Effectiveness of hand removal for small-scale management of Japanese beetles (Coleoptera: Scarabaeidae).

Hand removal is often recommended as a method for small-scale control of Japanese beetles (Popillia japonica Newman). In this study, we investigated the effectiveness of daily hand removal for controlling damage by Japanese beetles on grape plants. We also investigated whether the timing of the removal (at 0800, 1400, or 1900 hours, or at all 3 periods) influenced the effectiveness of the technique. We found that hand removal significantly lowered the number of beetles on, and consequently the damage to, grape plants relative to nonremoval controls. Of the single removal treatments, removal of beetles at 1900 hours was most effective, with results similar to removing beetles three times per day. The majority of beetles removed from plants during the experiment were female, a pattern that matches our understanding of aggregation formation behavior in the species, and which may serve to enhance the benefits of hand removal. Hand removal seems to work by decreasing the number of feeding beetles, which in turn reduces the release of aggregation kairomones from the plant, and subsequently decreases the attractiveness of the plant to future beetles.

The spatial distribution of the Japanese beetle, Popillia japonica, in soybean fields.

The Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae), is a serious pest of many agricultural and horticultural plants. Relatively little research has investigated the distributions of Japanese beetles in agricultural fields, and this lack of information makes pest management more difficult. In the present study, the spatial distribution of Japanese beetles in soybean fields was examined. Specifically, how the distribution and abundance of beetles was affected by distance from an edge, edge direction, and edge type was examined. An edge effect for density was discovered; beetle numbers decreased significantly with increasing distance from the field edge. The east and south sides averaged higher numbers of beetles than the north and west. Downwind edges, in particular downwind edges adjacent to hedgerows, also had significantly higher beetle densities. In addition, females relatively far from the edge had larger egg loads than those closer to the edge. Differences in aggregation seeking behavior, in combination with movement in relation to wind and obstructions such as hedgerows, are possible explanations for these spatial patterns.

Physiological status of male and female Popillia japonica (Coleoptera: Scarabaeidae) affects mating and grouping behavior.

Because mating may be costly, sexually active males or females are predicted to be in relatively good physiological condition and may preferentially direct their mating behavior toward relatively high-quality mates. We tested this hypothesis in Japanese beetles (Popillia japonica Newman), a pest species in which males and females may be either isolated or in aggregations while feeding on host plants. We examined male size and lipid content and female size and egg load with respect to both their pairing status and whether they were isolated or in aggregations. Males that were paired had the highest lipid levels, and single, isolated males had the lowest. Paired females had the highest egg loads and single, isolated females had the lowest. Neither male nor female size was related to pairing status. Females captured during the times of relatively high pairing frequency (i.e., morning and evening) had higher egg loads than females captured at times of lower pairing frequency (i.e., afternoon). These results suggest that mating and aggregative behaviors in Japanese beetles are dependent on the physiological status of males and the reproductive condition of females.

Behavioral explanations underlying the lack of trap effectiveness for small-scale management of Japanese beetles (Coleoptera: Scarabaeidae).

Traps containing a combination floral and synthetic pheromone lure are used to monitor and manage Japanese beetles, Popillia japonica Newman (Coleoptera: Scarabaeidae). One key factor limiting trap effectiveness for beetle control is the "trap spillover" phenomenon, in which the trap attracts beetles without capturing them, resulting in increased damage to surrounding host plants. We investigated the mechanisms underlying trap spillover by conducting two studies in a soybean field in east central Illinois. In the first study, we set up trap stations for 1 d and compared the sex, size, and egg load (for females) of beetles caught in the traps with those on the plants immediately surrounding the trap, downwind of the trap, at lure-only (no trap) stations, and at control areas. Females caught in traps tended to be smaller than those on plants surrounding the traps, and females attracted to the traps had fewer eggs than those downwind or at control sites. We did not find any difference in male characteristics. In the second study, we observed the behavior of beetles initially approaching traps. Upon initial approach, the majority of individuals landed on plants before making contact with the trap, and those beetles that spent an extended time on the leaves tended to be females. Arriving males would occasionally pair with these females on the plants. Overall, traps did not capture a random subset of the beetles present in the field. We hypothesize that trap spillover is a result of arriving females not being as attracted to the precise location of the trap as they are to the general location itself, and of arriving males seeking mates and finding them among these spillover females.

Physical contests for females in the Japanese beetle, Popillia japonica.

Abstract We conducted field observations of physical competition for mates, in which a single male attempts to usurp a female from another male, in male Japanese beetles, Popillia japonica Newman (Coleoptera; Scarabaeidae). Physical contests for mates were relatively rare, but when they occurred the challenger male was able to successfully takeover females by dislodging the previously paired resident male in only 18% of contests, suggesting that a substantial prior residency advantage exists in this species. Challenger males that were successful in takeover attempts were significantly larger than the resident male. In contrast, no size pattern was found between intruding males and residents in unsuccessful takeover attempts. The frequency of contests for existing pairs was examined throughout the day. Pair frequency was greatest in early morning and in the evening but contest frequency was highest during the middle of the day. Contest frequency was negatively related to beetle density but not related to temperature. Overall, physical contests for mates appear to be an important part of the mating behavior in Japanese beetles. The frequency of the contests relates to the time of day and social conditions and contest outcome is related to prior residency and the size of the intruding male relative to the paired male.

The social environment affects mate guarding behavior in Japanese beetles, Popillia japonica.

The effect of the social environment on post-copulatory mate guarding duration in Japanese beetles, (Popillia japonica Newman), was examined in a laboratory experiment. The mate guarding durations of beetles in different sex ratios and densities were observed for 10 hours. Guarding duration was longer when females were larger, suggesting the presence of 'cryptic' male mate choice. Densities, but not sex ratio, affected the duration of guarding bouts, with males guarding for longer at higher densities. This result implies that males increase their guarding duration under conditions in which their female may be likely to be encountered by other males. The lack of a sex ratio effect on the duration of guarding bouts is consistent with other studies on this species that indicate males have difficulty distinguishing females from males. Consequently, because the sex ratio on food plants is typically male-biased, a paired male may react just to density, treating surrounding individuals as if they were mostly males. The total amount of time males spent guarding was lower at lower densities and at male-biased sex ratios; this suggests that after ceasing to guard one female, males were less able to find a subsequent mate under these conditions.

Delayed olfactory nerve regeneration in ApoE-deficient mice.

Apolipoprotein E (apoE), a lipid transporting protein, is extensively expressed in the primary olfactory pathway, but its function is unknown. We previously reported increased apoE levels in the olfactory bulb (OB) following olfactory epithelium (OE) lesion in mice, and hypothesized that apoE may play a vital role in olfactory nerve (ON) regeneration. To directly test this hypothesis, we examined the rate of ON regeneration following OE lesion in apoE deficient/knockout (KO) and wild-type (WT) mice. OE was lesioned in 2- to 3-month-old mice by intranasal irrigation with Triton X-100 (TX). OB were collected at 0, 3, 7, 21, 42, and 56 days post-lesion. OB recovery was measured by both immunoblotting and immunohistochemical analysis of growth cone associated protein (GAP) 43 and olfactory marker protein (OMP). The results revealed that (1) OMP recovery in the OB was significantly slower in apoE KO compared to WT mice; (2) recovery of glomerular area was similarly slower; and (3) GAP43 increases and return to prelesion levels in the OB were slower in KO mice. Together, these results show that olfactory nerve regeneration is significantly slower in KO mice as compared to WT mice, suggesting apoE facilitates olfactory nerve regeneration.

Olfactory function in apoE knockout mice.

Apolipoprotein E (apoE), a lipid transporting protein, has been shown to play a vital role in nerve repair and remodeling. Since the olfactory system is in a continuous state of remodeling, the present study tested the hypothesis that apoE is required for normal functioning of the olfactory system. Olfactory behavior of wild-type (WT) and apoE-deficient (apoE KO) mice was assessed by using three standard olfactory tests: (1) the buried food pellet (BFP) test; (2) the odor choice (OC) test; and (3) the odor cued taste avoidance (OCTA) test. ApoE KO mice performed poorly in all the three tests as compared to WT mice, although they learned the tasks at a rate comparable to WT mice. ApoE KO mice had a significantly longer latency to find the buried pellet than WT mice. In the OC experiment, apoE KO mice did not differentiate water from an odorant solution. Furthermore, in the OCTA test the apoE KO mice were significantly less successful than WT mice at avoiding water containing an odorant and a bad tastant. These data demonstrate that apoE deficiency in apoE KO mice leads to a deficit in olfactory function, suggesting an important role for apoE in the olfactory system.