Functional response of Franklinothrips vespiformis (Thysanoptera: Aeolothripidae) to eggs and nymphs of Bemisia tabaci (Hemiptera: Aleyrodidae).

The Middle East Asia Minor 1 biotype of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is a greenhouse and field crop pest of global significance. The objective of this study was to assess the potential of the generalist predatory thrips, Franklinothrips vespiformis Crawford (Thysanoptera: Aeolothripidae), as a biological control agent for B. tabaci. This was achieved by determining the functional responses of F. vespiformis larvae and adults to the egg and nymphal stages of B. tabaci under laboratory conditions. Analyses consisted of 10 replicates of each predator and prey stage combination on bean leaf discs for a 24-h period. Following logistic regression analyses to determine the functional response type exhibited, response parameters were estimated with nonlinear least squares regression using Roger's equation. Results showed that F. vespiformis larvae and adults exhibited a Type II functional response when feeding on immature B. tabaci. The handling times (Th) of F. vespiformis larvae and adults were magnitudes higher for B. tabaci nymphs than they were for eggs, which were in part driven by the higher attack rates (a) observed on eggs. The maximum attack rate (T/Th) for B. tabaci eggs and nymphs exhibited by first-stage larvae, second-stage larvae, and adult F. vespiformis increased with increasing predator age. Results from this study suggest that F. vespiformis larvae and particularly adults are promising biological control agents for B. tabaci and are efficient predators at both low and high prey densities.

The Effects of Temperature and Host Stage on Development Rate of Parasitoids of Giant Whitefly Aleurodicus dugesii (Hemiptera: Aleyrodidae).

The effects of rearing temperature and host stage parasitized on the development of three parasitoid species; Encarsia noyesi Hayat (Hymenoptera: Aphelinidae), Idioporus affinis LaSalle & Polaszek (Hymenoptera: Pteromalidae), and Entedononecremnus krauteri Zolnerowich & Rose (Hymenoptera: Eulophidae) were investigated. These parasitoids are part of the biological control program for the giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae) in the United States. Temperature and host-dependent development was assessed for each species using the nonlinear Brière-1 model and simple linear regression to obtain critical thermal parameters. All three parasitoids successfully developed at constant temperatures ranging from 15°C to 30°C, which was narrower to their predicted thermal limits due to thermal constraints of A. dugesii. There were significant effects of both temperature and A. dugesii nymphal stage parasitized on immature parasitoid development times. All three parasitoid species' development time decreased as nymphal stage age increased. Thermal tolerance limits and development times varied by parasitoid species. The results of these findings in the context of biological control potential are discussed.

Comparison of the phytoseiid mites Amblyseius swirskii and Amblydromalus limonicus for biological control of chilli thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae).

The chilli thrips, Scirtothrips dorsalis Hood, is a recently established pest in the USA and poses a serious risk to many economically important ornamental and food crops. In this study the biological control potential of the phytoseiid mites Amblydromalus limonicus (Garman and McGregor) and Amblyseius swirskii (Athias-Henriot) was compared by examining their predation and oviposition rates when fed different developmental stages of S. dorsalis. Gravid females were offered 10 individuals of either first instar, second instar, or adult S. dorsalis using a no-choice leaf disc bioassay and oviposition and predation rates were assessed daily for 2 and 3 days, respectively. There was no significant difference in predation and oviposition rates between mite species fed specific S. dorsalis life stages. There was, however, a significant effect of S. dorsalis life stage on the oviposition and predation rates observed for each mite species. The larval stage was the most preferred stage for both mite species, with A. swirskii consuming 4.6-6.3 and A. limonicus 4.8-6.4 individuals/day compared to only 1.6-1.7 adults/day consumed by both species. Female A. swirskii and A. limonicus laid 0.55-0.75 and 0.73 eggs/day on the two larval stages, respectively, compared to only 0.25-0.30 eggs/day observed for individuals feeding on adults. Although the results showed that the biological control potential of both mite species was similar, having an additional predator available that may be as effective as A. swirskii, a proven control agent against S. dorsalis in the field, warrants additional research into its potential utility.

Temperature-Dependent Development and Survival of Giant Whitefly Aleurodicus dugesii (Hemiptera: Aleyrodidae) Under Constant Temperatures.

The invasive giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae) is a pest of over 300 plants species in the United States, many of which are economically important ornamentals and crops. Development and survival of A. dugesii was assessed at seven constant temperatures ranging from 10 to 35°C to provide a basis for phenological forecasting and assist in enhancing current biological control strategies. Complete development occurred from 15 to 28°C, with partial development occurring at 30°C. Development time differed between sexes, with males developing 2 (at 25°C) to 6 (at 15 and 28°C) d faster than females. Adult survival was highest at 25°C (65.4%), with survival rate declining rapidly at other temperatures. The relationship between temperature and development was evaluated using five nonlinear models (Lactin-2, Brière-1 and 2, Beta, and LRF). Additionally, the simple linear regression was used to calculate developmental degree-days (DDs). While all five nonlinear models evaluated fit the data well, the Brière-1 model provided the best fit of the data and estimated the optimal (25.3°C), lower (9.9°C), and upper (30.0°C) developmental thresholds for male and female complete development. Using linear regression, DDs for complete development were calculated as 408 and 435 for males and females, respectively. The results of this study emphasize A. dugesii survival and development under varied temperature conditions.

Host Stage Preferences of Encarsia noyesi, Idioporus affinis, and Entedononecremnus krauteri: Parasitoids of the Giant Whitefly Aleurodicus dugesii (Hemiptera: Aleyrodidae).

Parasitoid wasps released as biological control agents may experience strong interspecific competition, which can lead to a reduction in pest control. The effects of competition can be mitigated if niche partitioning exists between species, such as parasitism preferences for different host stages. We examined host stage preferences for the parasitoids Encarsia noyesi Hayat (Hymenoptera: Aphelinidae), Idioporus affinis LaSalle and Polaszek (Hymenoptera: Pteromalidae), and Entedononecremnus krauteri Zolnerowich and Rose (Hymenoptera: Eulophidae). These parasitoids were introduced to the United States to control the giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae), a pest of many economically important plants. Host stage preferences were examined using multiple metrics including: parasitism rates, relative preferences, handling times, and initial stage parasitism frequency. The data indicated differences in parasitoid preference hierarchies for the four A. dugesii nymphal stages. All A. dugesii nymphal stages were parasitized by I. affinis, which exhibited preference for the third instar. Unlike I. affinis, the first instar was not parasitized by E. noyesi, and its preference hierarchy differed with the fourth instar being the most preferred stage. The observed host-use breadth of E. krauteri was the narrowest observed of the three parasitoid species, only parasitizing the fourth and third instars, with a clear preference for the former. The observed differences in host-use breadth and stage preferences between parasitoid species in this system may promote their long-term coexistence in the field and facilitate biological control. Potential factors underlying the preferences exhibited by these parasitoids and their implications for biological control are discussed.

Flight phenologies of the southeastern Ips species (Coleoptera: Curculionidae: Scolytinae) and some associated Coleoptera in central and southern Louisiana.

A year-long flight phenology study was undertaken from 15 July 2009 to 7 July 2010 in central and southeastern Louisiana to estimate the temporal flight patterns of the three southeastern Ips species: Ips grandicollis (Eichhoff), Ips avulsus (Eichhoff), and Ips calligraphus (Germar) (Coleoptera: Curculionidae: Scolytinae) as well as some of their predatory and phloem-feeding coleopteran associates. The southeastern Ips species play important roles as decomposers in forest ecosystems, but can cause ecological and economic damage during epidemic population phases. In total, 282,761 individuals of the three southeastern Ips species were collected using Ips pheromone-baited multiple funnel traps during the study period. Two major Ips activity peaks were observed during 16 September to 7 October of 2009 and 24 March to 15 April of 2010. In total, 9,139 associated Coleoptera were also collected. Greater than 95% of the total number of associated Coleoptera collected were represented by histerids from the genus Platysoma (4,487; 49.1% of total), the trogossitid Temnoscheila virescens (F.) (2,107; 23.1%), cerambycids from the genus Monochamus (1,013; 11.1%), and Acanthocinus obsoletus (Olivier) (743; 8.1%), and the clerid Thanasimus dubius (F.) (477; 5.2%). Results showed that the associates fell into four temporal groups: the winter and spring active species T. dubius; the spring active species Rhagium inquisitor (L.) and histerids from the genus Platysoma; the spring and summer active species T. virescens, Buprestis lineata F., and Monochamus carolinensis (Olivier); and the summer through fall active species A. obsoletus and Monochamus titillator (F.).

Molecular evidence of facultative intraguild predation by Monochamus titillator larvae (Coleoptera: Cerambycidae) on members of the southern pine beetle guild.

The southern pine bark beetle guild (SPBG) is arguably the most destructive group of forest insects in the southeastern USA. This guild contains five species of bark beetles (Coleoptera: Curculionidae: Scolytinae): Dendroctonus frontalis, Dendroctonus terebrans, Ips avulsus, Ips calligraphus, and Ips grandicollis. A diverse community of illicit receivers is attracted to pheromones emitted by the SPBG, including the woodborers Monochamus carolinensis and Monochamus titillator (Coleoptera: Cerambycidae). These woodborers have been traditionally classified as resource competitors; however, laboratory assays suggest that larval M. carolinensis may be facultative intraguild predators of SPBG larvae. This study used polymerase chain reaction (PCR)-based molecular gut content analyses to characterize subcortical interactions between M. titillator and members of the SPBG. The half-lives of SPBG DNA were estimated in the laboratory prior to examining these interactions in the field. A total of 271 field-collected M. titillator larvae were analyzed and 26 (9.6 %) tested positive for DNA of members of the SPBG. Of these larvae, 25 (96.2 %) tested positive for I. grandicollis and one (3.8 %) for I. calligraphus. Failure to detect D. terebrans and D. frontalis was likely due to their absence in the field. I. avulsus was present, but primers developed using adult tissues failed to amplify larval tissue. Results from this study support the hypothesis that larval Monochamus spp. are facultative intraguild predators of bark beetle larvae. Additionally, this study demonstrates the capabilities of PCR in elucidating the interactions of cryptic forest insects and provides a tool to better understand mechanisms driving southern pine beetle guild population fluctuations.