Interaction between the subterranean termite Reticulitermes flavipes (Isoptera: Rhinotermitidae) and the entomopathogenic fungus Metarhizium anisopliae in foraging arenas

The entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorokin was tested in the laboratory against field-collected groups of eastern subterranean termite, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae), in foraging arenas to determine the potential effect of a "trap and treat" protocol (trapping a part of the population, treating it with a biological control agent and releasing it back into the original population). Individual termites were treated with a suspension of M. anisopliae conidia and released back into the arenas containing untreated termites. After 5 d, 90% of the treated termites died in the arena, but untreated termites did not exhibit a significant increase in mortality within 90 d after release, indicating no transfer of viable M. anisopliae and no epizootic. Although M. anisopliae was isolated from the arenas after 90 d, the average number of fungal colony-forming units recovered was <0.1% of the conidia introduced.     

Parthenogenetic reproduction in neotenics of the subterranean termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Experiments with artificial colonies consisting of only female workers and those of female nymphs and workers of a subterranean termite, Reticulitermes speratus, showed that neotenics (ergatoids and nymphoids) can reproduce parthenogenetically. The larvae hatched from the eggs produced partheno‐genetically by the neotenics were all female and did not have any aberrant external morphology. They had 42 chromosomes and were diploid. The analysis of genotypes at microsatellite loci revealed that the eggs produced parthenogenetically had only one of the two alleles that the mother neotenics possessed, indicating that the eggs were produced by automixis.     

Factors affecting mate choice in the subterranean termite Reticulitermes chinensis (Isoptera: Rhinotermitidae)

Termites are a group of eusocial insects. Mate choice is the most important step which affects the subsequent new colony foundation and development in termites. This study investigated the effects of the four factors on mate choice in the subterranean termite Reticulitermes chinensis Snyder, including colony origin, entry time, physical damage of antennae, and fresh body weights of male dealates. The results showed that the pairing number of dealates from the different colonies was significantly higher than that from the same colonies. The male dealates with early entry time achieved a significantly higher pairing number than the male dealates with late entry time. The male dealates with complete antennae achieved a the significantly higher pairing number than the male dealates lacking the six terminal segments of antennae. Moreover, the heavier male dealates achieved a significantly higher pairing number than the lighter male dealates. However, there were no significant differences in the pairing time for all the experimental treatments. These results suggested that the male dealates, which are heterogenous, healthy, heavy, and more familiar with the environment in R. chinensis, have the obvious advantages in the mate choice. This rule of mate choice is helpful for termites to avoid inbreeding and to maintain the genetic diversity of offspring, which is very important for the environmental adaptability and development of termite colonies.     

Patterns of neotenic differentiation in a subterranean termite, Reticulitermes speratus (Isoptera: Rhinotermitidae)

Plasticity in the caste developmental pathway is a remarkable characteristic of termite societies. In Reticulitermes, two types of neotenic reproductive, nymphoids and ergatoids, may differentiate from nymphs and workers and take over reproduction in the colony after the death of the original primary reproductive pair. We examined the dynamics of newly differentiated nymphoids and ergatoids in experimentally orphaned laboratory colonies of R. speratus with different caste compositions. The period required for differentiation of nymphoids was shorter than that for differentiation of ergatoids. The sex ratio of neotenics was strongly female‐biased, particularly in ergatoids. The results suggested that the number of differentiated ergatoids was restricted by the existence of nymphs or nymphoids in a colony. Workers were assumed to kill most newly differentiated neotenics. Attack reflecting conflict between colony members is probably an important mechanism to control neotenic emergence.     

Resistance of insecticide-treated foam board insulation against the eastern subterranean termite and the Formosan subterranean termite (Isoptera: Rhinotermitidae)

Three foam board types, one untreated control, one containing 2,000 ppm disodium octaborate tetrahydrate (DOT), and one containing 1,000 ppm deltamethrin, were exposed to field populations of the eastern subterranean termite, Reticulitermes flavipes (Kollar), and the Formosan subterranean termite, Coptotermes formosanus Shiraki. There was no significant difference in termite damage between foam boards treated with 2,000 ppm DOT and the untreated control. Form boards containing 1,000 ppm deltamethrin were not damaged by R. flavipes, whereas only minor damage occurred after exposure to C. formosanus.     

Toxicity and in vitro metabolism of t-permethrin in eastern subterranean termite (Isoptera: Rhinotermitidae)

Toxicity and metabolism of t-permethrin were evaluated in two colonies (UF and ARS) of the eastern subterranean termite, Reticulitermes flavipes (Kollar), collected in Gainesville, FL. The UF colony (LC50 = 1.86 micrograms per vial) was approximately twofold more tolerant of t-permethrin than the ARS colony (LC50 = 0.89 microgram per vial) at the LC50. The synergists piperonyl butoxide and S,S,S-tributylphosphorotrithioate increased t-permethrin toxicity four- and threefold (at the LC50) in the UF and ARS colonies, respectively. Despite these differences in t-permethrin susceptibility, microsomal oxidase activities toward surrogate substrate (aldrin epoxidase, and methoxyresorufin O-demethylase), cytochrome P450 content, and microsomal esterase activity toward alpha-naphthyl acetate did not differ significantly between the colonies. Moreover, no significant differences in qualitative and quantitative metabolism of [14C]t-permethrin were observed between the UF and ARS colonies for three enzyme sources (microsomal oxidase, microsomal esterase, and cytosolic esterase). Based on in vitro metabolism assays, the major detoxification route of t-permethrin in the UF and ARS termite colonies appears to be hydrolysis catalyzed by microsomal esterases.     

Distribution of Formosan subterranean termite (Isoptera: Rhinotermitidae) in Mississippi

An extensive monitoring and survey program in Mississippi was conducted from 2000 to 2004 to investigate the distribution of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae). Seventy-two towns from 22 counties in southern Mississippi were monitored with a total of 3914 traps that catch alates during the swarming season. In addition, 259 licensed pest management professionals in Mississippi were surveyed to determine the locations of termite infestations treated. The alates of C. formosanus were recovered in 12 counties with light traps, and termite infestations were documented in an additional 13 from data collected in the termite survey. Infestations of C. formosanus have been documented in urban, urban cluster, rural, and forested areas of Mississippi. However, the distribution in mean total capture of alates for 4 yr differed significantly among the four ecological areas with the highest percentage in forested areas (31%) and the lowest percentage in urban cluster areas (17%). Most of the infestations of C. formosanus were geographically distributed along the coastal areas of southern Mississippi from Gulfport to Pascagoula. The greatest total number of alates captured in light traps was documented in Pearl River County. Mass swarming of C. formosanus occurred primarily in May or June, depending on weather conditions. The number of documented counties with the evidence of large and widely dispersed swarms of C. formosanus in different ecological areas, and the increase in total annual alate captures from 2000 to 2003, suggest that this invasive termite species is now firmly established in Mississippi.     

Flight Speed of Tethered Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) Alates

Alates of the Eastern subterranean termite, Reticulitermes flavipes (Kollar) were collected over two flight seasons (2002 and 2004) and flown on flight mills. Data were collected to test if alate mass, colony origin, or gender influenced flight speed. Flight speed ranged from 3.14 to 69.12 cm s⁻¹ and the maximum distance flown by an alate was 458.3 m. Alate mass (P = 0.9406), gender (P = 0.3976), colony origin (P = 0.1244), and the interaction of gender and colony (P = 0.7093) did not significantly influence flight speed. Additionally, an electronic counting device was used to provide instantaneous flight speeds and allowed flight speed to be modeled during acceleration, cruising, and deceleration periods of flight. Mean (±SEM) flight speeds in 2004 were 20.64 (±2.21) cm s⁻¹ (n = 13) for males and 17.76 cm s⁻¹ (n = 1) for the single female flown, falling within the range of the 2002 values.     

Immunomarking reveals food flow and feeding relationships in the eastern subterranean termite, Reticulitermes flavipes (Kollar)

Trophallaxis and feeding relationships in the eastern subterranean termite, Reticulitermes flavipes (Kollar), were examined using a novel marking technique, rabbit IgG protein coupled with an enzyme linked immunosorbent assay (ELISA) to detect the marker. Transfer experiments in small dishes evaluated the trophallactic transfer of the marker from donor workers fed IgG-treated paper to recipient workers or larvae. Worker donors rapidly acquired the marker, and 100% of donors tested positive within 24 h. Trophallactic transfer from donors to recipients was relatively inefficient, and 51 +/- 2% of recipient workers and 31 +/- 2% of recipient larvae tested positive at 72 h. Based on the mean optical density counts, approximately 27% of marker ingested by the donors was passed on to the recipient workers in the first 24 h, 14% to recipient larvae, and 26% to recipient soldiers. The ability of soldiers to feed independently of workers was examined in dish assays. Soldiers showed no significant uptake of the marker when isolated from the workers, and uptake increased significantly when workers were present. The distribution of the marker was further studied in larger colony fragments composed of workers, soldiers, nymphs, and larvae. Marker acquisition by the different castes/developmental stages was highly variable, with workers and nymphs acquiring the marker at a faster rate than soldiers and larvae. The results of this study contribute to our understanding of the foraging ecology and social behavior in R. flavipes. In addition, they may help design improved control programs for subterranean termites based on baits.     

Effects of sublethal exposure to imidacloprid on subsequent behavior of subterranean termite Reticulitermes virginicus (Isoptera: Rhinotermitidae)

Experiments were conducted to determine whether subterranean termites, Reticuliternes virginicus (Banks), previously exposed to sublethal doses of imidacloprid (Premise), and allowed to recover for 1 wk, demonstrated behavioral aversion to a subsequent exposure. Worker termites experiencing a previous sublethal but debilitating exposure to imidacloprid-treated sand (either 10 or 100 ppm for 4 h) showed no apparent aversion to a second encounter with imidacloprid-treated sand under conditions of this experiment. If these laboratory results hold in the field and termites traveling through a zone of soil treated with imidacloprid are impaired but subsequently recover, they will be just as likely as their naive nestmates to reenter the treated area if their travels take them through the nonrepellent application a second time. Our results also indicate that a sublethal exposure to imidacloprid can affect termite tunneling behavior. Many worker termites that received an initial 4-h exposure to 100 ppm imidacloprid-treated sand died, but those that survived tunneled significantly less than did their naive nestmates, as did some termites exposed to 10 ppm imidacloprid.     

A mathematical model for the territorial competition of the subterranean termites Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae)

The foraging territories of two subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), were simulated using a two-dimensional model to explore how territorial competition changes according to two variables characterizing territory formation: the total number of territories, and the blocking probability. Meanwhile, the blocking probability quantitatively describes the likelihood that a tunnel will be terminated when another tunnel is encountered. In our previous study, we introduced an interference coefficient γ to characterize territorial competition, and obtained γ as a function of the total number of territories and the blocking probability for a single termite species by model simulation. In the field, the territorial competition of more than two termite species is frequently observed. Here, we extended the γ function to be able to explain the competition between the two species by applying statistical regression to the simulation data. Further, we statistically checked the extended γ function by comparing the γ function for a single species. We also discuss another approach to mathematically derive the extended γ function, which can be easily generalized for use in cases of territorial competition involving more than two termite species.     

Influence of soil compaction on tunnel network construction by the eastern subterranean termite (Isoptera: Rhinotermitidae)

Eastern subterranean termites, Reticulitermes flavipes (Kollar), workers were introduced into arenas containing low, moderate, and high compaction builder's sand (1.05 g/cm3, 1.18 g/cm3 or 1.35 g/cm3 bulk densities, respectively), and they immediately began tunneling. Termites built the tunnel network significantly fastest in soil of low compaction compared with moderately or highly compacted soil. In soil of low compaction, 221.67 +/- 4.73 cm of total tunnel distance was constructed in 1 d compared with only 96 cm of tunneling in highly compacted soil. At 14 d, total tunnel distance averaged 216.83 +/- 4.56 cm in soil of low compaction compared with 169.70 +/- 4.10 and 181.18 +/- 6.13 cm in moderately and highly compacted soil, respectively. Decreases in total tunnel distance between 1 and 14 d were caused by backfilling of seldom-used tunnels. Termites did the majority of tunneling during the first day of introduction into arenas. In soil of low and moderate compaction, termites essentially constructed the entire tunnel network within the first day, only modifying it by backfilling or maintaining tunnels. In highly compacted soil, 53% of the final tunnel network was constructed during the first day, 87% was constructed by the third day, and 97% was constructed by the seventh day. Soil compaction did not affect the number of primary tunnels or the number and diameter of secondary tunnels. The angle between the secondary tunnel and primary tunnel also was not significantly affected by soil compaction. However, the number of secondary tunnels in soil of low compaction (5.89 +/- 0.51) was significantly greater than in moderately (2.74 +/- 0.36) and highly (3.58 +/- 0.59) compacted soils.     

Effect of nutritional condition on larval food requisition behavior in a subterranean termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Although optimal investment theory would be similarly applicable to eusocial insects to maximize colony reproductive outputs, directly distinguishing an amount of investment in each larva should be a difficult task for workers because of the characteristics of group living. Thus, it is expected that workers adjust brood care by using a cue or signal conveying information of larval status. In termites, which are typical group of eusocial insects, there are nevertheless few direct observations on worker brood care and little is known about cues inducing worker feeding. I show here that a Japanese subterranean termite Reticulitermes speratus uses an overt food solicitation by larva, “pecking”, as a cue for worker feeding. Direct observations demonstrated that workers feed larvae in response to larval pecking. Furthermore, nutritional experiments showed that larvae exhibited pecking more frequently when their nutrient status is lower; hence, pecking may be an honest reflection of larval hunger status. These results indicate that workers can feed more starved larvae than less starved ones because pecking honestly reflects larval hunger state. That is, feeding in response to pecking should standardize the total amount of food intake of each larva and help a termite colony make worker investment efficient.     

Effects of soil cations on the foraging behavior of Reticulitermes flavipes (Isoptera: Rhinotermitidae)

This study examined soil cation concentration gradients around decomposing logs and determined whether Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) builds galleries in soil substrates containing those cations versus soils without, presumably in an effort to forage efficiently. Soil samples were collected at different depths and lateral distances from decomposing logs containing termites, freshly fallen logs without termites, and bare soil locations at 10 sites to determine whether cation gradients existed in a forest floor. Analyses of cation gradients were significant for potassium, calcium, and magnesium; however, only potassium showed a significant gradient where concentrations decreased with depth and lateral distance from a decomposing log. R. flavipes was then tested in laboratory bioassays to determine if they were attracted to salt cation solutions. Linear foraging distance was significantly greater in artificial K2CO3 gradients than in controls. The results from this study suggest that potassium is found in gradients around decomposing logs and that R. flavipes is attracted to this cation.     

Field evaluation of potential control strategies against the invasive eastern subterranean termite (Isoptera: Rhinotermitidae) in Chile

Four different termite control strategies consisting of two soil treatments with cypermethrin and fipronil and two bait treatments with hexaflumuron and sulfluramid were evaluated for their efficacy and potential for controlling the invasive eastern subterranean termite, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae), in Quillota and Valparaiso, Chile. Monitoring stations were installed at all sites to measure the overall termite activity next to and at distances up to 30 m away from infested structures, most being 3-5 m. Foraging activity was extremely seasonal with the maximum consumption rates occurring from January to April. Termite foraging activity was low from July to September. After treatments in January 2003, there was a significant decrease in wood consumption, percentage of active stations, and numbers of termites in traps for the first 6 mo with hexaflumuron baits. No significant change in R. flavipes foraging activity was observed on wood consumption and percentage of active stations for sulfluramid bait or cypermethrin and fipronil soils treatments. The seasonal pattern of foraging activity remained unchanged for all treatments in 2004 and 2005, except structures baited with hexaflumuron. Feeding activity at the monitors in the area surrounding the hexaflumuron baits declined to 0 after January 2004. Alate flights occurred in approximately 38% of the structures treated with cypermethrin and sulfluramid bait in 2003 and in approximately 40% of the structures treated with cypermethrin, fipronil, and sulfluramid bait in 2004. Sulfluramid baits and cypermethrin soil treatments did not have any impact within a 15-m radius of the structures. Soils treatments of fipronil and cypermethrin prevented termites access in 75% of the homes. The number of active monitoring stations only declined within 2 m of the fipronil-treated zone. Hexaflumuron exhibited a reduction in activity for at least a 15-m radius.