Ecological rigidity and the hardness of selection in the wild.

Hutchinson's ecological theater and evolutionary play is a classical view of evolutionary ecology-ecology provides a template in which evolution occurs. An opposing view is that ecological and evolutionary changes are like two actors on a stage, intertwined by density and frequency dependence. These opposing views correspond to hard and soft selection, respectively. Although often presented as diametrically opposed, both types of selection can occur simultaneously, yet we largely lack knowledge of the relative importance of hard versus soft selection in the wild. I use a dataset of 3000 individual gall makers from 15 wild local populations over 5 years to investigate the hardness of selection. I show that enemy attack consistently favors some gall sizes over others (hard selection) but that these biases can be fine-tuned by density and frequency dependence (soft selection). As a result, selection is hard and soft in roughly equal measures, but the importance of each type varies as species interactions shift. I conclude that eco-evolutionary dynamics should occur when a mix of hard and soft selection acts on a population. This work contributes to the rapprochement of disparate views of evolutionary ecology-ecology is neither a rigid theater nor a flexible actor, but instead embodies components of both.

Evaluation of larvicidal activity and effects on post embrionary development of laboratory reared Lucilia cuprina (Wiedemann, 1830) (Diptera: Calliphoridae), treated with Brevibacillus laterosporus.

The blowfly Lucilia cuprina is an economically important livestock pest that is also associated with human myiasis. To date, methods including the application of chemical pesticides, plant extracts, insect growth regulators and a range of Bacillus thuringiensis strains have been used, with varying degrees of success, to control this pest. The present study evaluated the larvicidal activity and the induction of sub lethal effects upon post embrionary development following ingestion of 12 strains of Brevibacillus laterosporus, presented individually in the diet as spores. All strains were shown to be larvicidal, with corrected mortality levels of 29 to 54%. No significant differences were observed, in terms of larval weight at the time of abandoning the diet, in the time taken for the initiation of the pupation process, in the duration of the pupation process, the period of adult emergence or cumulative mortality during the transition from larvae to adult. However, an influence upon sex ratio was observed. This study suggests that strains of B. laterosporus hold potential for development as a tool in the biological control of L. cuprina.

Choosing between good and better: optimal oviposition drives host plant selection when parents and offspring agree on best resources.

Insect preferences for particular plant species might be subjected to trade-offs among several selective forces. Here, we evaluated, through laboratory and field experiments, the feeding and ovipositing preferences of the polyphagous leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) in relation to adult and offspring performance and enemy-free space. Female leafminers preferred laying their eggs on Vicia faba (Fabaceae) over Beta vulgaris var. cicla (Chenopodiaceae), in both laboratory and field choice experiments, although no oviposition preference was observed in no-choice tests. Females fed more often on B. v. var. cicla (no-choice test) or showed no feeding preference (choice test), even when their realized fecundity was remarkably higher on V. faba. Offspring developed faster, tended to survive better, and attained bigger adult size on the preferred host plant. Also, a field experiment showed higher overall parasitism rates for leafminers developing on B. v. var. cicla, with a nonsignificant similar tendency in field surveys. According to these results, host plant selection by L. huidobrensis appears to be driven mainly by variation in host quality. Moreover, the consistent oviposition choices for the best host and the labile feeding preferences observed here, suggest that host plant selection might be driven by maximization of offspring fitness even without a conflict of interest between parents and offspring. Overall, these results highlight the complexity of decisions performed by phytophagous insects regarding their host plants, and the importance of simultaneous evaluation of the various driving forces involved, in order to unravel the adaptive significance of female choices.

Controlling the sugar beet fly Pegomyia mixta Vill. with entomopathogenic nematodes.

Sugar beet, Beta vulgaris L. is a strategic crop of sugar industry in Egypt. It is threatened by several insect pests among most important of them is the beet fly Pegomyia mixta. This work deals with the biological control of this insect using four entomopathogenic nematodes (EPNs). The nematodes included Steinernema carpocapsae S2, Steinernema feltiae, Heterorhabditis bacteriophora (HB1-3) and Heterorhabditis bacteriophora S1. Daily mortality of larvae and pupae of P. mixta were recorded after treatment with serial concentrations (500, 1000, 2000 and 4000 infective juveniles (IJs)/ml) of each of four studied EPNs. In the laboratory all tested nematodes killed the larvae inside their mines in the sugar beet leaves and developed in their bodies in different extends. They also killed the insect pupae in the soil and developed in their bodies. Young larvae were more susceptible than old ones. New pupae were more susceptible than old ones. In the field a single spray of S. feltiae or H. bacteriophora caused 81.3 or 75.9% reduction in the larval population of the in sugar beet leaves.

Cascading host-associated genetic differentiation in parasitoids of phytophagous insects.

The extraordinary diversity of phytophagous insects may be attributable to their narrow specialization as parasites of plants, with selective tradeoffs associated with alternate host plants driving genetic divergence of host-associated forms via ecological speciation. Most phytophagous insects in turn are attacked by parasitoid insects, which are similarly specialized and may also undergo host-associated differentiation (HAD). A particularly interesting possibility is that HAD by phytophagous insects might lead to HAD in parasitoids, as parasitoids evolve divergent lineages on the new host plant-specific lineages of their phytophagous hosts. We call this process 'cascading host-associated differentiation' (cascading HAD). We tested for cascading HAD in parasitoids of two phytophagous insects, each of which consists of genetically distinct host-associated lineages on the same pair of goldenrods (Solidago). Each parasitoid exhibited significant host-associated genetic divergence, and the distribution and patterns of divergence are consistent with divergence in sympatry. Although evidence for cascading HAD is currently limited, our results suggest that it could play an important role in the diversification of parasitoids attacking phytophagous insects. The existence of cryptic host-associated lineages also suggests that the diversity of parasitoids may be vastly underestimated.

Toxicity of the venom from Nasonia vitripennis (Hymenoptera: Pteromalidae) toward fly hosts, nontarget insects, different developmental stages, and cultured insect cells.

A venom preparation from Nasonia vitripennis, a wasp ectoparasitoid of fly pupae, was assayed for lethality in different stages of insects representing ten different orders and in cultured insect cells. In most cases, the motor activity of the injected insects remained completely normal for 1-2 days after the injection and displayed none of the symptoms of paralysis commonly reported for venoms of the Hymenoptera. A natural host, the flesh fly Sarcophaga bullata, was highly sensitive in the pupal stage (LD50 = 5.4 and 5.5 VRE/g for nondiapausing and diapausing pupae, respectively), the stage that is normally parasitized, and larvae and adults were as susceptible to the venom as the pupae. Adults of another fly host, Phaenicia sericata, were nearly as sensitive (LD50 = 6.5 VRE/g), but nonhost adult flies were more tolerant. Among the other orders tested, pupae of several species (Plodia interpunctella, Trichoplusia ni, Tenebrio molitor) were more susceptible to envenomation than larval or adult stages. In fact, the highest sensitivity observed in this study (LD50 = 0.58 VRE/g) was with pupae of the cabbage looper, T. ni, a species that is not a natural host. In contrast, the larvae (LD50 = 7.23 VRE/g) and adults (LD50 = 7.48) of T. ni were far less sensitive. Adults of Nasonia vitripennis were not sensitive to their own venom (LD50 = > 533 VRE/g), although adults of another hymenopteran, Apis mellifera, were suceptible (4.62 VRE/g). Adults of Lymantria dispar, Oncopeltus fasciatus, Aphis nerii, Euborellia annulipes, Diapheromera femorata, Blattella germanica, Periplaneta americana, and Reticulitermes flavipes demonstrated a high tolerance to Nasonia venom. When tested in vitro, the venom caused cultured Lepidoptera (TN-368) and Diptera (NIH SaPe4) cells to round up, swell, and eventually die. The LC50S were 0.0014 and 0.0010 VRE/microliters for TN-368 and SaPe4 cells, respectively. Cytotoxicity was observed within 10 min after exposure to LC99 levels of venom, with 100% cell mortality at 100 min for the NIH SaPe4 cells and 24 hr for TN-368 cells. It is possible that the venom component responsible for in vivo and in vitro activities may be different, but results from the cell culture work suggest that this method offers a promising assay for quickly screening venom samples. The high susceptibility of flies and pupae of other insects to the venom, as well as its novel (nonparalytic) action suggest that it may have considerable potential for development as a biopesticide.