David J. Horn

Selective mortality of parasitoids and predators of Myzus persicae on collards treated with malathion, carbaryl, or Bacillus thuringiensis.

diagnostic loci (Hbdh was only mainly active in larvae) it can be taken for granted that the same locus is expressed in the pupae. Hence L. bryoniae and trifolii are easy to discriminate as larvae, pupae and adults. It is not known at what time the transition of the larval aGpdh-I into the adult form (cxGpdh-2) occurs during the pupal stage. There is a notable difference in heterozygosity value between the 2 species. The mean heterozygosity computed over 15 genetic loci for L. bryoniae (H = 0.123 + 0.055) is 4 times as large as that for L. trifolii (H = 0.031 + 0.025; standard errors of H were calculated from the variance among loci: Nei, 1975). According to the niche-width variation hypothesis (Van Valen, 1965) L. trifolii should be as polymorphic as L. bryoniae as both species have a comparable host plant range (as a parameter of niche breadth). Conclusions, however, must remain very tentative as we are dealing with the nth laboratory generation and we do not know much of processes that may influence heterozygosity levels, such as bottlenecks, in the cultures. We will continue our study with the characterisation of other important or potentially important pests within the genus Liriomyza. We thank Anton van der Linden, Glassh. Crops Res. & Exp. Station, Naaldwijk for providing laboratory culture material, Ms. L. J. W. de Goffau for the identifications.

Vegetational background and parasitism of larval diamond‐back moth on collards

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Effect of Ant Attendance by Monomorium minimum (Buckley) (Hymenoptera: Formicidae) on Predation and Parasitism of the Soybean Aphid Aphis glycines Matsumura (Hemiptera: Aphididae)

Ant attendance is known to affect the population dynamics of aphids and may increase or decrease aphid populations through stimulation, predation, or protection. In this study, we performed a series of laboratory experiments to examine the effects of ant attendance on populations of the soybean aphid Aphis glycines. Aphid colonies were exposed to the predators Harmonia axyridis (Coccinellidae) and Orius insidiosus (Anthocoridae) and a parasitoid Aphidius colemani (Aphidiidae) in the presence and absence of attending Monomorium minimum (Formicidae). We also tested for direct effects of ant attendance in the absence of natural enemies. Ants attending soybean aphid populations were observed harassing or killing O. insidiosus and H. axyridis. Attendance interfered with both predator species, resulting in reduced predation and an increase in aphid numbers up to 10-fold in the presence of ants. Ants were not observed directly interfering with the parasitoid A. colemani, but the number of parasitized aphids was higher in aphid colonies that were left unattended by ants.

Sex ratio, pupal parasitism, and predation in two declining populations of the bagworm, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae).

Abstract. 1. Two populations of bagworms were censused in Ohio for 6 and 5 years respectively, to determine the influence of major pupal mortality factors. Bagworm densities declined from 2.3 bags per 30 cm of terminal branch to zero.

Oil Pipeline Corridor Through an Intact Forest Alters Ground Beetle (Coleoptera: Carabidae) Assemblages in Southeastern Ohio

Abstract Litter-dwelling ground beetle (Coleoptera: Carabidae) assemblages were monitored 1 yr after the construction of a corridor for installation of an oil pipeline along a xeric ridge-top forest in southeastern Ohio. After the creation of the corridor, three distinct habitats were evident in these sites: open corridor, ecotone areas around the corridor, and undisturbed forest interior. Carabidae were collected using directional pitfall traps that were placed parallel and perpendicular to the corridor in each of the three habitats. Results indicate that more carabids were present in the ecotone than in the other two habitats. Carabid diversity as estimated by rarefaction was highest in the corridor followed by ecotone and forest interior. Generalist and forest specialists such as Synuchus impunctatus (Say), Carabus goryi Dejean, and Pterostichus trinarius (Casey) were present in greater numbers in the forest interior and ecotone assemblages. In contrast, open-habitat specialists such as Harpalus pensylvanicus (DeGeer) and Selenophorus opalinus (LeConte) were present in greater numbers in the corridor assemblages. Carabid assemblages of the corridor were distinct from those of the ecotone and forest interior, whereas the latter two habitats had very similar assemblages. The successional pathway of the corridor carabid assemblage will therefore be likely different from that of the forest interior and ecotone. Overall, results indicate that construction of the oil pipeline corridor had significant short-term effects on the carabid numbers, diversity, and species composition because of ensuing habitat changes and fragmentation of the forest.

A stochastic model for simulation of interactions between phytophagous spider mites and their phytoseiid predators

A stochastic predator/prey model describing the interaction betweenTetranychus urticae andPhytoseiulus persimilis in investigated via computer simulations and pilot experiments on Lima beans in a greenhouse. Most demographic events, including predation, death due to unknown causes, dispersal, and oviposition, are modelled as stochastic processes. Transitions from eggs to nymphs and from nymphs to adults are deterministic, as are management decisions (release of predators and application of miticide). Computer simulations provide adequate and realistic representations of biological processes, and the model shows stability over a range of inputs. Experimental validation of the model continues. Predictions of the model for optimal predator release or optimal timing of acaricide application have yet to be tested experimentally.

Laboratory selection of greenhouse whitefly for resistance to malathion

A strain of the greenhouse whitefly (Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae)) with a history of insecticide exposure was selected with malathion sufficient to cause 80–90% mortality. After 13 generations, malathion resistance had increased 55‐fold, and a slight (1.7 ×) increase in resmethrin resistance was noted. There was no cross‐resistance to dichlorvos, methomyl or permethrin.