Casey D. Butler

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae): life history, relationship to plant diseases, and management strategies

The potato/tomato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) has been a major pest of solanaceous crops for decades. This pest can cause damage to crop plants by direct feeding and, as has been recently discovered, by transmitting the bacterial pathogen Candidatus Liberibacter psyllaurous (a.k.a. Ca. L. solanacearum). Many studies have been conducted to determine the relationship of this pest to plant injury and to develop management strategies to alleviate the damage caused by this pest in a wide variety of solanaceous plants. Studies in the past decade have documented substantial genetic variability in this invasive species, enhanced our rapidly-evolving understanding of the interactions between the insect and the pathogen it carries, and improved our appreciation of the invasive potential of the pest. This review seeks to provide a comprehensive update to B. cockerelli life history, relationship to plant diseases, and the current state of management strategies against B. cockerelli.

Effects of pollutants on bottom-up and top-down processes in insect-plant interactions.

Bottom-up (host plant quality) and top-down (natural enemies) forces both influence the fitness and population dynamics of herbivores. However, the impact of pollutants acting on these forces has not been examined, which prompted us to review the literature to test hypotheses regarding this area of research. A comprehensive literature search found 126 references which examined fitness components and population dynamics of 203 insect herbivores. One hundred and fifty-three of the 203 herbivores (75.4%) had fitness impacted due to bottom-up factors in polluted environments. In contrast, only 20 of the 203 (9.9%) had fitness significantly impacted due to top-down factors in polluted environments. The paucity of results for top-down factors impacting fitness does not necessarily mean that top-down factors are less important, but rather that fewer studies include natural enemies. We provide a synthesis of available data by pollution type and herbivore guild, and suggest future research to address this issue.

Effects of Insecticides on Behavior of Adult Bactericera cockerelli (Hemiptera: Triozidae) and Transmission of Candidatus Liberibacter psyllaurous

ABSTRACT The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera:Triozidae), is a serious pest of potatoes (Solanum tuberosum L.) that can cause yield loss by direct feeding on crop plants and by vectoring a bacterial pathogen, Candidatus Liberibacer psyllaurous. Current pest management practices rely on the use of insecticides to control the potato psyllid to lower disease incidences and increase yields. Although many studies have focused on the mortality that insecticides can cause on potato psyllid populations, little is known regarding the behavioral responses of the potato psyllid to insecticides or whether insecticides can decrease pathogen transmission. Thus, the objectives of this study were to determine the effects of insecticides on adult potato psyllid behaviors, the residual effects of insecticides on potato psyllid behaviors over time, and effects of these insecticides on Ca. L. psyllaurous transmission. Insecticides tested included imidacloprid, kaolin particle film, horticultural spray oil, abamectin, and pymetrozine. All insecticides significantly reduced probing durations and increased the amount of time adult psyllids spent off the leaflets, suggesting that these chemicals may be deterrents to feeding as well as repellents. Nonfeeding behaviors such as tasting, resting, and cleaning showed variable relationships with the different insecticide treatments over time. The insecticides imidacloprid and abamectin significantly lowered transmission of Ca. L. psyllaurous compared with untreated controls. The implications of our results for the selection of insecticides useful for an integrated pest management program for potato psyllid control are discussed.

Defensive Response of Soybean Aphid (Hemiptera: Aphididae) to Predation by Insidious Flower Bug (Hemiptera: Anthocoridae)

Abstract During research on the life history characteristics of insidious flower bug, Orius insidiosus (Say), fed soybean aphids, Aphis glycines Matsumura, the mouthparts of some predators were covered by a substance excreted from the cornicles of attacked aphids. The cornicle exudate was found to encumber both nymphs and adults of O. insidiosus causing death because of molting failure and starvation. Among predator stages, first instars were most severely affected. Feeding frequency affected the number of predators affected by the exudate, with predators fed more often having higher rates of exudate exposure and mortality. Soybean aphids produce exudate during all life stages, and its production does not seem to compromise the survival of the aphid. The exudate also seems to contain an alarm pheromone as evidenced by increased movement and activity of aphids in the vicinity of exudate-producing aphids. The potential impact of the aphid’s cornicle defenses on aphid–predator dynamics in soybean, Glycine max (L.) Merr., is discussed.

Feeding disruption of potato psyllid, Bactericera cockerelli, by imidacloprid as measured by electrical penetration graphs

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a serious pest of potatoes that can cause yield loss by direct feeding and by transmitting a bacterial pathogen, Candidatus Liberibacter psyllaurous (also known as Candidatus L. solanacearum), which is associated with zebra chip disease of this crop. Current pest management practices rely on the use of insecticides for control of potato psyllid to lower disease incidences and increase yields. Imidacloprid is typically applied at potato planting, and it remains unknown if imidacloprid has any effect on potato psyllid feeding behavior. Thus, our specific objectives of this study were to determine and characterize the effects of imidacloprid treatment (0.11 ml l−1) to potato plants on adult potato psyllid feeding behavior 1, 2, and 4 weeks post‐application. Electrical penetration graph (EPG) recordings of potato psyllid feeding revealed six EPG waveforms, which include non‐probing (NP), intercellular stylet penetration (C), initial contact with phloem tissue (D), salivation into phloem sieve elements (E1), phloem sap ingestion (E2), and ingestion of xylem sap (G). The number of NP events and the duration of individual NP events significantly increased on plants treated with imidacloprid compared with untreated controls. Potato psyllids exhibited significant decreases in the number of phloem salivation events on plants treated with imidacloprid. Waveform durations and waveform durations per event for E2 and G were significantly decreased for psyllids on plants treated with imidacloprid compared with untreated controls. These data suggest that the effective use of imidacloprid to reduce transmission of Ca. Liberibacter psyllaurous is related to the negative effects of imidacloprid on psyllid feeding.

Effects of terrestrial pollutants on insect parasitoids

Parasitoids are important organisms in the regulation of insect herbivores in natural, urban, and agricultural ecosystems. The impact of pollutants acting on parasitoids has not been extensively reviewed. This prompted us to propose a falsifiable null hypothesis (pollutants have no effects on parasitoids) and two alternative hypotheses (pollution negatively or positively affects parasitoids) to assess in the available literature the effects of pollutants acting on parasitoids. We found 26 studies examining 39 biological systems that met our criteria for inclusion. Of these studies, 18 of the 39 biological systems (46.2%) supported the null hypothesis while 18 (46.2%) supported the first alternative hypothesis in which pollutants exhibited negative effects on parasitoids. Only a small percentage of the studies (7.6%, 3 of 39) supported the second alternative hypothesis suggesting that pollutants had positive effects on parasitoids. We provide a synthesis of the available data by pollution type, summarize trends for different pollutants, and suggest future areas of research.

Identification and Impact of Natural Enemies of Bactericera cockerelli (Hemiptera: Triozidae) in Southern California

ABSTRACT Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is a major pest of potato, (Solanum tuberosum L.), tomato (Solanum lycopersicum L.), and peppers (Capsicum spp.). The purpose of our research was to identify and determine the impact of natural enemies on B. cockerelli population dynamics. Through 2 yr of field studies (2009–2010) at four different sites and laboratory feeding tests, we identified minute pirate bug, Orius tristicolor (White) (Hemiptera: Anthocoridae); western bigeyed bug, Geocoris pallens Stål (Hemiptera: Geocoridae), and convergent lady beetle, Hippodamia convergent Guérin-Méneville (Coleoptera: Coccinellidae) as key natural enemies of B. cockerelli in southern California potatoes, tomatoes, and bell peppers. In natural enemy exclusion cage experiments in the potato crop and in American nightshade, Solanum americanum Miller, the number of B. cockerelli surviving was significantly greater in the closed cage treatments, thus confirming the affect natural enemies can have on B. cockerelli. We discuss how this information can be used in an integrated pest management program for B. cockerelli.

Voracity and prey preference of insidious flower bug (hemiptera: anthocoridae) for immature stages of soybean aphid (hemiptera: aphididae) and soybean thrips (thysanoptera: thripidae).

Abstract The generalist predator, Orius insidiosus (Say), is an important natural enemy of the soybean aphid, Aphis glycines Matsumura. Soybean thrips, Neohydatothrips variabilis (Beach), serve as an important prey resource for O. insidiosus in soybeans, sustaining the predator’s population before the arrival of the soybean aphid. Although generalist predators can forage on a broad range of prey, they may show distinct preferences for particular prey, attacking prey at levels disproportionate to their relative numbers. To assess the preference of O. insidiosus for soybean aphid and soybean thrips, attack rates of nymphal and adult O. insidiosus were measured in the laboratory. For both adults and nymphs, the number of prey attacked increased as more prey were provided. For nymphs, the total number of prey attacked increased as the predator matured. In general, the number of prey attacked by adult predators was relatively constant as the predator aged. Both O. insidiosus nymphs and adults displayed a preference for soybean thrips, by disproportionately attacking soybean thrips over soybean aphid regardless of the relative densities of the two prey. We discuss implications of this preference on O. insidiosus life history characteristics and the potential impact on O. insidiosus–prey dynamics in the field.

Predicting population dynamics of the parasitoid Cotesia marginiventris (Hymenoptera: Braconidae) resulting from novel interactions of temperature and selenium.

Abstract Changes in trophic level interactions due to global climate change and the increasing occurrence of pollution are likely to have consequences for natural enemies. Specifically, information regarding the effects of these factors on insect parasitoids is relatively sparse. We examined the individual and joint effects of temperature and the pollutant selenium on the fitness correlates of the parasitoid wasp Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), parasitizing Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae). Our specific objective was to determine in a factorial experiment how three temperatures (constant 28.6°C, constant 33°C and a fluctuating temperature between 28.6 and 33°C) and three concentrations of seleno-dl-methionine (0.00, 21.21, and 42.42 µg/g) affected the parasitoids fitness and life history. Parasitoids failed to complete development at the constant 33°C, but developed significantly faster at the fluctuating temperature compared to the constant 28.6°C. There were significant declines due to increased temperature, but not selenium, on C. marginiventris survival time, adult body weight, body size, hind tibia length, female life span and number of progeny that survived to adulthood. Mean generation times and the intrinsic rate of increase (r) further show that both of these life table statistics declined under conditions of increased temperatures. We discuss the implications of these results in helping to understand and predict the effectiveness of biological control programs and pest management strategies as climate changes in the presence of metal and metalloid pollution.

New records of hyperparasitism of Tamarixia triozae (Burks) (Hymenoptera: Eulophidae) by Encarsia spp. (Hymenoptera: Aphelinidae) in California

Tamarixia triozae (Burks 1943) (Hymenoptera: Eulophidae) is a primary parasitoid of the potato/tomato psyllid, Bactericera cockerelli (Sulc, 1909) (Hemiptera: Triozidae), which is a serious pest of solanaceous crops in North America, Central America, and New Zealand (Liu & Trumble 2007, Gill 2006, Teulon et al. 2009, Crosslin et al. 2010). T. triozae has an extensive geographic distribution in the United States (Arizona, California, Colorado, Idaho, Kansas, Montana, New Mexico, Washington) and also has been found in recent years in Mexico (Burks 1943, Pletsch 1947, Jensen 1957, Johnson 1971, Lomeli-Flores & Bueno Partida 2002). In 2009, this parasitoid was imported from Mexico to New Zealand as a potential classical biological control agent against B. cockerelli (Workman & Whiteman 2009). There is only one report documenting the case of hyperparasitism of T. triozae, which was reported by Pletsch (1947) of a single, unknown pteromalid that was reared from a T. triozae larva. During the summer and fall of 2010 as part of our research to document the identification and impact of natural enemies on the potato psyllid, we documented new records of males of Encarsia pergandiella Howard, 1907 (Hymenoptera: Aphelinidae) and a single record of a male tentatively identified as Encarsia peltata (Cockerell, 1911) hyperparasitizing T. triozae on tomato (Solanum lycopersicum Linnaeus, 1753) (Solanaceae) and bell pepper (Capsicum annuum Linnaeus, 1753) (Solanaceae) plantings in southern California.