Walker A. Jones

Effects of selected insecticides on Diadegma insulare (Hymenoptera: Ichneumonidae), a parasitoid of Plutella xylostella (Lepidoptera: Plutellidae)

Effects of eight insecticides on Diadegma insulare (Cresson), a parasitoid of the diamondback moth, Plutella xylostella L., were evaluated under the laboratory conditions. The insecticides were three azadirachtin-based products (Ecozin, Agroneem and Neemix), two Bacillus thuringiensis (Bt) products (Xentari and Crymax), indoxacarb, spinosad, and λ-cyhalothrin. When D. insulare pupae were treated, none of the insecticide treatments except λ-cyhalothrin significantly reduced adult emergence, with 76–90% adults emerged from the treated pupae. In the λ-cyhalothrin treatment, only 10% D. insulare pupae produced adult wasps. Indoxacarb, spinosad, and λ-cyhalothrin caused 100% D. insulare adult mortality in 24 h in Petri dishes sprayed with insecticides in the contact bioassays, and 95.8, 100 and 95.8% adult mortality in 24 h in the ingestion bioassays, respectively. In contrast, all three azadirachtin-based insecticides and the two Bt-insecticides caused only 0–10.4% mortality of D. insulare adults after ingestion. The surviving D. insulare from ingestion treatments with Bt- and azadirachtin-insecticides parasitized 50.8–67.6% of P. xylostella larvae, respectively, compare to 72.1% for the water control. After ingesting indoxacarb, spinosad and λ-cyhalothrin mixed in honey–water, both the females and the males lived significantly shorter than those ingesting Bt- and azadirachtin-insecticides and the non-insecticide honey–water. Effects of leaf residues of indoxacarb, spinosad and λ-cyhalothrin varied significantly. The leaf residues of spinosad had the least effects on D. insulare adults, and 7- and 10-day-old residue only caused 5.6 and 7.4% mortality in 24 h, whereas 10-day-old leaf residues of indoxacarb and λ-cyhalothrin caused 40.7 and 57.4% mortality in 24 h, respectively.

From Asian curiosity to eruptive American pest: Megacopta cribraria (Hemiptera: Plataspidae) and prospects for its biological control

The kudzu bug or bean plataspid, Megacopta cribraria (Fabricius), is native to Asia where it appears to be widely distributed (although the taxonomy is not entirely clear), but is infrequently a pest of legumes. This bug appeared in 2009 in the southeastern United States, where it is closely associated with kudzu, Pueraria montana Lour. [Merr.] variety lobata [Willd.] Maesen & S. Almeida. However, the insect has become a consistent economic pest of soybeans, Glycine max (L.) Merr., and some other leguminous crops in areas where large numbers can build in kudzu, in addition to being a considerable nuisance in urban landscapes where kudzu occurs. The insect has remarkable capacity for movement and has spread rapidly from nine Georgia counties in 2009 to seven states in 2012. Despite being a nuisance in urban areas and a crop pest, high populations of the bug also reduce the biomass of kudzu, which is itself a seriously problematic invasive weed, complicating the status of M. cribraria in its expanded range. Extant predators and a pathogen in the US have been observed attacking kudzu bugs in the laboratory and field, but no parasitism of eggs or nymphs has been observed to date. A single record of parasitism of an adult kudzu bug by a tachinid fly is known from the US, but no other adult parasitism has been observed in the US or elsewhere. Extant enemies may eventually significantly reduce the bug’s populations, but at present native enemies appear to be insufficient for the task, and exotic enemies from the kudzu bug’s native range may offer the best possibility for effective biological control in the US. Based on the available literature, the best option for an importation biological control program appears to be the platygastrid egg parasitoid Paratelenomus saccharalis (Dodd) because of its apparent host specificity, intimate biological linkages with M. cribraria, and wide geographic distribution in the Eastern Hemisphere. Other natural enemies may eventually emerge as good candidates for importation, but at present P. saccharalis appears to be the most promising.

The effect of varying Bemisia argentifolii and Eretmocerus mundus ratios on parasitism

We investigated the effects of different host: parasitoid ratios on the efficacy of the parasitoid Eretmocerus mundus attacking the silverleaf whitefly, Bemisia argentifolii. When host density was held constant (100 second instars) and parasitoid density was decreased from 15 to 1 females, the percentage of total host mortality was significantly lower at low parasitoid densities. The number of host nymphs killed, and the number of female parasitoid progeny per female, increased 3.6 and 20.4 times, respectively. The emergence rate, sex ratio, longevity, and body lengths of progeny were significantly larger at the lowest parasitoid density while developmental time was significantly shorter. When the number of hosts was increased from 5 to 250 and parasitoid density was held constant (5 females), the percentage of nymphal mortality decreased 1.6 times. The percentage of desiccated nymphs was significantly highest (65.7%) at the lowest host density, while percentage parasitism (34.3%) was significantly lowest at the lowest host density. The data could be described using a Type I functional response curve. We propose a generalized index of efficacy (GIE) to summarize and compare the total effects of parasitoid--host ratios. This index showed that the most efficient ratio was one parasitoid female per ten second instar host nymphs.

Interactions Among Two Species of Eretmocerus (Hymenoptera: Aphelinidae), Two Species of Whiteflies (Homoptera: Aleyrodidae), and Tomato

Abstract Laboratory experiments were conducted to determine the influence of two tomato (Lycopersicum esculentum Miller) varieties (‘Trust’ and ‘Floridade’) on the biology of two whitefly species, Bemisia argentifolii Bellows & Perring and Trialeurodes vaporariorum (Westwood), and the interactions of host plant and whiteflies on the biology and parasitization of two parasitoid species, Eretmocerus eremicus Rose & Zolnerowich (native) and Eretmocerus mundus Mercet (exotic). Natural mortality, developmental time, and fecundity of B. argentifolii were not significantly different from those of T. vaporariorum on either tomato variety. The two species of Eretmocerus responded differently to the whitefly hosts. Eretmocerus mundus developed significantly faster, produced more progeny, and had greater parasitism and rate of emergence in B. argentifolii than in T. vaporariorum. Eretmocerus eremicus performed similarly on both whitefly species except that its females deposited more eggs in B. argentifolii than in T. vaporariorum nymphs. Females of both parasitoid species emerging from T. vaporariorum were significantly larger than those emerged from B. argentifolii. Tomato variety had no significant effect on the two parasitoid species. Eretmocerus eremicus attack both whiteflies efficiently and it can be used as a single species for whitefly management.

Host range of the European, rhizome-stem feeding scale Rhizaspidiotus donacis (Hemiptera: Diaspididae), a candidate biological control agent for giant reed, Arundo donax (Poales: Poaceae) in North America

Abstract The armored scale Rhizaspidiotus donacis (Leornardi) was evaluated as a potential biological control agent of the invasive reed grass Arundo donax in North America. No-choice tests, native range field surveys and non-target host exposures were used to determine the fundamental host range of the scale collected from Caloma, Spain and Perpignan, France. Thirty-five species, including two genotypes of A. donax and seven ecotypes of Phragmites australis, along with closely related grasses, economic grasses and habitat associates were tested. In quarantine no-choice testing using releases of 200 crawlers per plant, normal development of R. donacis was observed on A. donax and A. formosana, with very limited survival to the adult stage on Spartina alterniflora and Leptochloa spp. In follow-up studies using 1000 crawlers per plant, 10 live adult females were found on Leptochloa virgata, and one adult female on Spartina alterniflora, but average adult female abundance per plant was (2580%) 26-times lower on L. virgata and over (39,090%) 100-times lower on S. alterniflora than on A. donax. Field surveys were conducted at five locations in Spain and France at which A. donax infested with R. donacis, co-occurred with two non-target species of concern and R. donacis was only found on A. donax. Six-month field host exposures in Spain using potted Leptochloa plants entwined with heavily infested A. donax confirmed that R. donacis is specific to Arundo under field conditions. Based on our results, the scale R. donacis appears to be specific to the genus Arundo and is unlikely to harm native or cultivated plants in the Americas.

Biology and Biometry of Sharpshooter Homalodisca coagulata (Homoptera: Cicadellidae) Reared on Cowpea

Abstract Stage-specific survival, growth, developmental biology, and biometry of the sharpshooter Homalodisca coagulata (Say) were studied in the laboratory under controlled conditions of 27 ± 1°C, 65 ± 5 RH, and a photoperiod of 14:10 (L:D) h. Nymphs and adults were individually reared on excised cowpea, Vigna unguiculata L. Walp., plants maintained in floral aquapics containing a hydroponic solution. Embryonic development of eggs was completed in 7.1 ± 0.8 d with 92.6% of the incubated eggs hatching. Nymphs molted five times, and the nymphal period of 61 ± 2.9 d for females was 1.2-fold significantly longer than that of males. The second nymphal stage was the shortest for both sexes (6.1 ± 0.5 d for females and 5.8 ± 0.8 d for males), whereas the last instar was the longest for females only. Stage-specific mortality was similar between instars; ≈36% of the nymphs molted to adults. H. coagulata adult sex ratio was not significantly different from a 1:1 ratio. Adult females lived 52 ± 11 d, and females deposited an average of 194 ± 35 eggs each. Analysis of life table statistics indicated that populations of H. coagulata increased at a rate of 1.045 per day and doubled within 15.6 d. The different H. coagulata growth stages were well described by body length, head capsule width, and hind tibia length; however, analysis of frequency distribution showed that head capsule width was the most suitable parameter for distinguishing the immature developmental stages of H. coagulata.

Population Genetic Structure of Homalodisca coagulata (Homoptera: Cicadellidae), the Vector of the Bacterium Xylella fastidiosa Causing Pierce’s Disease in Grapevines

Abstract In the current study, inter-simple sequence repeat (ISSR) primers (p-13 and p-15) were used to estimate the population genetic structure of the sharpshooter Homalodisca coagulata (Say) (Homopera: Cicadellidae). Eighteen populations from throughout the United States and a population from Tahiti, French Polynesia, were analyzed. Populations were arbitrarily assigned to three regions: southeastern, southwestern, and western. Exact tests for population differentiation indicated highly significant differences in marker frequencies among the 18 populations with both primers. Analyses of molecular variance also indicated significant geographic structuring with both primers. A dendrogram based on Reynolds coancestry distance performed with p-15 clustered the U.S. populations into two main groups. The southeastern populations were grouped into one cluster and the southwestern and western populations into a second cluster. Within the western region, dendrograms produced with p-13 and p-15 showed in both cases that two populations (Edison and Bakersfield) clustered as outliers. The average divergence (D) among all populations was 0.099. Divergence values of 0.254, 0.103, and 0.102 were observed when comparing Bakersfield and the southeastern, southwestern, and western populations, respectively. Within the western region, D values for Bakersfield were 1.8- (p-13) and 2.4-fold (p-15) higher than the D of the western populations. The present results suggest that a subset of insects in California may have their origins in the southwestern region (Texas); furthermore, these results are suggestive of more than one founding event in California and/or biotypes or geographic races.

Olfactory Responses of Anaphes iole (Hymenoptera: Mymaridae) to Volatile Signals Derived from Host Habitats

Anaphes iole Girault is a frequent parasitoid of Lygus spp. eggs in the United States, and has potential as a biological control agent against Lygus hesperus Knight in different crops. Feeding and oviposition by L. hesperus induce emission of plant volatiles, but studies to date do not address the role of plant volatiles in the host-searching behavior of A. iole. In this study, a four-arm olfactometer was used to test the responses of female parasitoids to odors emanating from cotton (Gossypium hirsutum L., Malvaceae) plants damaged by L. hesperus females, L. hesperus males, larvae of the nonhost Spodoptera exigua Hubner, or mechanically, or to odors from L. hesperus females alone. In addition, various plants damaged by L. hesperus females were evaluated in the olfactometer: cotton, alfalfa (Medicago sativa L., Fabaceae), common groundsel (Senecio vulgaris L., Asteraceae), annual ragweed (Ambrosia artemisifolia L., Asteraceae), and redroot pigweed (Amaranthus retroflexus L., Amaranthaceae). In all olfactometry bioassays, treatment odors were compared against three controls (humidified air). Results showed that A. iole females were consistently attracted to odors derived from different plant–L. hesperus complexes, while odors from plants subjected to nonhost (S. exigua) or mechanical damage and L. hesperus females alone were not attractive or only variably attractive. These findings suggest that while searching for hosts A. iole females use specific volatiles induced by L. hesperus feeding and oviposition to locate hosts inhabiting a wide variety of plants, including annual and perennial species from four plant families. It was suggested that future research should seek to identify the chemical elicitors involved in the release of plant volatiles attractive to A. iole females.

Discovery of Paratelenomus saccharalis (Dodd) (Hymenoptera: Platygastridae), an Egg Parasitoid of Megacopta cribraria F. (Hemiptera: Plataspidae) in its Expanded North American Range

Megacopta cribraria F. (Hemiptera: Plataspidae), commonly known as the kudzu bug or bean plataspid, was fi rst discovered in the Western Hemisphere in October 2009 (Eger et al. 2010. Insecta Mundi 121:1 11). The plataspid quickly spread from the 9 northeastern Georgia counties in which it was initially confi rmed into 383 additional counties in Alabama, Florida, Georgia, Mississippi, North Carolina, South Carolina, Tennessee, and Virginia by the end of 2012 (Gardner et al. 2013. J. Entomol. Sci. 48:118 127). Subsequent reports show that the insect has now been confi rmed in 4 additional states – Delaware, Kentucky, Louisiana, and Maryland – and the District of Columbia, bringing the total number of confi rmed states to 12 (W.A. Gardner, unpubl. data). Ruberson et al. (2013, Appl. Entomol. Zool. 48:3 13) reported that several existing generalist predators and a single entomogenous pathogen had been recorded as attacking M. cribraria in its expanded range in the southeastern U.S. They also reported a tachinid, Phasia robertsonii (Townsend), parasitizing a single adult M. cribraria in 2012, but no parasitism of eggs or immatures was observed in their 2010 and 2011 surveys in Georgia. Golec and Hu (2013, J. Entomol. Sci. 48: In Press) discovered Strongygaster triangulifer (Loew) (Diptera: Tachnidae) parasitizing individual adults (mean parasitism = 5.14%; n = 214) collected from soybean, Glycine max (L.) Merr.,

Temperature-Dependent Life History of Eretmocerus eremicus (Hymenoptera: Aphelinidae) on Two Whitefly Hosts (Homoptera: Aleyrodidae)

Abstract The effects of temperature on insect life history were studied for two whitefly hosts (Homoptera: Aleyrodidae), the silverleaf whitefly, Bemisia argentifolii Bellows & Perring, and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), as well as the parasitoid, Eretmocerus eremicus Rose & Zolnerowich (Hymenoptera: Aphelinidae) attacking both hosts. Mean egg numbers as a function of time were fitted to models for age-specific oviposition for each whitefly. For B. argentifolii, numbers of eggs laid increased with time at 15, 21, and 24°C. At 28 and 32°C, the curve declined after 6 d, although the model fit was poor. The model did not fit the oviposition data at 32°C. Maximal oviposition rate occurred at 24°C (12 eggs per 48-h period), and the model was almost linear. For T. vaporariorum, the model closely fit mean eggs laid, with highest rates of ≈12 eggs per 48 h at 21 and 24°C. Numbers of whitefly eggs as a function of time and temperature were described by a three-dimensional surface model that was also used to estimate temperature thresholds for oviposition (12.5°C for B. argentifolii and 10.9°C for T. vaporariorum). Increasing temperatures produced decreased preoviposition periods in B. argentifolii, whereas temperature extremes resulted in longer periods for T. vaporariorum. Development times from egg to adult, percentage mortality, and estimated degree-days for development were measured at 15, 21, 24, 28, and 32°C for both whiteflies, and for E. eremicus reared on both hosts. Development rate was higher for B. argentifolii than T. vaporariorum at 24 and 28°C. Development of E. eremicus was faster using B. argentifolii as hosts than T. vaporariorum at 24, 28, and 32°C. By extrapolation of development rates, lower developmental thresholds (°C) were estimated as follows: T. vaporariorum, 2.92; B. argentifolii, 10.32; E. eremicus on T. vaporariorum, 5.44; and E. eremicus on B. argentifolii, 8.7. Mean degree-day requirements for egg to adult development were calculated for T. vaporariorum, 483.4; B. argentifolii, 319.7; E. eremicus on T. vaporariorum, 417.3; and, E. eremicus on B. argentifolii, 314.4. Percentage mortality also was significantly affected by temperature in both species of whitefly. For T. vaporariorum, higher temperatures caused higher levels of mortality, with almost 98% killed at 32°C. The reverse occurred in B. argentifolii, where highest levels of mortality were found at the lowest temperatures. Mortality patterns in E. eremicus reflected those of the host: increasing with temperature on T. vaporariorum, while decreasing on B. argentifolii. The life history of E. eremicus was profoundly affected by that of its host.