square retention). In a final study we sampled L. hesperus stage structure and density across 38 cotton fields. Multiple regression revealed that the densities of 1st?3rd instars of L. hesperus are not correlated with anther sac damage or square retention. However, in 2 years 4th and 5th instars were positively correlated with anther sac damage and negatively correlated with square retention. In the a third year, adult L. hesperus showed correlations in the same direction, across fields and across sites within fields. Overall, these results suggest that the adults and the largest nymphs of L. hesperus (4th and 5th instars) are particularly damaging to cotton squares, with the 1st?3rd instars of L. hesperus causing little damage to plants.     

Compatibility of an entomopathogenic fungus with a predator and a parasitoid in the biological control of greenhouse whitefly

An ongoing debate in biological control consists of whether interference between biological agents can disrupt pest control. This study investigated the outcome of interactions between the entomopathogen Beauveria bassiana with the whitefly predator Dicyphus hesperus and the parasitoid Encarsia formosa, as well as their effect on the control of the greenhouse whitefly Trialeurodes vaporariorum on greenhouse tomato crops. Our objective was to determine whether the generalist B. bassiana would disrupt biological control by interfering with D. hesperus or E. formosa. In experimental greenhouses, whitefly, parasitoid and predator populations were established, and over 27 days, tomato plants were sprayed with three applications of the B. bassiana based product BotaniGard® (5.13×10³ conidia/mm²) or water (control). Populations of greenhouse whitefly and biological control organisms were regularly monitored in control and B. bassiana-treated compartments. Overall, 10.6% of all whiteflies in treated compartments were infected, and 0.98% were both infected and parasitized. There were 31.7 and 22.3% fewer immature and adult whiteflies, respectively, on B. bassiana-treated plants relative to controls. Parasitism by E. formosa and predation by D. hesperus occurred at rates of 7.5 and 2.5%, respectively, in B. bassiana-treated compartments, and 5 and 6%, respectively in control compartments. Our study suggests that applications of B. bassiana for short-term biological control of greenhouse whiteflies are compatible with the concurrent use of E. formosa and D. hesperus on greenhouse tomato crops.     

Identification of endo- and exo-polygalacturonase activity in Lygus hesperus (Knight) salivary glands

Polygalacturonase (PG) activity found in the salivary gland apparatus of the western tarnished plant bug (WTPB, Lygus hesperus Knight) has been thought to be the main chemical cause of the damage inflicted by this mirid when feeding on its plant hosts. Early viscosity and thermal stability studies of the PG activity in L. hesperus protein extracts were difficult to interpret. Thus, it has been suggested that one or more PG protein(s) with different hydrolytic modes of action are produced by this mirid. In order to understand the quantitative complexity of the WTPB salivary PG activity, PG purification from a protein extract from salivary glands excised from L. hesperus insects was performed using affinity and ion exchange chromatography. To elucidate the qualitative complexity of the purified PGs, the digestion products generated by the PGs were separated using high performance anion exchange chromatography with pulsed amperometric detection. At least five PG proteins were detected; these differing in terms of their glycosylation, mass-to-charge ratios, and/or molecular mass. The characterization of the products generated by these PGs showed that endo- and exo-acting PGs are produced by WTPB. Although none of the PGs was purified to homogeneity, the present work provides biochemical evidence of a multiplicity of PGs that degrade the pectin component of the plant tissue in different fashions. The implications of these findings affect the understanding of WTPB feeding damage and, potentially, help identify ways to control this important crop pest. Arch. Insect Biochem. Physiol. 2008. © 2008 Wiley-Liss, Inc.     

Prey selection by Dicyphus hesperus of infected or parasitized greenhouse whitefly

The development of effective biological control programs in which predators are integrated with other natural enemies such as parasitoids and entomopathogens requires an understanding of their interactions. In this study we examined the extent to which the omnivorous mirid bug Dicyphus hesperus, an effective biological control agent of greenhouse whiteflies, accepts prey that are either parasitized by the specialist whitefly parasitoid, Encarsia formosa or infected by the generalist fungal entomopathogen, Beauveria bassiana. In non-choice laboratory experiments, we measured how parasitism and infection of greenhouse whitefly, Trialeurodes vaporariorum, as related to parasitoid age and course of fungal infection, might alter the probability of feeding by second instar or adult female predators. Predation by D. hesperus was similar for parasitized and unparasitized whiteflies, regardless of parasitoid age. However, predators generally avoided feeding on infected whiteflies, particularly when infection was manifested through the presence of oosporein or hyphae on the surface of prey.     

Evaluation of mirid predatory bugs and release strategy for aphid control in sweet pepper

Zoophytophagous predators of the family Miridae (Heteroptera), which feed both on plant and prey, often maintain a close relationship with certain host plants. In this study, we aimed to select a suitable mirid predatory bug for aphid control in sweet pepper. Four species were compared: Macrolophus pygmaeus (Rambur), Dicyphus errans (Wolff), Dicyphus tamaninii Wagner and Deraeocoris pallens (Reuter). They were assessed on their establishment on sweet pepper plants with and without supplemental food (eggs of the flour moth Ephestia kuehniella Zeller and decapsulated cysts of the brine shrimp Artemia franciscana Kellogg) and on their effects on aphids with releases before and after aphid infestations. None of the predator species was able to control an established population of aphids on sweet pepper plants; however, the predators M. pygmaeus and D. tamaninii could successfully reduce aphid populations when released prior to an artificially introduced aphid infestation. The best results were achieved with M. pygmaeus in combination with a weekly application of supplemental food. Hence, our results demonstrate that the order and level of plant colonization by mirid predators and aphids determines how successful biological control is. Further studies are needed to evaluate the performance of mirid predatory bugs in sweet pepper crops in commercial greenhouses with multiple pests and natural enemies, in particular to understand how increased variation in food sources affects their feeding behaviour and preferences.     

Response of mirid predators to synthetic herbivore‐induced plant volatiles

Zoophytophagous plant bugs feed on plant tissue as a source of water and nutrients, besides feeding on prey. By phytophagy, mirid predators activate plant defense responses through different pathways, resulting, among others, in the release of herbivore‐induced plant volatiles (HIPVs). These compounds could repel herbivores and attract parasitoids and predators, and synthetic versions could potentially be used in biological control. Nevertheless, little is known about the influence of synthetic volatiles on mirid attraction. Using Y‐tube olfactometer trials, we evaluated the responses of Nesidiocoris tenuis (Reuter), Macrolophus pygmaeus (Rambur), and Dicyphus bolivari Lindberg (Hemiptera: Miridae), important natural enemies used to control various greenhouse pests, to 10 synthetic versions of HIPVs released from tomato (Solanum lycopersicum L., Solanaceae) plants induced by N. tenuis and M. pygmaeus. Nesidiocoris tenuis responded to five of the 10 HIPVs, whereas M. pygmaeus and D. bolivari responded to four of the 10 HIPVs. Two green leaf volatiles, (Z)‐3‐hexenyl propanoate and (Z)‐3‐hexenyl acetate, and the ester methyl salicylate (MeSA) were attractive to all three mirid predator species. Our results demonstrate that the volatiles released by tomato plants activated by N. tenuis and M. pygmaeus phytophagy are attractive to their conspecifics and also to D. bolivari. Further studies should evaluate the potential of these compounds to attract predatory mirids in the field.